Influence of Short Carbon and Glass Fibers on the Mechanical Performance, Thermal Stability, and Fracture Behavior of FDM-Printed Composites

Influence of Short Carbon and Glass Fibers on the Mechanical Performance, Thermal Stability, and Fracture Behavior of FDM-Printed Composites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Influence of Short Carbon and Glass Fibers on the Mechanical Performance, Thermal Stability, and Fracture Behavior of FDM-Printed Composites Frederico de Castro Magalhães, Andrea Del Pilar Fabra Rivera, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7336068/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 16 Oct, 2025 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted 5 You are reading this latest preprint version Abstract Fused Deposition Modeling (FDM) is a widely used additive manufacturing technique due to its efficiency in producing complex structures at low cost with minimal material waste. However, weak interlayer adhesion and void formation limit the mechanical performance of printed components. This study evaluates the effect of short fiber reinforcement (carbon and glass) and printing orientation (0°/90° and 45°/-45°) on the mechanical properties, fracture resistance, and thermal stability of FDM-printed composites. PLA, PLA-CF, and PLA-GF, each reinforced with 20 wt% short carbon or glass fibers, were analyzed. Tensile, flexural, and fracture toughness (K IC , G IC , P Q ) tests were performed according to ASTM standards, along with thermogravimetric analysis (TGA), porosity measurements, and fracture surface characterization using scanning electron microscopy (SEM). PLA exhibited the highest tensile strength in a 45°/-45° orientation (50.83 MPa), while PLA-GF in 0°/90° showed the highest flexural strength (17.79 MPa). Fracture resistance followed a similar trend, with PLA-GF achieving the highest K IC (4.71 MPa·m¹/²) and P Q (1186.66 N), while PLA exhibited the highest G IC (10.31 kJ/m²). Fractographic analysis revealed fiber pull-out and interfacial debonding, indicating differences in fiber-matrix adhesion. TGA confirmed a higher thermal stability for PLA-CF, while porosity analysis demonstrated a direct correlation between void content and mechanical performance. These findings emphasize the role of fiber type, printing orientation, and microstructural integrity in the mechanical behavior of FDM-printed composites, particularly for applications requiring enhanced fracture resistance. Additive manufacturing FDM short fibers PLA fiber-reinforced polymer composites Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. INTRODUCTION Fused Deposition Modeling (FDM) is one of the most widely used techniques in additive manufacturing for reconstructing parts, enabling the three-dimensional production of components from designs created in Computer-Aided Design (CAD) software. This process has been extensively studied due to its versatility and applicability in various fields [ 1 , 2 , 3 ]. During the FDM process, material is deposited layer by layer onto the printer bed, following pre-defined instructions set in a G-code file, ensuring precise geometric reproduction [ 4 , 5 , 6 , 7 ]. The FDM technique offers several advantages, including the ability to produce complex designs, cost-effectiveness, short lead times, and repeatability. As noted by John et al. [ 8 ] and Cózar et al. [ 9 ], these benefits have led to its adoption in the medical, aerospace, automotive, and engineering industries. Conventional manufactured parts can be replaced by lighter and more flexible components, thereby reducing energy consumption and material waste in the aerospace industry [ 10 , 11 ]. However, despite these advantages, FDM-printed parts exhibit mechanical limitations when compared to conventionally manufactured components, mainly due to their layer-by-layer structure, which introduces anisotropy and interlayer defects [ 12 ]. Otherwise, Ponticelli et al. [ 13 ] proposed the replacement of conventional aluminium-made brackets for overhead locker within commercial aircrafts by manufactured composite PEEK-Carbon fibres (10%) using FDM technology. The authors showed that it was possible to identify a reduction, not only in the production costs, but also on environmental impacts associated with aviation area, improve sustainability of sector. Hernandez et al. [ 12 ] and Agarwal et al. [ 13 ] reported that the mechanical properties of parts manufactured using FDM technology differ from those produced through conventional processes. Studies show that the tensile strength of FDM-printed parts can be between 10% and 73% lower than that of injection-molded counterparts, due to intrinsic voids and weak interlayer adhesion [ 12 , 13 , 3 ]. Mei et al. [ 14 ] and Dong et al. [ 15 ] highlight that the presence of voids and gaps between layers is a primary factor contributing to these decreased mechanical properties. Türk et al. [ 16 ] and Geng et al. [ 17 ] attribute the source of these voids and gaps to factors such as inadequate printing parameters, limitations in stepper motor precision, and material deposition settings, which directly impact part performance. Therefore, adjusting the printing parameters and selecting appropriate reinforcement strategies contribute to enhancing the structural integrity of FDM parts. Furthermore, Ding et al. [ 18 ] and Maqsood et al. [ 19 ] note that the material extruded using the FDM technique cools rapidly from the glass transition temperature to ambient temperature. This rapid cooling generates internal stresses that can reduce interlayer adhesion, leading to crack formation, delamination, and anisotropic mechanical behavior. Studies show that flexural strength can be reduced by up to 40% due to these effects [ 20 ]. Gao et al. [ 20 ] and Adeniran et al. [ 21 ] reinforce that these factors impact both inter- and intralaminar deformation, reducing the mechanical properties considerably. To address these issues, researchers have explored alternative solutions such as modifying processing parameters, improving adhesion techniques, and incorporating fiber reinforcements to counteract weaknesses inherent to FDM-printed structures [ 22 , 23 ]. According to Bian et al. [ 22 ] and Shah et al. [ 23 ], several studies are currently underway to analyze and comprehend the mechanical behavior of parts manufactured using the FDM technology. Wickramasinghe et al. [ 24 ] and Prajapati et al. [ 25 ] indicate that mechanical performance can be improved by adjusting printing parameters, annealing, snap-fitting, printing in an oxygen-free environment, mechanical pressing, and the use of fiber-reinforced polymer composites. These methods have demonstrated effectiveness in reducing void content and enhancing interlayer adhesion, contributing to increased mechanical strength and dimensional stability. For example, annealing has been shown to increase tensile strength by up to 20% and improve interlayer bonding, while adjusting raster orientation and infill density can lead to an increase of up to 30% in Young’s modulus [ 24 , 25 ]. However, while significant advancements have been made in adjusting FDM parameters, the role of fiber reinforcement in overcoming anisotropic effects and void formation requires further investigation. Among the available polymer matrices for additive manufacturing, polylactic acid (PLA) stands out due to its ease of processing, biodegradability, and good mechanical performance relative to other thermoplastics used in FDM [ 22 ]. However, PLA exhibits inherent brittleness and low impact resistance, limiting its applicability in structural components [ 20 ]. To enhance the mechanical properties of PLA while maintaining its printability, reinforcement with short fibers has been explored as a viable approach. Short carbon and short glass fibers were selected as reinforcements in this study due to their ability to significantly improve stiffness, strength, and thermal stability without the challenges associated with continuous or long fibers, such as poor dispersion and excessive viscosity during extrusion [ 24 , 25 ]. Hofstatter et al. [ 26 ] and Akhoundi et al. [ 27 ] note that fiber-reinforced polymer composites are well-known for their high stiffness, mechanical strength, fatigue resistance, and corrosion resistance. Ismail et al. [ 28 ] reported that short carbon fiber reinforced polymer composites fabricated via FDM can achieve tensile strengths of up to 67 MPa and Young’s moduli around 8.4 GPa, depending on fiber weight percentage and processing conditions [ 27 ]. Parmiggiani et al. [ 29 ] emphasize that fiber orientation plays a critical role in mechanical performance, with continuous fiber composites achieving tensile strengths as high as 800 MPa when fibers are aligned in the load direction, whereas short fiber-reinforced composites typically range between 150 MPa and 400 MPa. Previous studies have shown that fiber content above 40 wt% can lead to percolation effects, causing significant flow issues, nozzle clogging, and poor layer adhesion [ 20 , 21 ]. Thus, a reinforcement level of 20 wt% was chosen to ensure processability while maintaining improvements in mechanical properties. Li et al. [ 31 ] reported that this reinforcement percentage leads to a significant increase in tensile modulus while preserving print quality. However, the relationship between moderate fiber content (20 wt%) and print orientation remains underexplored, despite its relevance in achieving a compromise between printability and mechanical performance in FDM composites. Zhang et al. [ 32 ] report that incorporating fibers into a polymer matrix reduces stress concentration and increases stiffness. This behavior is typical of fiber-reinforced composites, where the fibers’ lower ductility compared to the polymer matrix limits deformation before fracture. Short carbon fibers (PLA-CF) typically have lengths between 100–400 µm and diameters ranging from 7–13 µm, with optimal reinforcement effects observed for fibers around 150 µm [ 33 ]. Short glass fibers (PLA-GF) in 3D-printed composites often range from 200–400 µm in length, with a diameter of approximately 10 µm, improving impact resistance by up to 54% compared to pure polymer matrices [ 34 ]. Although fiber-reinforced FDM composites have been extensively studied, most research has focused on individual parameters such as raster angle or fiber content, without considering their combined effects. Moreover, previous studies have primarily investigated continuous fiber composites or higher fiber loadings (> 30 wt%), which can introduce processability challenges such as increased viscosity, extrusion difficulties, and nozzle clogging, ultimately compromising layer adhesion and print quality [ 35 , 36 , 37 ]. Therefore, further research is needed to systematically evaluate moderate fiber reinforcement levels under different printing orientations to better understand their impact on mechanical performance. To address the existing knowledge gaps in the additive manufacturing of fiber-reinforced composites, this study evaluates the mechanical behavior of FDM-printed thermoplastic composites reinforced with short glass and carbon fibers. Commercially available PLA-CF and PLA-GF filaments with nominal fiber dimensions (160 µm length, 13 µm diameter) and a stated reinforcement percentage of 20 wt%, as provided by the manufacturer, ensuring consistency in material properties while maintaining good extrudability. The effect of print orientation (0°/90° and 45°/-45°) is analyzed, as raster angle variations significantly influence mechanical performance, particularly in fiber-reinforced composites [ 38 ]. Comparative analyses between PLA, PLA-CF, and PLA-GF are conducted to quantify the impact of fiber type and orientation on tensile strength, four-point bending strength, and fracture toughness, providing insights into how fiber alignment and interlayer adhesion affect mechanical response. By examining these variables, this study aims to provide a broader understanding of the mechanical behavior of fiber-reinforced FDM composites, supporting improved material selection and printing strategies for high-performance applications. 2. MATERIALS AND METHODS To achieve the proposed objectives, a structured research plan was established, as illustrated in Fig. 1 , which presents the flowchart outlining the steps of this study. Initially, the PLA, PLA-CF, and PLA-GF filaments were analyzed through thermogravimetric analysis (TGA) to validate their fiber content and thermal stability. Optical microscopy was then used to assess fiber dispersion within the polymer matrix. After these characterizations, specimens were fabricated following the specifications of ASTM D3039 for tensile testing, ASTM D7264 for four-point bending tests, and ASTM D5045-99 for the evaluation of fracture parameters, including the critical load (P Q ), fracture toughness (K IC ) and strain energy release rate (G IC ). To further investigate the structural integrity of the printed specimens, porosity analysis was conducted, followed by fracture surface characterization using scanning electron microscopy (SEM) to evaluate fiber-matrix interaction and failure mechanisms. The mechanical behavior of fiber-reinforced FDM composites is examined and discussed in the Results and Discussion section. 2.1 Materials The filaments used in this study: PLA, PLA-CF, and PLA-GF are commercially available materials specifically designed for FDM. These filaments were purchased directly from Voolt 3D (Santo André, Brazil), which provided their nominal composition and fiber specifications. According to the manufacturer, the composite filaments consist of a PLA matrix (80 wt%) reinforced with short carbon or glass fibers (20 wt%), with average fiber lengths of 160 µm and diameters of 13 µm. Fiber contents above 40 wt% can cause percolation effects, leading to extrusion difficulties, nozzle clogging, and weak interlayer adhesion. To maintain processability and enhance mechanical performance, the reinforcement fraction was limited to 20 wt%. Additionally, fiber lengths were controlled near 160 µm, as values around 150 µm optimize reinforcement efficiency and printability. Excessive fiber loading (above 30–40 wt%) also increases porosity, reducing stress transfer between fiber and matrix, which weakens tensile and flexural properties. Studies indicate that moderate reinforcement levels (15–25 wt%) improve mechanical strength without compromising print quality, mitigating the drawbacks of high fiber content [ 39 , 40 ]. 2.2 Process Parameters To determine the appropriate extrusion conditions for each filament, a temperature tower test was performed. This test involved printing a stepped structure at varying temperatures to assess extrusion quality, layer adhesion, and defect formation. Based on these observations, the extrusion temperature was set at 210°C, ensuring proper filament deposition while reducing defects such as warping, under-extrusion, and delamination. The printing nozzle diameter was set to 0.4 mm, considering resolution, dimensional accuracy, and filament flow stability. While a 0.8 mm nozzle could help reduce clogging, it often compromises print resolution and layer precision, affecting mechanical property evaluations. The 0.4 mm nozzle ensures consistent filament extrusion and uniform fiber dispersion, which are important for reliable specimen fabrication. The printing speed was set at 15 mm/s, since lower speeds promote stronger layer bonding by allowing more time for the material to spread and fuse properly. Printing speeds above 20 mm/s have been reported to increase void formation and delamination, particularly in fiber-reinforced composites, where heat dissipation occurs more rapidly due to the fiber content. The layer thickness was fixed at 0.2 mm, a widely used parameter in FDM-printed composites. This setting provides a balance between resolution and mechanical integrity—thicker layers tend to weaken interlayer adhesion, while thinner layers extend printing time without offering substantial mechanical improvements. Regarding printing orientation, two raster configurations were selected: 0°/90° and 45°/-45°, as they are commonly used in composite research to assess anisotropic mechanical behavior. The 0°/90° orientation aligns fibers with the principal loading direction, leading to higher tensile strength, while the 45°/-45° orientation introduces shear stresses, improving damage tolerance and energy dissipation. Studies have shown that the combination of axial and shear stress components in 45°/-45° raster patterns enhances impact and fatigue resistance [ 41 , 42 ]. Similarly, Spoerk et al. [ 43 ] demonstrated that different raster angles influence interlayer bonding, which directly affects the overall mechanical response of FDM-printed parts. Although a 0° raster orientation generally provides the highest tensile strength, it is often associated with brittle failure and reduced ductility. On the other hand, 45°/-45° orientations promote greater energy absorption and delay catastrophic failure, leading to more durable structures. Previous research highlights that raster angle selection plays a crucial role in flexural and fatigue behavior, reinforcing the necessity of evaluating both 0°/90° and 45°/-45° orientations to obtain a complete understanding of mechanical performance [ 41 , 42 ]. The specimens were printed using FDM technology, positioned centrally on the printer platform, and fabricated individually to ensure consistency. Table 1 presents the detailed printing parameters applied in this study. All specimens were printed on the XY plane of the heated bed, ensuring uniformity in material deposition and structural integrity. Table 1 Printing Parameters used for Specimen Fabrication. Parameters Values Units Print speed 15 [mm/s] Infill density 100 % Infill patern cubic - Printing orientation [0°/90º] [45°/-45°] [º] Layer height 0.16 [mm] Line width 0.4 [mm] Bed temperature 50 [ºC] Nozzle temperature 210 [ºC] Number of perimeters 4 Wall For slicing the 3D models generated in CAD software (SolidWorks 2008) into individual layers, CURA 5.2 software (Creality Sunlu, China) was used. A dedicated filament dryer (Creality, Sunlu, China) was used to protect the filament spool from moisture absorption, maintaining a temperature of 50°C during the printing process. 2.3 Specimens For the tensile test, the specimens were designed according to the dimensions specified by the ASTM D3039 standard, which included a thickness of 4.5 mm, a width of 13 mm, and a length of 165 mm (Fig. 2 a). The test was conducted at a speed of 3 mm/min, following the standard procedure to accurately assess the tensile properties of the materials. For the four-point bending test, the specimens were designed in accordance with the ASTM D7264 standard. These specifications included a thickness of 10 mm, a height of 20 mm, and a length of 90 mm (Fig. 2 b). The test was conducted at a speed of 2 mm/min to evaluate the flexural strength and modulus of the samples. According to the standard, the test was performed until either the specimen fractured or the displacement of the loading punch reached 13 mm, ensuring compliance with the defined failure criteria. For the fracture analysis, specimens with a single-edge notch were fabricated following the ASTM D5045-99 standard. The test was conducted in a three-point bending configuration with a constant displacement rate to determine the critical load (P Q ), the critical strain energy release rate (G IC ), and the fracture toughness (K IC ). This evaluation provides insights into the crack initiation and propagation resistance of fiber-reinforced composites. 2.4 Testing Equipaments To verify the actual fiber content in the PLA-CF and PLA-GF filaments, thermogravimetric analysis (TGA) was conducted using a TA Instruments Q50 TGA. Samples weighing approximately 10 mg were heated from room temperature to 600°C at a heating rate of 10°C/min under a nitrogen atmosphere to evaluate the thermal degradation profile and residual mass of the PLA, PLA-CF and PLA-GF filaments. The void content of the printed specimens was determined using a gravimetric method based on ASTM D2734. The theoretical density of the material was calculated from its composition, and the actual density was measured using an Analytical Balance Sartorius Entris 224-1S, following standard mass-to-volume ratio procedures. The void content percentage was then computed using Eq. 1 : $$\:V=\left(1-\frac{{\rho\:}_{measured}}{{\rho\:}_{theoretical}}\right).100$$ 1 where 𝜌 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 is the experimentally obtained density and 𝜌 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 is the theoretical density based on the material's composition. Tensile, four-point bending and fracture toughness tests were conducted using a Shimadzu AG-IS universal testing machine with a 100 kN load capacity. Wedge grips moved at a speed of 3 mm/min for the tensile test and 2 mm/min for the four-point bending test, with data collection (force, grip displacement) at 100 Hz, operating at a temperature of 24°C. To investigate the fracture mechanisms and fiber-matrix interaction in the specimens subjected to the tensile test, optical microscopy and scanning electron microscopy (SEM) were performed. Optical micrographs were obtained using a Leica DM750M optical microscope with a high-resolution digital camera. SEM images were acquired to analyze the fracture surfaces after tensile testing, providing insights into fiber pull-out, interfacial adhesion, and failure modes under tensile loading conditions. The critical load (P Q ), the critical strain energy release rate (G IC ), and the fracture toughness (K IC ) are key parameters in evaluating the fracture resistance of structures and components under notched conditions, where high stresses concentrate around the notch regions. In this study, these parameters were determined according to the ASTM D5045-99 standard, which is widely applied to polymer-based materials. This standard provides the methodology for calculating these fracture properties, ensuring consistency in material evaluation. 3. RESULTS AND DISCUSSION To verify the actual fiber content in the PLA-CF and PLA-GF filaments, thermogravimetric analysis (TGA) was conducted. The results confirmed that the fiber reinforcement closely matched the nominal 20 wt% specified by the manufacturer, validating the consistency of the composite formulation (Fig. 3 a) and the Figs. 3 b and 3 c presents optical micrographs of the reinforced filaments, providing qualitative evidence of fiber dispersion within the polymer matrix. The thermal degradation behavior of the PLA, PLA-CF, and PLA-GF filaments was analyzed using TGA, as shown in Fig. 3 a. The onset of weight loss for PLA was observed at approximately 327°C, with the maximum degradation rate occurring around 360°C. The residual mass at 600°C was about 2.5%, indicating minimal inorganic content in the material. For PLA-CF, the onset of thermal degradation was detected at around 334°C, with the peak degradation temperature occurring at 371°C. The final residue at 600°C was approximately 23%, suggesting the presence of carbon fiber content, which does not fully decompose under the tested conditions. Similarly, the PLA-GF filament exhibited an onset degradation temperature of approximately 323°C, with the maximum degradation rate occurring at 359°C. The residual ash content was significantly higher than that of PLA and PLA-CF, reaching about 21.4% at 600°C. This elevated residue aligns with the expected presence of glass fibers, which remain stable at high temperatures and do not decompose under the conditions of the TGA test. The thermogravimetric results confirm the presence of reinforcing fibers in the composite filaments and highlight differences in thermal stability. While carbon fibers provided a slight increase in thermal resistance compared to PLA, the glass fiber-reinforced composite exhibited a significantly higher residual mass due to the non-decomposable nature of the glass content. These findings align with previous studies on fiber-reinforced thermoplastics, demonstrating that fiber type plays a crucial role in the thermal performance of the printed composites. Figure 3 b and 3 c presents optical micrographs of the PLA-CF and PLA-GF filaments, showing the dispersion of carbon and glass fibers within the PLA matrix. As indicated by the arrows, the fibers appear well-embedded in the matrix, with their distribution following the extrusion direction. The morphology observed suggests an adequate dispersion of the fibers, which is essential for ensuring consistent mechanical behavior in 3D-printed composites. However, variations in fiber alignment and possible regions of local agglomeration may influence mechanical performance. However, a detailed analysis of the images reveals variations in fiber alignment and orientation, which may directly impact the mechanical properties. In PLA-GF samples, glass fibers tend to maintain a more uniform alignment along the extrusion direction, leading to a more homogeneous reinforcement distribution within the polymeric matrix. This behavior is favorable for load transfer efficiency in the printing direction, which explains the higher stiffness observed in mechanical tests for the 0°/90° orientation [ 24 , 30 ]. Conversely, in PLA-CF samples, a more dispersed and partially misaligned fiber distribution is observed, with some fibers exhibiting random inclinations or localized agglomerations. This less uniform distribution may reduce the efficiency of load transfer between matrix and reinforcement, leading to stress concentration zones and a decrease in overall reinforcement efficiency. Additionally, the interaction between the polymeric matrix and fibers differs between carbon and glass reinforcements, affecting interfacial adhesion characteristics and contributing to distinct failure mechanisms during mechanical testing [ 32 , 36 ]. The presence of these structural variations aligns with findings from previous studies on FDM-printed fiber-reinforced composites, which highlight that the layer-by-layer deposition and extrusion path significantly influence the final fiber distribution within the polymer matrix. This effect becomes particularly relevant in specimens printed with a -45°/45° orientation, where fiber misalignment may have a more pronounced effect on mechanical strength and deformation response [ 29 , 35 ]. 4.1 Tensile Test Before performing the tensile and flexural tests, the void content of the 3D-printed specimens was measured to assess the influence of fiber reinforcement and printing orientation on porosity levels (Fig. 4 a). The percentage of voids plays a crucial role in determining the mechanical performance of additively manufactured components, as excessive porosity can compromise interlayer adhesion, reduce stiffness, and introduce stress concentration points that accelerate failure. To evaluate the mechanical performance of the reinforced and unreinforced specimens, tensile tests were conducted to determine Young’s modulus (Fig. 4 b), tensile strength (Fig. 4 c), and the maximum force (Fig. 4 d) sustained before failure. These properties are critical for assessing how fiber reinforcement and printing orientation influence material stiffness, strength, and structural integrity. The results obtained are presented in Fig. 4 . Figure 4 a presents the void content for PLA, PLA-CF, and PLA-GF specimens printed in both 0°/90° and 45°/-45° orientations. The results indicate that PLA exhibited the lowest void content, with values of 6.1% for the 0°/90° orientation and 6.4% for the 45°/-45° orientation. The addition of short fibers significantly increased porosity, with PLA-CF specimens presenting void contents of 8.3% for the 0°/90° orientation and 8.5% for the 45°/-45° orientation. Similarly, PLA-GF specimens displayed void contents of 7.9% and 8.1% for the 0°/90° and 45°/-45° orientations, respectively. The results suggest that fiber reinforcement increases the void percentage, which can be attributed to the difficulty in fully compacting the material during deposition. The presence of fibers affects the flow and adhesion of the molten polymer, potentially leading to microstructural discontinuities and interlayer gaps. Furthermore, the printing orientation had a minor influence on porosity levels, with a slight increase in void content for the 45°/-45° orientation across all materials. This trend aligns with findings from the literature, where diagonal raster angles tend to introduce more interlayer gaps due to variations in filament deposition and bonding efficiency. The higher porosity levels observed in fiber-reinforced composites highlight the necessity of adjusting printing parameters, such as extrusion temperature, deposition rate, and overlap between adjacent extrusions, to reduce void formation. Controlling these factors is essential for enhancing interfacial adhesion and improving the mechanical performance of 3D-printed composite structures. The results for Young’s modulus, as presented in Fig. 4 b, show clear differences between PLA, PLA-GF, and PLA-CF. For PLA, the values for the 0°/90° and 45°/-45° printing orientations were 2.7 GPa and 2.67 GPa, respectively. By comparison, the PLA-GF specimens exhibited lower values, with 2.17 GPa for the 0°/90° orientation and 2.14 GPa for the 45°/-45° orientation. PLA-CF specimens, however, showed the highest values, with 3.05 GPa for the 0°/90° orientation and 2.59 GPa for the 45°/-45° orientation. The higher Young's modulus for PLA-CF compared to both PLA and PLA-GF is expected due to the inherent stiffness of carbon fibers. Carbon fibers are known for their high modulus, which significantly contributes to the overall stiffness of the composite material [ 32 ]. This explains why PLA-CF exhibited the highest Young’s modulus values, particularly in the 0°/90° orientation, where the fibers are aligned with the load direction, thereby enhancing their contribution to the material’s stiffness. For PLA and PLA-GF, the lower values of Young’s modulus can be attributed to the lack of reinforcement in PLA and the lower stiffness of glass fibers in PLA-GF compared to carbon fibers. While glass fibers provide some reinforcement, they are not as rigid as carbon fibers, which explains why the PLA-GF specimens exhibited lower stiffness than PLA-CF [ 33 ]. Interestingly, the 45°/-45° printing orientation resulted in slightly lower Young’s modulus for all materials. This behavior is expected, as the fibers are diagonally oriented relative to the applied tensile load, reducing their ability to resist deformation directly and thereby lowering the modulus. This effect is more pronounced in PLA-CF, where the modulus dropped from 3.05 GPa in the 0°/90° orientation to 2.59 GPa in the 45°/-45° orientation, representing a decrease of approximately 15%. For PLA and PLA-GF, the decreases were much smaller, around 1.1% and 1.4%, respectively, reflecting the lower overall influence of fiber orientation on their mechanical performance. The results of tensile strength for different materials and printing orientations demonstrate distinct behaviors. For PLA, the maximum tensile strengths were 47.45 MPa in the 0°/90° orientation and 50.83 MPa in the 45°/-45° orientation. In the case of PLA-GF, the maximum tensile strengths were significantly lower, with values of 28.06 MPa for the 0°/90° orientation and 33.63 MPa for the 45°/-45° orientation. For PLA-CF, the values were 32.97 MPa for the 0°/90° orientation and 41.30 MPa for the 45°/-45° orientation. The observation that specimens printed in the 45°/-45° orientation exhibited higher maximum tensile strengths compared to the 0°/90° orientation can be attributed to the more effective distribution of stresses across the printed layers. According to Harshit et al. [ 37 ], tensile strength decreases with increasing printing angle. Specimens printed at a 0° angle exhibit layers aligned parallel to the tensile load direction, resulting in higher tensile strength. Conversely, specimens printed at a 45° angle are prone to shear failures, with layers fracturing at approximately 45°. Despite this, they can withstand greater loads compared to specimens printed at a 90° angle, where the load direction is perpendicular to the layer orientation, leading to reduced tensile strength [ 35 ]. In the 45°/-45° orientation, the diagonal arrangement of layers relative to the applied force allows for a more efficient distribution of stresses, thereby increasing resistance to deformation. This orientation may also enhance inter-layer bonding, resulting in superior adhesion and an increased capacity to withstand loads [ 36 ]. The results obtained for the Maximum Forces demonstrate distinct trends among the different materials and printing orientations. PLA specimens exhibited Maximum Forces of 2793.53 N in the 0°/90° orientation and 2944.69 N in the 45°/-45° orientation. These values indicate the superior performance of PLA, likely due to its homogeneity and the absence of reinforcements that could introduce weaknesses within the printed layers, such as porosity and adhesion issues between the PLA matrix and the fibers [ 38 ]. In comparison, the PLA-GF specimens showed Maximum Forces of 1616.03 N in the 0°/90° orientation and 1917.59 N in the 45°/-45° orientation. The reduction in Maximum Forces relative to PLA may be attributed to the characteristics of glass fibers, which, while providing some improvement in strength, are unable to match the structural integrity of PLA. Additionally, the presence of porosity and inferior adhesion between layers could have contributed to the decrease in strength [ 39 ]. The PLA-CF specimens exhibited Maximum Forces of 2087.25 N in the 0°/90° orientation and 2335.22 N in the 45°/-45° orientation. Although PLA-CF demonstrates superior performance compared to PLA-GF, it still falls short of PLA in both orientations. This can be explained by shear failure occurring within the fibers at angled printing orientations, as previously discussed. Furthermore, while the properties of carbon fibers are highly resistant, they may not be sufficient to surpass the mechanical characteristics of PLA, particularly concerning layer adhesion and the presence of porosity that could compromise strength [ 39 ]. Figure 5 presents the values of Young's modulus, maximum tensile strength, and maximum force obtained from the tensile test. The stress-strain curves provide valuable insights into the mechanical response of the different materials and printing orientations, showing how reinforcement type and raster angle influence the deformation behavior. For PLA, the strain values were 0.025 for the 0°/90° orientation and 0.027 for the 45°/-45° orientation. This 8% increase in strain suggests that printed layers deform more easily in the 45°/-45° orientation, where the layer arrangement relative to the applied force allows for greater elongation before failure. The 0°/90° orientation, however, results in a stiffer response, as the extruded layers align with the loading direction, improving resistance to tensile forces. For PLA-CF specimens, a reduction in strain was observed compared to PLA. The 0°/90° orientation exhibited a strain of 0.021, representing a 16% decrease relative to PLA. The presence of carbon fibers acts as a reinforcing agent, enhancing stiffness and consequently limiting material elongation. However, in the 45°/-45° orientation, the strain increased to 0.026, approaching the value observed for PLA in the same orientation. This 23.8% increase compared to the 0°/90° orientation suggests that, despite the reinforcing effect of the fibers, layer misalignment allows for greater elongation, similar to what was observed in PLA. The stiffest behavior was exhibited by PLA-GF specimens. Regardless of the printing orientation, the strain values remained constant at 0.016, indicating the lowest deformation capacity among all tested samples. The strain reduction was 36% compared to PLA with 0°/90° printing and 23% compared to PLA-CF in the same orientation. This behavior is attributed to the intrinsic rigidity of glass fibers, which effectively deformation. Additionally, the identical strain values between the two orientations suggest that the mechanical response of PLA-GF is dominated by the reinforcement, reducing the influence of raster angle on strain behavior. Despite the benefits of fiber reinforcement, the adhesion between fibers and the PLA matrix iinfluences mechanical properties. Weak interfacial bonding can lead to premature failure, as inadequate adhesion prevents efficient load transfer from the matrix to the fibers. This phenomenon is particularly relevant in fiber-reinforced composites, where poor adhesion results in pull-out effects and localized stress concentrations. Furthermore, porosity influences the mechanical behavior of 3D-printed composites. Insufficient bonding between deposited layers and improper fiber wetting can create voids, which act as stress concentrators, promoting crack nucleation and propagation. In a study by Nicolau et al. [ 38 ], PLA-GF specimens exhibited reinforcement distribution defects, including fiber agglomeration and matrix porosity, leading to inter and intra-layer delamination. Similar mechanisms could be responsible for the variations in mechanical properties observed in the present study. In FDM, adjusting extrusion temperature and deposition time is essential for enhancing inter-layer adhesion and reducing void formation. Rapid heating and cooling cycles can reduce crystallinity and alter the polymer's structural integrity, influencing the final mechanical properties [ 39 ]. Controlling the extrusion process reduces these effects and enhances the performance of fiber-reinforced composites. Figure 6 presents the fracture surfaces of the cross-sections of the tested specimens, highlighting the presence of voids and fiber distribution in PLA-GF and PLA-CF composites. These images provide insight into the interlayer adhesion and fracture mechanisms governing the mechanical performance of the materials. The cross-sectional fracture images (Fig. 6 ) reveal notable differences in void distribution and fiber dispersion between PLA-GF and PLA-CF specimens. These characteristics have a direct impact on mechanical performance, as confirmed by the mechanical property data. The presence of voids is more pronounced in PLA-CF specimens compared to PLA-GF, suggesting that fiber-matrix adhesion in PLA-GF is more effective. This behavior may be attributed to a more favorable interaction between the PLA matrix and glass fibers, as well as the processing temperature used during extrusion, which likely improved interlayer bonding and reduced porosity. In contrast, PLA-CF specimens exhibit a higher concentration of voids at the interlayer regions. The lower adhesion between carbon fibers and the PLA matrix may have hindered efficient stress transfer, leading to premature failure in tensile loading. This weaker bonding is consistent with the lower mechanical properties observed for PLA-CF when compared to PLA-GF. Additionally, the fracture surfaces of specimens printed at -45°/45° show fewer visible voids in the cross-section. However, this does not necessarily indicate a lower overall porosity in the printed structure. It is well established that this orientation tends to generate more voids due to the deposition pattern, but the fracture may preferentially propagate through regions with better adhesion, leaving void-rich areas less exposed. The 0°/90° orientation, on the other hand, appears to exhibit a more consistent interlayer structure. This configuration promotes better stress alignment along the printed layers, leading to higher mechanical resistance and delayed crack propagation. The mechanical data confirm this trend, with PLA-GF showing superior strength and modulus in this orientation compared to PLA-CF. The improved fiber-matrix interaction and reduced void content enhance stress transfer, increasing mechanical performance. Conversely, the higher porosity and weaker fiber-matrix bonding in PLA-CF reduce fracture resistance, leading to earlier failure. Furthermore, the dependence on print orientation is evident, as the 0°/90° orientation results in better load distribution, whereas − 45°/45° induces shear stresses that compromise interlayer adhesion. Figure 7 presents the SEM images of the fracture surfaces of PLA-CF and PLA-GF specimens after the tensile test. These images provide provide important insights into the failure mechanisms governing the fiber-reinforced composites, highlighting key aspects such as fiber-matrix adhesion, interfacial debonding, and fiber pull-out. For PLA-CF specimens (Fig. 6 a), the failure mode is primarily characterized by fiber-matrix debonding, evidenced by the widening of the fiber-matrix interface (debonding zone) before complete fiber extraction. This phenomenon occurs due to insufficient adhesion between the carbon fibers and the PLA matrix, leading to ineffective stress transfer. As a result, under tensile loading, the fibers detach from the matrix rather than breaking, leaving pull-out cavities in the fracture surface. This behavior is consistent with findings reported by Zhang et al. [ 32 ], who observed that weak interfacial bonding in carbon fiber-reinforced composites limits load transfer efficiency, thus reducing tensile strength. Conversely, for PLA-GF specimens (Fig. 6 b), the observed fracture surfaces exhibit fiber pull-out with cleaner fiber-matrix interfaces, suggesting a relatively stronger adhesion compared to PLA-CF. The presence of smaller debonding zones indicates a better stress distribution across the interface, which enhances mechanical performance. Studies by Li et al. [ 42 ] and Bian et al. [ 22 ] have shown that glass fibers typically establish better interfacial bonding with polymer matrices due to enhanced chemical compatibility, resulting in reduced fiber extraction and improved stress transfer. This difference in adhesion can explain the higher flexural strength of PLA-GF observed in the bending tests. Additionally, voids were identified in both composites, likely resulting from the detachment of fibers during tensile loading or incomplete impregnation during filament fabrication. These voids act as stress concentrators, further compromising mechanical properties. Türk et al. [ 16 ] emphasize that porosity and weak fiber-matrix interfaces are two primary factors that govern failure mechanisms in short-fiber-reinforced composites manufactured by FDM. The comparison between PLA-CF and PLA-GF reinforces the critical role of interfacial adhesion in dictating the mechanical response of fiber-reinforced composites. The more pronounced debonding effect in PLA-CF suggests a lower interfacial shear strength between the carbon fibers and PLA, whereas PLA-GF benefits from stronger fiber-matrix interactions. This observation aligns with previous studies on fiber-reinforced 3D-printed composites, which indicate that stronger interfacial bonding improves mechanical performance [ 13 ]. The fiber pull-out observed in PLA-CF, combined with extensive debonding regions, indicates limited stress transfer capability, leading to premature failure. Meanwhile, PLA-GF exhibits a more effective load transfer mechanism, reducing the likelihood of fiber detachment and enhancing mechanical integrity. To validate the statistical significance of the differences observed in mechanical performance, an analysis of variance (ANOVA) was conducted. This statistical approach was employed to assess the impact of reinforcement type and printing orientation on Young’s modulus, tensile strength, and maximum force. The ANOVA results, presented in Table 2 , provide insights into the relative contributions of these factors to the overall mechanical behavior of the specimens. A confidence level of 95% was applied, corresponding to a P-value threshold of 0.05, ensuring that only statistically significant differences were considered. Table 2 ANOVA Results – Tensile Test Source of variation Young's Modulus Tensile Strength Maximum Force F-Value P-Value F-Value P-Value F-Value P-Value Type of reinforcement 233.32 0.000 1568.7 0.000 21641 0.000 Printing orientation 45.88 0.000 240.4 0.000 35274 0.000 Type of reinforcement*Printing orientation 43.13 0.000 9.27 0.001 1567.7 0.000 R 2 96.15% 98.30% 98.99% Bold values indicate p < 0.05 The ANOVA results confirm that both the type of reinforcement and printing orientation have a statistically significant effect on the mechanical properties, as indicated by the low P-values (< 0.05) and high F-values. The interaction between reinforcement type and printing orientation was also significant, particularly for Young’s modulus (F = 43.13, P = 0.000) and maximum force (F = 1567.7, P = 0.000). This suggests that the impact of orientation is highly dependent on the type of reinforcement used. Notably, the R² values indicate that the model explains nearly all the variability in the data, particularly for tensile strength (98.30%) and maximum force (98.99%). These high values demonstrate that reinforcement type and printing orientation are the primary determinants of mechanical behavior in FDM-printed composites. 4.2 Four Bending Test Before the four-point bending tests, the void percentage of the printed specimens was evaluated. The results obtained were similar to those observed for the specimens intended for the tensile tests, with a variation of only 1.3%. The results of the four-point bending test are illustrated in Fig. 8 . The analysis focuses on the influence of fiber reinforcement and print orientation on the flexural properties of the specimens. The primary mechanical parameters evaluated include Flexural Modulus, Maximum Force, and Flexural Strength, providing insights into the stiffness and load-bearing capacity of the composites under bending loads. Following the ASTM D7264 standard, the tests were interrupted when the punch displacement reached 13 mm. In all specimens, no complete fracture was observed during testing, indicating that the materials exhibited high deformation capacity under bending conditions. The Flexural Modulus values obtained from the four-point bending test provide relevant information about the stiffness of the materials under flexural loads. For PLA, the Flexural Modulus was 0.98 GPa in the 0º/90° orientation and 1.04 GPa in the 45º/-45° orientation, showing a 6.12% increase for the 45º/-45° specimens. This small variation can be attributed to a more uniform stress distribution during bending in the 45º/-45° orientation, which slightly increases stiffness. However, the difference between the two orientations is relatively small, indicating that for PLA, print orientation has little effect on its flexural behavior [ 24 , 30 ]. In the case of PLA-GF, the Flexural Modulus was 1.15 GPa for the 0º/90° orientation and 1.01 GPa for the 45º/-45° orientation. Here, the 0º/90° orientation exhibits a higher Flexural Modulus, with an approximately 13.9% increase compared to the 45º/-45° orientation. This difference can be explained by the alignment of the glass fibers in the 0º/90° direction, which is more effective in bearing loads parallel to the fiber direction. Glass fibers, being relatively stiff, enhance the modulus when aligned with the load direction, which explains the higher values observed in the 0º/90° specimens. The 45º/-45° orientation introduces shear forces between fibers and matrix, resulting in a lower Flexural Modulus [ 31 , 33 ]. For PLA-CF, the Flexural Modulus was 1.13 GPa in the 0º/90° orientation and 1.08 GPa in the 45º/-45° orientation, with a 4.42% decrease for the 45º/-45° orientation. The smaller difference between the two orientations compared to the PLA-GF I suggests that carbon fibers contribute to maintaining stiffness even when subjected to multi-directional loads. This behavior is likely related to their load transfer characteristics of carbon fibers, which help retain a relatively high modulus even when the printing orientation introduces shear components [ 32 , 34 ]. The overall comparison of the materials highlights that both PLA-GF and PLA-CF demonstrate higher Flexural Modulus values than PLA, as expected due to the reinforcing effect of the fibers. However, the print orientation affects these materials differently. In PLA-GF, the modulus decreases in the 45º/-45° orientation, while PLA-CF shows a more consistent performance across both orientations. This behavior can be attributed to the superior mechanical properties and bonding behavior of carbon fibers compared to glass fibers, allowing for better stress distribution even in non-parallel orientations [ 28 , 35 ]. For PLA, the Maximum Force in the 0º/90° orientation was 975.46 N, while for the 45º/-45° orientation it was 882.57 N. This represents a 9.5% decrease in Maximum Force for the 45º/-45° specimens. The difference in Maximum Force between the two orientations can be attributed to the alignment of the layers relative to the applied load. In the 0º/90° orientation, the layers are better positioned to bear the applied stress, resulting in greater resistance to bending. In contrast, the 45º/-45° orientation, shear forces develop between the layers, weakening the structure and leading to earlier failure under bending loads [ 20 , 26 ]. In the case of PLA-GF, the Maximum Force was 1186.66 N in the 0º/90° orientation and 913.72 N in the 45º/-45° orientation, representing a 23% decrease in Maximum Force for the 45º/-45° orientation. This reduction can be explained by the fact that glass fibers are highly effective at reinforcing the material when aligned with the direction of the applied load, as in the 0º/90° orientation. In this orientation, the fibers are better positioned to support the bending forces, providing enhanced strength. In the 45º/-45° orientation, however, the load is applied at an angle to the fibers, reducing their ability to resist bending and leading to a lower Maximum Force [ 27 , 29 ]. For PLA-CF, the Maximum Force was 1000.84 N in the 0º/90° orientation and 906.06 N in the 45º/-45° orientation, resulting in a 9.4% decrease in the 45º/-45° orientation. The smaller difference in Maximum Force between the two orientations compared to PLA-GF suggests that carbon fibers are more capable of handling loads even when the layers are printed at an angle. This can be attributed to the superior load transfer properties of carbon fibers, which provide good reinforcement even in the 45º/-45° orientation. Nevertheless, the 0º/90° orientation still offers better performance, as the fibers are aligned to directly counteract the applied forces, providing greater resistance to bending [ 30 , 34 ]. For PLA, the flexural strength in the 0º/90° orientation was 14.32 MPa, while in the 45º/-45° orientation, it dropped to 13.23 MPa. This represents a 7.6% decrease in flexural strength when shifting from the 0º/90° to the 45º/-45° orientation. The alignment of the layers in the 0º/90° orientation allows the material to better withstand bending stresses, as the layers are oriented to carry the load effectively. Conversely, in the 45º/-45° orientation, shear forces come into play, reducing the effective strength of the material [ 22 , 28 ]. For PLA-GF, the flexural strength was 17.79 MPa in the 0º/90° orientation and decreased to 13.70 MPa in the 45º/-45° orientation, representing a 23% decrease. This reduction highlights the role of fiber alignment in load resistance. Glass fibers provide effective reinforcement when aligned with the load, enhancing composite’s strength. In the 45º/-45° orientation, the fibers are less aligned with the load, reducing their contribution to flexural strength [ 24 , 31 ]. For PLA-CF, the flexural strength for the 0º/90° orientation was 15.01 MPa, while for the 45º/-45° orientation, it decreased to 13.58 MPa. The smaller reduction in strength compared to PLA-GF suggests that carbon fibers still contribute to load transfer, even when their orientation does not fully align with the applied force [ 25 , 30 ]. The stress-strain curves obtained from the four-point bending tests describe the mechanical response of the materials under flexural loading. Figure 9 shows the average stress-strain behavior of PLA, PLA-GF, and PLA-CF specimens in both 0°/90° and 45°/-45° print orientations. These curves enable a comparative analysis of stiffness and yield behavior, showing the influence of fiber reinforcement and print direction on flexural performance. While these results provide an overall assessment of the materials’ mechanical response under bending loads, the ultimate failure mechanisms require additional fractographic analysis to be properly identified. For PLA, the strain measured at failure in the 0°/90° orientation was 0.046 mm/mm, while in the 45°/-45° orientation, it slightly decreased to 0.045 mm/mm. This small variation of approximately 2.17% suggests that printing orientation has a little influence on the flexural deformation of PLA, likely due to the lack of fiber reinforcement. Since the mechanical properties depend on the polymer matrix, the difference can be attributed to slight variations in stress distribution between the two orientations [ 24 , 30 ]. For PLA-GF, the strain values were 0.045 mm/mm for the 0°/90° orientation and 0.047 mm/mm for the 45°/-45° orientation, corresponding to a 4.26% increase in the 45°/-45° orientation. This trend can be explained by the orientation-dependent load transfer capacity of the glass fibers. In the 0°/90° orientation, the fibers are better aligned to bear the applied loads, leading to a stiffer response. In contrast, in the 45°/-45° orientation, the load is distributed along multiple directions, increasing the influence of the polymer matrix, which allows for slightly greater deformation before failure [ 31 , 33 ]. For PLA-CF, the strain at failure was 0.044 mm/mm in the 0°/90° orientation and 0.046 mm/mm in the 45°/-45° orientation, showing a 4.55% increase in strain for the latter configuration. The increase in strain in the 45°/-45° orientation can be attributed to the anisotropic nature of carbon fibers, which provide the highest stiffness when aligned with the loading direction. In the 0°/90° orientation, the fibers resist bending more effectively, reducing strain. However, in the 45°/-45° orientation, their contribution is reduced, allowing for greater deformation before failure [ 32 , 34 ]. Comparing the materials, PLA exhibited the highest strain values, followed by PLA-CF and PLA-GF. The lower deformation observed in PLA-GF specimens suggests that glass fibers restrict deformation more effectively than carbon fibers. This behavior is consistent with findings in the literature that emphasize the higher intrinsic stiffness of glass fibers compared to carbon fibers under flexural loads [ 28 , 35 ]. To statistically validate the effects of fiber reinforcement and printing orientation on the bending properties of the tested specimens, ANOVA was performed. The objective of this analysis is to determine whether the observed variations in Flexural Modulus, Flexural Strength, and Maximum Force are statistically significant or if they could be attributed to experimental variability. By applying ANOVA, it is possible to assess the individual contribution of each factor, as well as the interaction effects between fiber reinforcement and printing orientation, ensuring a comprehensive evaluation of the mechanical behavior of the composites. The results of the ANOVA are presented in Table 3 . Table 3 ANOVA Results – Four Bending Test Source of variation Flexural Modulus Flexural Strength Maximum Force F-value P-Value F-value P-Value F-value P-Value Type of reinforcement 1665.9 0.000 272.03 0.000 78.66 0.000 Print orientation 264.22 0.000 202.08 0.000 115.54 0.000 Type of reinforcement*Print orientation 72.2 0.000 155.09 0.000 42.3 0.000 R 2 99.36% 97.78% 93.71% Bold values indicate p < 0.05 The interaction effect between reinforcement type and printing orientation is particularly significant for Flexural Strength (F = 155.09) and Maximum Force (F = 42.3), indicating that the mechanical response of the material is not solely dependent on the individual factors, but also on how these parameters interact. This suggests that adjusting both fiber alignment and printing strategy is essential for enhancing mechanical performance. Additionally, the high R² values, such as 99.36% for Flexural Modulus and 97.78% for Flexural Strength, confirm that these variables account for most of the observed variance, emphasizing their importance in determining the mechanical properties of the material. 4.3 Fracture Toughness Test The analysis of fracture resistance in FDM-printed composites requires the evaluation of key parameters that influence crack initiation and propagation. The critical load (P Q ), the critical strain energy release rate (G IC ), and the fracture toughness (K IC ) provide a comprehensive understanding of the material's ability to resist mechanical failure. These parameters are essential for assessing the effect of fiber reinforcement and print orientation on fracture behavior. The values of P Q , G IC , and K IC were determined based on ASTM D5045-99, and the results are presented in Fig. 10 a, 10 b, and 10 c, respectively. The P Q results complement the G IC and K IC findings, demonstrating the influence of fiber reinforcement and printing orientation on fracture resistance. Specimens printed in the 0°/90° orientation exhibited higher P Q values than those in the 45°/-45° orientation, confirming the role of layer alignment in fracture resistance. The 0°/90° configuration improves load transfer and stress redistribution, delaying crack propagation. In contrast, the 45°/-45° orientation induces higher interlaminar shear stresses, reducing fracture resistance. For PLA, the P Q values were 1223.63 N for 0°/90° and 862.52 N for 45°/-45°, 29.5% decrease. This suggests that layer bonding in the 0°/90° orientation better resists fracture. Since PLA no fiber reinforcement, its fracture behavior depends mainly on interlayer adhesion, which is more susceptible to stress concentration when loaded at oblique angles. For PLA-GF, the P Q values were 1186.66 N for 0°/90° and 930.12 N for 45°/-45°, showing a 21.6% reduction. This difference highlights the importance of fiber orientation in improving load-bearing capacity. When glass fibers are aligned with the principal loading direction, they act as effective barriers to crack propagation. However, in the 45°/-45° orientation, the misalignment of fibers leads to reduced energy dissipation and lower fracture resistance, reinforcing observations previously reported for fiber-reinforced polymer composites. For PLA-CF, the P Q values were 1002.83 N for 0°/90° and 897.66 N for 45°/-45°, reflecting a 10.5% decrease. The smaller difference suggests that carbon fibers provide some degree of fracture resistance even when fiber alignment is less favorable. The higher stiffness of carbon fibers may contribute to stress redistribution, reducing localized stress concentrations and delaying crack propagation. The G IC values, which represent the material’s energy absorption capacity before crack propagation, followed the same trend. The 0°/90° orientation consistently showed higher GIC values than the 45°/-45° orientation, confirming that fiber alignment improves stress transfer and delays crack initiation. For PLA, the G IC was 10.31 kJ/m² in the 0°/90° orientation and 4.70 kJ/m² in the 45°/-45° orientation, a 54.4% reduction. The lower GIC in the 45°/-45° orientation suggests that cracks propagate more easily due to weaker interlayer adhesion and higher shear stresses at misaligned layer interfaces. For PLA-GF, the G IC was 7.98 kJ/m² for the 0°/90° orientation, decreasing to 5.64 kJ/m² in the 45°/-45° orientation, a 29.3% reduction. This reduction highlights the role of fiber alignment in energy dissipation. When glass fibers are aligned with the loading direction, they act as crack barriers, requiring more energy for fracture initiation. In the 45°/-45° orientation, fiber misalignment reduces their reinforcing effect, leading to lower energy absorption. For PLA-CF, the G IC values were 5.84 kJ/m² in the 0°/90° orientation and 4.88 kJ/m² in the 45°/-45° orientation, a 16.4% reduction. Compared to PLA-GF, this smaller decrease suggests that carbon fibers contribute to fracture resistance even when fiber alignment is not ideal. The higher stiffness of carbon fibers may facilitate stress redistribution, reducing localized stress concentrations and slowing crack propagation. The K IC values, which represent fracture toughness, followed the same trend, with higher values in the 0°/90° orientation across all materials. This behavior is attributed to layer and fiber alignment with the loading direction, improving stress transfer and reducing stress concentrations at interlayer regions. For PLA, the K IC was 3.13 MPa·m¹/² in the 0°/90° orientation and 2.20 MPa·m¹/² in the 45°/-45° orientation, a 29.5% reduction. This suggests that interlayer adhesion is more effective in the 0°/90° orientation, improving stress redistribution and fracture resistance. For PLA-GF, the K IC was 3.03 MPa·m¹/² in the 0°/90° orientation and 2.37 MPa·m¹/² in the 45°/-45° orientation, a 21.6% reduction. This result reinforces the role of fiber alignment in distributing applied stresses, as glass fibers oriented with the principal stress direction improve fracture resistance. Misaligned fibers in the 45°/-45° orientation reduce the material’s ability to withstand crack propagation. For PLA-CF, the K IC was 2.56 MPa·m¹/² in the 0°/90° orientation and 2.29 MPa·m¹/² in the 45°/-45° orientation, a 10.5% decrease. Compared to PLA-GF, this smaller difference suggests that carbon fibers enhance fracture resistance even in less favorable alignments. However, their weaker interfacial adhesion with the PLA matrix may explain the lower K IC values compared to PLA-GF. Table 4 presents the results of the ANOVA for P Q , G IC , K IC , obtained from the fracture toughness test. The analysis revealed P-values lower than 0.05, indicating statistically significant differences in fracture toughness values among the tested materials and printing orientations. Table 4 ANOVA results for critical load (PQ), critical strain energy release rate (GIC), and fracture toughness (KIC) from fracture toughness tests - PLA, PLA-CF, and PLA-GF Source of variation P Q G IC K IC F-value P-Value F-value P-Value F-value P-Value Type of reinforcement 214.54 0.002 237.03 0.020 260.8 0.000 Print orientation 838.9 0.000 885 0.000 754.97 0.000 Type of reinforcement*Print orientation 57.77 0.000 60.47 0.000 109.8 0.000 R 2 94.05% 97.78% 98.42% Bold values indicate p < 0.05 The ANOVA results confirm that both reinforcement type and printing orientation influence fracture resistance across all analyzed parameters (P Q , G IC , and K IC ). Printing orientation had the greatest effect, as indicated by high F-values (F PQ =838.9, F GIC =885.0, F KIC =754.97, P < 0.05), reinforcing the role of layer alignment and fiber orientation in fracture behavior. Crack propagation resistance depends on how stress is distributed along the printed layers, a well-documented phenomenon in anisotropic materials. Reinforcement type also played a statistically significant role (F PQ =214.54, F GIC =237.03, F KIC =260.8, P < 0.05), confirming that fiber inclusion directly affects the mechanical performance of PLA composites. Among the tested materials, PLA-GF exhibited the highest fracture toughness (K IC ) and strain energy release rate (G IC ), highlighting the beneficial effect of glass fibers in improving crack resistance through enhanced fiber-matrix load transfer. PLA-CF, however, showed more consistent performance across orientations, suggesting that carbon fibers contribute to fracture resistance even in less favorable layer alignments. The interaction between reinforcement type and printing orientation was also significant (F PQ =57.77, F GIC =60.47, F KIC =109.8, P < 0.05), indicating that these factors influence each other in determining fracture behavior. This interaction was particularly strong for GIC, where printing orientation had the most pronounced effect. The high R² values (R² PQ =94.05%, R² GIC =97.78%, R² KIC =98.42%) confirm that the tested factors explain nearly all observed variations in fracture resistance. These results align with previous studies, such as Zhang et al. [ 32 ], who reported that fiber-reinforced composites exhibit enhanced fracture resistance when fibers are aligned with the principal stress direction. Similarly, Rajpurohit et al. [ 44 ] found that anisotropic behavior induced by layer orientation strongly affects fracture performance. The superior K IC and G IC values observed in the 0°/90° orientation across all materials indicate that stress redistribution is more efficient when fibers and layers align with the applied force, improving fracture toughness. PLA-GF exhibited higher K IC and G IC than PLA-CF in this orientation, likely due to stronger interfacial bonding between glass fibers and the PLA matrix. Conversely, despite their high stiffness, carbon fibers may have weaker adhesion with the polymer matrix, potentially reducing crack resistance in certain orientations. The fracture analysis provides further insights into the failure mechanisms of PLA composites reinforced with carbon and glass fibers. Figure 11 illustrates the fracture behavior of PLA-CF and PLA-GF specimens in both 0°/90° and 45°/-45° orientations. For PLA-CF specimens, fracture initiation occurred at the inner and outer radii of the notch curvature (Figs. 11 a and 11 ), with the most pronounced fracture zone at the inner radius, where stress levels were highest due to the bending moment. Microscopic analysis (Fig. 11 c) shows carbon fibers aligned with the tensile stress direction, suggesting a stress-induced fracture mechanism. This observation supports the findings of Rajpurohit et al. [ 44 ], who reported that stronger interlayer adhesion in the 0°/90° orientation contributes to higher flexural strength. In contrast, PLA-GF specimens exhibited a different fracture pattern (Figs. 10 d and 10 e). Fracture initiation was observed at the point of maximum force application, with crack propagation occurring more uniformly along the interlayer regions. The concentration of tensile stresses near the fracture region suggests better interlayer bonding in PLA-GF compared to PLA-CF. Microscopic analysis (Fig. 10 f) further supports this observation, showing fractured glass fibers aligned with the applied load, indicating more effective load transfer. The stronger fiber-matrix interface in PLA-GF likely enhances crack bridging, contributing to improved fracture toughness. Additionally, specimens printed in the 0°/90° orientation consistently exhibited higher fracture resistance than those printed in 45°/-45°. This trend aligns with studies demonstrating that layer alignment parallel to the bending plane enhances resistance to flexural loads [ 39 ]. Failure initiation typically occurred on the tensile side of the specimen, but compressive forces counteracted crack propagation, preserving layer cohesion and improving overall structural integrity. These results reinforce the role of fiber alignment, interlayer adhesion, and fiber-matrix load transfer in governing the fracture resistance of FDM-printed composites, highlighting the importance of printing orientation and reinforcement selection in enhancing mechanical performance under bending conditions. 4. Conclusions This study analyzed the influence of short carbon and glass fiber reinforcement, as well as print orientation, on the mechanical properties, fracture behavior, and thermal stability of FDM-printed PLA composites. The results indicate that both fiber type and raster orientation significantly affect the structural integrity of the printed specimens. Tensile tests demonstrated that PLA specimens printed in the 45°/-45° orientation exhibited the highest tensile strength, reaching 50.83 MPa. This behavior suggests that diagonal raster orientations enhance load distribution, reducing stress concentration under uniaxial loading. In contrast, flexural tests revealed that PLA-GF specimens with a 0°/90° print orientation achieved the highest flexural strength (17.79 MPa), representing a 24.23% increase compared to pure PLA. The alignment of glass fibers with the primary stress direction contributed to enhanced load transfer efficiency and flexural resistance. The fracture toughness analysis showed that the 0°/90° orientation resulted in higher K IC values across all materials, reinforcing the role of fiber and layer alignment in crack propagation resistance. The higher fracture toughness of PLA-GF compared to PLA-CF suggests that glass fibers promote stronger interfacial adhesion, leading to improved energy dissipation during fracture. Fractographic analysis confirmed that fiber pull-out and interfacial debonding were the predominant failure mechanisms in fiber-reinforced composites, demonstrating the critical influence of fiber-matrix interaction on the mechanical response. Porosity analysis revealed that fiber-reinforced composites exhibited higher void content, which negatively affected both tensile and flexural performance. This finding highlights the importance of adjusting printing parameters, such as extrusion temperature and raster orientation, to reduce void formation and enhance interlayer bonding. TGA confirmed that PLA-CF exhibited higher thermal stability than PLA-GF, suggesting that carbon fiber reinforcement improves the resistance of PLA composites to thermal degradation. Additionally, the fiber content obtained through TGA closely matched the manufacturer’s nominal values, confirming the uniform dispersion of fibers within the polymer matrix. The results demonstrated that both fiber reinforcement and printing orientation significantly influence the mechanical and fracture behavior of FDM-printed PLA composites. The 0°/90° orientation consistently resulted in higher P Q , K IC and G IC values, indicating superior fracture resistance due to enhanced stress redistribution and fiber-matrix load transfer. Among the tested materials, PLA-GF exhibited the highest K IC 3.03 MPa·m¹/² and G IC 7.98 kJ/m²), while PLA-CF showed the lowest reduction in fracture resistance between orientations, suggesting a more stable performance under different loading conditions. Declarations Acknowledgments The authors would like to thank the Postgraduate Program in mechanical Engineering of the Federal University of Minas Gerais (UFMG), Brazil, for the provision of laboratory facilities. Funding This work was partly financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)–Finance Code 001. Also, it must be acknowledged the financial support of the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG). Data availability: The authors confirm that the data supporting the findings of this study are available within the article. Ethics approval and consent to participate All authors have previously approved this paper and judged that there is no ethical infringement. Consent to participate and publication All authors would like to declare that they have approved their participation and consent about the publication in this journal. Competing interests The authors declare no competing interests. Contributions Frederico de Castro Magalhaes: conceptualization, data curation, formal analysis, investigation, methodology, review and editing, validation. Pilar Fabra Rivera: conceptualization, data curation, formal analysis, investigation, methodology, writing — original draft, writing-review and editing. Juan Campos Rubio: data curation, conceptualization, methodology, resources, supervision, writing-review and editing. 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Polymers, 12(7), 1529. https://doi.org/https://doi.org/10.3390/polym12071529. Prajapati, A; Dave, H; Raval, H. (2021). Effect of fiber volume fraction on the impact strength of fiber reinforced polymer composites made by FDM process. Materials today proceedings, 44, 2102-2106. https://doi.org/https://doi.org/10.1016/j.matpr.2020.12.262. Hofstatter, T; B Pedersen, D; Tosello, G; N Hansen, H. (2017). State-of-the-art of fiber-reinforced polymers in additive manufacturing technologies. Journal of Reinforced Plastics, 36(15), 1061–1073. https://doi.org/10.1177/0731684417695648. Akhoundi B, Behravesh AH, Bagheri Saed A. (2019). Improving mechanical properties of continuous fiber-reinforced thermoplastic composites produced by FDM 3D printer. Journal of Reinforced Plastics and Composites, 38(3), 99-116. https://doi.org/https://doi.org/10.1177/07316844188073 Ismail, K; Yap, T; Ahmed, R. (2022). 3D-Printed Fiber-Reinforced Polymer Composites by Fused Deposition Modelling (FDM): Fiber Length and Fiber Implementation Techniques. Polymers, 14(21), 4659. https://doi.org/https://doi.org/10.3390/polym14214659. Parmiggiani, A; Prato, M; Pizzorni, M. (2021). Effect of the fiber orientation on the tensile and flexural behavior of continuous carbon fiber composites made via fused filament fabrication. The International Journal of Advanced Manufacturing Technology, 114, 2085–2101. https://doi.org/https://doi.org/10.1007/s00170-021-06997-5. Agarwal, S., Shukla, M., & Kumar, S. (2022). Effect of fiber loading on the mechanical performance of 3D-printed fiber-reinforced composites. Composite Structures, 283, 115234. Li, J; Yvonne, D; Huang, X; Sun, G; Ruan, D. (2022). Additively manufactured fiber-reinforced composites: A review of mechanical behavior and opportunities. Journal of Materials Science & Technology, 119, 219-244. https://doi.org/https://doi.org/10.1016/j.jmst.2021.11.063. Zhang, H; Yang, D; Sheng, Y. (2018). Performance-driven 3D printing of continuous curved carbon fibre reinforced polymer composites: A preliminary numerical study. Composites Part B, 151, 256-264. https://doi.org/https://doi.org/10.1016/j.compositesb.2018.06.017 Zhuang, Y.; Zou, B.; Ding, S.; Wang, P. (2022). Shear and Tensile Behaviors of Fiber-Reinforced Resin Matrix Composites Printed by the FDM Technology . Coatings, 12(7), 1000. https://doi.org/https://doi.org/10.3390/coatings12071000. Mohankumar, H.R; Gundappa, M; Pradeepkumar, G; Tambrallimath, S; Ramaia. K; Yunus, M; Bhutto, J; Mohammed, A. (2023). Effect of Short Glass Fiber Addition on Flexural and Impact Behavior of 3D Printed Polymer Composites. ACS Omega, 8(10), 9212–9220. https://doi.org/10.1021/acsomega.2c07227 Kumar, L; Nair, K. (2017). Current Trends of Additive Manufacturing in the Aerospace Industry. Advances in 3D Printing & Additive Manufacturing Technologies, 39-54. https://doi.org/https://doi.org/10.1007/978-981-10-0812-2_4 Mohammadizadeh, M; Imeri, A; Fidan, I; Elkelany, M. (2019). 3D printed fiber reinforced polymer composites - Structural analysis. Composites Part B: Engineering, 175, 107112. https://doi.org/10.1016/j.compositesb.2019.107112 Harshit K, Dave R, Prajapati R, Rajpurohit H, Patadiya K, Raval. (2022). Investigation on tensile strength and failure modes of FDM printed part using in-house fabricated PLA filament. Advances in Materials and Processing Technologies, 8, 576-597. Nicolau, A; Pop, A; Coșereanu, C. (2022). 3D Printing Application in Wood Furniture Components Assembling. Materials, 15(8), 2907. https://doi.org/https://doi.org/10.3390/ma15082907 Li, N., Li, Y., & Liu, S. (2020). Rapid prototyping of continuous fiber reinforced composites via fused deposition modeling: Material characterization and structure optimization. Materials & Design, 186, 108248. Agarwal, S., Shukla, M., & Kumar, S. (2022). Effect of fiber loading on the mechanical performance of 3D-printed fiber-reinforced composites. Composite Structures, 283, 115234 . Torrado, A. R., Roberson, D. A. (2016). Failure analysis and anisotropy evaluation of 3D-printed tensile test specimens of different geometries and print raster patterns. Journal of Failure Analysis and Prevention, 16, 1, 154-164. Ahn, S. H., Montero, M., Odell, D., Roundy, S., & Wright, P. K. (2002). Anisotropic material properties of fused deposition modeling ABS. Rapid Prototyping Journal, 8, 4, 248-257. Spoerk, M., Gonzalez-Gutierrez, J., Sapkota, J., Schuschnigg, S., & Holzer, C. (2018). Effect of the printing bed temperature on the adhesion of parts produced by fused filament fabrication. Additive Manufacturing, 24, 57-62 . Rajpurohit, S.R.; Dave, H.K. (2018). Flexural strength of fused filament fabricated (FFF) PLA parts on an open-source 3D printer. Advances in Manufacturing, 6, 430-441. https://doi.org/https://doi.org/10.1007/s40436-018-0237-6 Cite Share Download PDF Status: Published Journal Publication published 16 Oct, 2025 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted Editorial decision: Minor Revisions Needed 04 Oct, 2025 Reviewers agreed at journal 14 Aug, 2025 Reviewers invited by journal 14 Aug, 2025 Editor assigned by journal 14 Aug, 2025 First submitted to journal 12 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7336068","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":500542904,"identity":"06373208-63e3-4eb0-883d-e1fab92e9981","order_by":0,"name":"Frederico de Castro Magalhães","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Frederico","middleName":"de Castro","lastName":"Magalhães","suffix":""},{"id":500542905,"identity":"1a8e98c0-876d-4f24-b38a-69f124d4deab","order_by":1,"name":"Andrea Del Pilar Fabra Rivera","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Andrea","middleName":"Del Pilar Fabra","lastName":"Rivera","suffix":""},{"id":500542906,"identity":"c3a3f67b-e441-4bc1-a409-2cc637f5094b","order_by":2,"name":"Juan Carlos Campos Rubio","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAoElEQVRIiWNgGAWjYBACxgYg8YFBDkjykKCFcQaDMQlaQICZhyQtzDOSnz22bTOIlnfgPfaBOIfNSDM3zm0zyN14gC95BpFaEsykc9v+5G5s4DEmzmGMM9K/SVuCbCFBS46ZNCNQy3wGorX0vCmT7DlnkLuBmS+ZOC2G7enbJH6UAW1p7z1MpJYGKMOASA0MDPJwRgMeVaNgFIyCUTCyAQDzCCor4+Vv5wAAAABJRU5ErkJggg==","orcid":"","institution":"Universidade Federal de Minas Gerais","correspondingAuthor":true,"prefix":"","firstName":"Juan","middleName":"Carlos Campos","lastName":"Rubio","suffix":""}],"badges":[],"createdAt":"2025-08-09 22:56:00","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7336068/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7336068/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00170-025-16794-z","type":"published","date":"2025-10-16T15:57:15+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":89673837,"identity":"026b697d-6908-4fe6-94b0-cde1136d82bd","added_by":"auto","created_at":"2025-08-22 13:22:03","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":92291,"visible":true,"origin":"","legend":"\u003cp\u003eResearch plan flowchart detailing the study steps.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/6926f965b81a166d66c4a7ef.png"},{"id":89673836,"identity":"b75d2a1c-5bd2-42d9-a0da-e658e8f12d78","added_by":"auto","created_at":"2025-08-22 13:22:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":76037,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Specimen design for tensile testing and b. specimen design for the four-point bending test.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/349926e3ea822ffed9dcf430.png"},{"id":89673844,"identity":"118f4606-6654-404d-8d19-79b27ea82c70","added_by":"auto","created_at":"2025-08-22 13:22:03","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":343123,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Thermogravimetric analysis results for PLA, PLA-CF and PLA-GF. (b) Microstructure - Short carbon fibers in PLA matrix and (c) Microstructure - Short glass fibers in PLA matrix.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/8abe1a6df8ad99830e5260a5.png"},{"id":89674917,"identity":"7b7c8f99-e3ab-482a-8743-8e7ab83c64aa","added_by":"auto","created_at":"2025-08-22 13:30:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":107206,"visible":true,"origin":"","legend":"\u003cp\u003eTensile test results PLA, PLA-CF, and PLA-GF specimens manufactured with 0°/90° and 45°/-45° printing orientation. (a) Voids (b) Young’s Modulus (c) Tensile strength and (d) Maximum Force.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/4347009a0fa16ac9def41cf7.png"},{"id":89673839,"identity":"6a5ef725-7572-4e02-8727-c729ad25c7be","added_by":"auto","created_at":"2025-08-22 13:22:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":28291,"visible":true,"origin":"","legend":"\u003cp\u003eTensile stress-strain curves for the manufactured specimens from PLA, PLA-GF, and PLA-CF with 0°/90° and 45°/-45° printing orientation.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/7e76585836ce340c0ef0864a.png"},{"id":89677351,"identity":"5ea3af5f-2c7b-4828-b0db-7f1b1cd45e6a","added_by":"auto","created_at":"2025-08-22 13:54:03","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":805023,"visible":true,"origin":"","legend":"\u003cp\u003eFracture surfaces of the cross-sections of the tested specimens: a) PLA 0º/90º, b) PLA 45º/-45º, c) PLA- GF 0º/90º, d) PLA-GF 45º/-45º, e) PLA- CF 0º/90º and f) PLA-CF 45º/-45º.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/8120a7f0b3ef2a978d063ae5.png"},{"id":89674921,"identity":"6e4a9c10-3c6d-43cf-8d27-ae1e573bfd2d","added_by":"auto","created_at":"2025-08-22 13:30:03","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":232073,"visible":true,"origin":"","legend":"\u003cp\u003eFracture microstructure of tested specimens: \u0026nbsp;a) PLA-CF and b) PLA-GF specimens - Tensile test.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/837a78207ecf455fc8d30c66.png"},{"id":89674925,"identity":"dc8c081a-634a-4f3d-b5b5-a00c1a19a2c6","added_by":"auto","created_at":"2025-08-22 13:30:03","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":51170,"visible":true,"origin":"","legend":"\u003cp\u003eFour-point bending test results for the manufactured specimens from PLA, PLA-CF, and PLA-GF at 0°/90° and 45°/-45° printing orientation. (a) Flexural Modulus (b) Maximum Force and (c) Flexural strength.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/e693a32051abeedd120ca0ca.png"},{"id":89676288,"identity":"65f6dd20-8bf4-4012-ad30-e9e0b2703787","added_by":"auto","created_at":"2025-08-22 13:46:03","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":22604,"visible":true,"origin":"","legend":"\u003cp\u003eFour-point bending stress-strain curves for the manufactured specimens from PLA, PLA-CF, and PLA-GF at 0°/90° and 45°/-45° print orientation.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/f8af6858ed05fc9785f56144.png"},{"id":89674929,"identity":"b8b93839-80d3-41cb-9f9f-fd50392dc4fa","added_by":"auto","created_at":"2025-08-22 13:30:04","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":44386,"visible":true,"origin":"","legend":"\u003cp\u003eResults from fracture toughness tests performed according to ASTM D5045-99 standard. (a) Critical load (PQ), (b) critical strain energy release rate (GIC), and (c) fracture toughness (KIC) for PLA, PLA-CF and PLA-GF, considering two different print orientations (0°/90° and 45°/-45º).\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/1bdcc94295359e804399fcc4.png"},{"id":89674924,"identity":"3ac79442-4da9-44e9-8ae3-94b297b1193a","added_by":"auto","created_at":"2025-08-22 13:30:03","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":467180,"visible":true,"origin":"","legend":"\u003cp\u003eOptical microscopy images showing fracture zones in notched specimens subjected to fracture toughness tests: (a) PLA-CF (0°/90°), (b) PLA-CF (45º/-45º), (c) Detail of short carbon fibers aligned with tensile stress direction in PLA-CF; (d) PLA-GF(0°/90°), (e) PLA-GF (45°/-45º) and (f) Detail of short glass fibers dispersed within the PLA matrix.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/437ebaccfa9e95eda177fff5.png"},{"id":93956069,"identity":"a32b3a80-7b84-47dc-9e22-3ac8bdddfa67","added_by":"auto","created_at":"2025-10-20 16:10:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3270112,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7336068/v1/5e2f02c6-f685-418a-b08a-4110b4191e6a.pdf"}],"financialInterests":"","formattedTitle":"Influence of Short Carbon and Glass Fibers on the Mechanical Performance, Thermal Stability, and Fracture Behavior of FDM-Printed Composites","fulltext":[{"header":"1. INTRODUCTION","content":"\u003cp\u003eFused Deposition Modeling (FDM) is one of the most widely used techniques in additive manufacturing for reconstructing parts, enabling the three-dimensional production of components from designs created in Computer-Aided Design (CAD) software. This process has been extensively studied due to its versatility and applicability in various fields [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. During the FDM process, material is deposited layer by layer onto the printer bed, following pre-defined instructions set in a G-code file, ensuring precise geometric reproduction [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe FDM technique offers several advantages, including the ability to produce complex designs, cost-effectiveness, short lead times, and repeatability. As noted by John et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and C\u0026oacute;zar et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], these benefits have led to its adoption in the medical, aerospace, automotive, and engineering industries. Conventional manufactured parts can be replaced by lighter and more flexible components, thereby reducing energy consumption and material waste in the aerospace industry [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. However, despite these advantages, FDM-printed parts exhibit mechanical limitations when compared to conventionally manufactured components, mainly due to their layer-by-layer structure, which introduces anisotropy and interlayer defects [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOtherwise, Ponticelli et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] proposed the replacement of conventional aluminium-made brackets for overhead locker within commercial aircrafts by manufactured composite PEEK-Carbon fibres (10%) using FDM technology. The authors showed that it was possible to identify a reduction, not only in the production costs, but also on environmental impacts associated with aviation area, improve sustainability of sector.\u003c/p\u003e\u003cp\u003eHernandez et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and Agarwal et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] reported that the mechanical properties of parts manufactured using FDM technology differ from those produced through conventional processes. Studies show that the tensile strength of FDM-printed parts can be between 10% and 73% lower than that of injection-molded counterparts, due to intrinsic voids and weak interlayer adhesion [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Mei et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e] and Dong et al. [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e] highlight that the presence of voids and gaps between layers is a primary factor contributing to these decreased mechanical properties. T\u0026uuml;rk et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] and Geng et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] attribute the source of these voids and gaps to factors such as inadequate printing parameters, limitations in stepper motor precision, and material deposition settings, which directly impact part performance. Therefore, adjusting the printing parameters and selecting appropriate reinforcement strategies contribute to enhancing the structural integrity of FDM parts.\u003c/p\u003e\u003cp\u003eFurthermore, Ding et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] and Maqsood et al. [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] note that the material extruded using the FDM technique cools rapidly from the glass transition temperature to ambient temperature. This rapid cooling generates internal stresses that can reduce interlayer adhesion, leading to crack formation, delamination, and anisotropic mechanical behavior. Studies show that flexural strength can be reduced by up to 40% due to these effects [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Gao et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] and Adeniran et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] reinforce that these factors impact both inter- and intralaminar deformation, reducing the mechanical properties considerably. To address these issues, researchers have explored alternative solutions such as modifying processing parameters, improving adhesion techniques, and incorporating fiber reinforcements to counteract weaknesses inherent to FDM-printed structures [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAccording to Bian et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] and Shah et al. [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], several studies are currently underway to analyze and comprehend the mechanical behavior of parts manufactured using the FDM technology. Wickramasinghe et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] and Prajapati et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] indicate that mechanical performance can be improved by adjusting printing parameters, annealing, snap-fitting, printing in an oxygen-free environment, mechanical pressing, and the use of fiber-reinforced polymer composites. These methods have demonstrated effectiveness in reducing void content and enhancing interlayer adhesion, contributing to increased mechanical strength and dimensional stability. For example, annealing has been shown to increase tensile strength by up to 20% and improve interlayer bonding, while adjusting raster orientation and infill density can lead to an increase of up to 30% in Young\u0026rsquo;s modulus [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. However, while significant advancements have been made in adjusting FDM parameters, the role of fiber reinforcement in overcoming anisotropic effects and void formation requires further investigation.\u003c/p\u003e\u003cp\u003eAmong the available polymer matrices for additive manufacturing, polylactic acid (PLA) stands out due to its ease of processing, biodegradability, and good mechanical performance relative to other thermoplastics used in FDM [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. However, PLA exhibits inherent brittleness and low impact resistance, limiting its applicability in structural components [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. To enhance the mechanical properties of PLA while maintaining its printability, reinforcement with short fibers has been explored as a viable approach. Short carbon and short glass fibers were selected as reinforcements in this study due to their ability to significantly improve stiffness, strength, and thermal stability without the challenges associated with continuous or long fibers, such as poor dispersion and excessive viscosity during extrusion [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHofstatter et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] and Akhoundi et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] note that fiber-reinforced polymer composites are well-known for their high stiffness, mechanical strength, fatigue resistance, and corrosion resistance. Ismail et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] reported that short carbon fiber reinforced polymer composites fabricated via FDM can achieve tensile strengths of up to 67 MPa and Young\u0026rsquo;s moduli around 8.4 GPa, depending on fiber weight percentage and processing conditions [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Parmiggiani et al. [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] emphasize that fiber orientation plays a critical role in mechanical performance, with continuous fiber composites achieving tensile strengths as high as 800 MPa when fibers are aligned in the load direction, whereas short fiber-reinforced composites typically range between 150 MPa and 400 MPa.\u003c/p\u003e\u003cp\u003ePrevious studies have shown that fiber content above 40 wt% can lead to percolation effects, causing significant flow issues, nozzle clogging, and poor layer adhesion [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Thus, a reinforcement level of 20 wt% was chosen to ensure processability while maintaining improvements in mechanical properties. Li et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] reported that this reinforcement percentage leads to a significant increase in tensile modulus while preserving print quality. However, the relationship between moderate fiber content (20 wt%) and print orientation remains underexplored, despite its relevance in achieving a compromise between printability and mechanical performance in FDM composites.\u003c/p\u003e\u003cp\u003eZhang et al. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] report that incorporating fibers into a polymer matrix reduces stress concentration and increases stiffness. This behavior is typical of fiber-reinforced composites, where the fibers\u0026rsquo; lower ductility compared to the polymer matrix limits deformation before fracture. Short carbon fibers (PLA-CF) typically have lengths between 100\u0026ndash;400 \u0026micro;m and diameters ranging from 7\u0026ndash;13 \u0026micro;m, with optimal reinforcement effects observed for fibers around 150 \u0026micro;m [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Short glass fibers (PLA-GF) in 3D-printed composites often range from 200\u0026ndash;400 \u0026micro;m in length, with a diameter of approximately 10 \u0026micro;m, improving impact resistance by up to 54% compared to pure polymer matrices [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAlthough fiber-reinforced FDM composites have been extensively studied, most research has focused on individual parameters such as raster angle or fiber content, without considering their combined effects. Moreover, previous studies have primarily investigated continuous fiber composites or higher fiber loadings (\u0026gt;\u0026thinsp;30 wt%), which can introduce processability challenges such as increased viscosity, extrusion difficulties, and nozzle clogging, ultimately compromising layer adhesion and print quality [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Therefore, further research is needed to systematically evaluate moderate fiber reinforcement levels under different printing orientations to better understand their impact on mechanical performance.\u003c/p\u003e\u003cp\u003eTo address the existing knowledge gaps in the additive manufacturing of fiber-reinforced composites, this study evaluates the mechanical behavior of FDM-printed thermoplastic composites reinforced with short glass and carbon fibers. Commercially available PLA-CF and PLA-GF filaments with nominal fiber dimensions (160 \u0026micro;m length, 13 \u0026micro;m diameter) and a stated reinforcement percentage of 20 wt%, as provided by the manufacturer, ensuring consistency in material properties while maintaining good extrudability. The effect of print orientation (0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg;) is analyzed, as raster angle variations significantly influence mechanical performance, particularly in fiber-reinforced composites [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Comparative analyses between PLA, PLA-CF, and PLA-GF are conducted to quantify the impact of fiber type and orientation on tensile strength, four-point bending strength, and fracture toughness, providing insights into how fiber alignment and interlayer adhesion affect mechanical response. By examining these variables, this study aims to provide a broader understanding of the mechanical behavior of fiber-reinforced FDM composites, supporting improved material selection and printing strategies for high-performance applications.\u003c/p\u003e"},{"header":"2. MATERIALS AND METHODS","content":"\u003cp\u003eTo achieve the proposed objectives, a structured research plan was established, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, which presents the flowchart outlining the steps of this study. Initially, the PLA, PLA-CF, and PLA-GF filaments were analyzed through thermogravimetric analysis (TGA) to validate their fiber content and thermal stability. Optical microscopy was then used to assess fiber dispersion within the polymer matrix. After these characterizations, specimens were fabricated following the specifications of ASTM D3039 for tensile testing, ASTM D7264 for four-point bending tests, and ASTM D5045-99 for the evaluation of fracture parameters, including the critical load (P\u003csub\u003eQ\u003c/sub\u003e), fracture toughness (K\u003csub\u003eIC\u003c/sub\u003e) and strain energy release rate (G\u003csub\u003eIC\u003c/sub\u003e). To further investigate the structural integrity of the printed specimens, porosity analysis was conducted, followed by fracture surface characterization using scanning electron microscopy (SEM) to evaluate fiber-matrix interaction and failure mechanisms. The mechanical behavior of fiber-reinforced FDM composites is examined and discussed in the Results and Discussion section.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003eThe filaments used in this study: PLA, PLA-CF, and PLA-GF are commercially available materials specifically designed for FDM. These filaments were purchased directly from Voolt 3D (Santo Andr\u0026eacute;, Brazil), which provided their nominal composition and fiber specifications. According to the manufacturer, the composite filaments consist of a PLA matrix (80 wt%) reinforced with short carbon or glass fibers (20 wt%), with average fiber lengths of 160 \u0026micro;m and diameters of 13 \u0026micro;m.\u003c/p\u003e\u003cp\u003eFiber contents above 40 wt% can cause percolation effects, leading to extrusion difficulties, nozzle clogging, and weak interlayer adhesion. To maintain processability and enhance mechanical performance, the reinforcement fraction was limited to 20 wt%. Additionally, fiber lengths were controlled near 160 \u0026micro;m, as values around 150 \u0026micro;m optimize reinforcement efficiency and printability.\u003c/p\u003e\u003cp\u003eExcessive fiber loading (above 30\u0026ndash;40 wt%) also increases porosity, reducing stress transfer between fiber and matrix, which weakens tensile and flexural properties. Studies indicate that moderate reinforcement levels (15\u0026ndash;25 wt%) improve mechanical strength without compromising print quality, mitigating the drawbacks of high fiber content [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Process Parameters\u003c/h2\u003e\u003cp\u003eTo determine the appropriate extrusion conditions for each filament, a temperature tower test was performed. This test involved printing a stepped structure at varying temperatures to assess extrusion quality, layer adhesion, and defect formation. Based on these observations, the extrusion temperature was set at 210\u0026deg;C, ensuring proper filament deposition while reducing defects such as warping, under-extrusion, and delamination.\u003c/p\u003e\u003cp\u003eThe printing nozzle diameter was set to 0.4 mm, considering resolution, dimensional accuracy, and filament flow stability. While a 0.8 mm nozzle could help reduce clogging, it often compromises print resolution and layer precision, affecting mechanical property evaluations. The 0.4 mm nozzle ensures consistent filament extrusion and uniform fiber dispersion, which are important for reliable specimen fabrication.\u003c/p\u003e\u003cp\u003eThe printing speed was set at 15 mm/s, since lower speeds promote stronger layer bonding by allowing more time for the material to spread and fuse properly. Printing speeds above 20 mm/s have been reported to increase void formation and delamination, particularly in fiber-reinforced composites, where heat dissipation occurs more rapidly due to the fiber content.\u003c/p\u003e\u003cp\u003eThe layer thickness was fixed at 0.2 mm, a widely used parameter in FDM-printed composites. This setting provides a balance between resolution and mechanical integrity\u0026mdash;thicker layers tend to weaken interlayer adhesion, while thinner layers extend printing time without offering substantial mechanical improvements.\u003c/p\u003e\u003cp\u003eRegarding printing orientation, two raster configurations were selected: 0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg;, as they are commonly used in composite research to assess anisotropic mechanical behavior. The 0\u0026deg;/90\u0026deg; orientation aligns fibers with the principal loading direction, leading to higher tensile strength, while the 45\u0026deg;/-45\u0026deg; orientation introduces shear stresses, improving damage tolerance and energy dissipation. Studies have shown that the combination of axial and shear stress components in 45\u0026deg;/-45\u0026deg; raster patterns enhances impact and fatigue resistance [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Similarly, Spoerk et al. [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e] demonstrated that different raster angles influence interlayer bonding, which directly affects the overall mechanical response of FDM-printed parts.\u003c/p\u003e\u003cp\u003eAlthough a 0\u0026deg; raster orientation generally provides the highest tensile strength, it is often associated with brittle failure and reduced ductility. On the other hand, 45\u0026deg;/-45\u0026deg; orientations promote greater energy absorption and delay catastrophic failure, leading to more durable structures. Previous research highlights that raster angle selection plays a crucial role in flexural and fatigue behavior, reinforcing the necessity of evaluating both 0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg; orientations to obtain a complete understanding of mechanical performance [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe specimens were printed using FDM technology, positioned centrally on the printer platform, and fabricated individually to ensure consistency. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the detailed printing parameters applied in this study. All specimens were printed on the XY plane of the heated bed, ensuring uniformity in material deposition and structural integrity.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePrinting Parameters used for Specimen Fabrication.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eParameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eValues\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eUnits\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrint speed\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e[mm/s]\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInfill density\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInfill patern\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ecubic\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrinting orientation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e[0\u0026deg;/90\u0026ordm;] [45\u0026deg;/-45\u0026deg;]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e[\u0026ordm;]\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLayer height\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e[mm]\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLine width\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e[mm]\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBed temperature\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e[\u0026ordm;C]\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNozzle temperature\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e210\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e[\u0026ordm;C]\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNumber of perimeters\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eWall\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFor slicing the 3D models generated in CAD software (SolidWorks 2008) into individual layers, CURA 5.2 software (Creality Sunlu, China) was used. A dedicated filament dryer (Creality, Sunlu, China) was used to protect the filament spool from moisture absorption, maintaining a temperature of 50\u0026deg;C during the printing process.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Specimens\u003c/h2\u003e\u003cp\u003eFor the tensile test, the specimens were designed according to the dimensions specified by the ASTM D3039 standard, which included a thickness of 4.5 mm, a width of 13 mm, and a length of 165 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). The test was conducted at a speed of 3 mm/min, following the standard procedure to accurately assess the tensile properties of the materials.\u003c/p\u003e\u003cp\u003eFor the four-point bending test, the specimens were designed in accordance with the ASTM D7264 standard. These specifications included a thickness of 10 mm, a height of 20 mm, and a length of 90 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). The test was conducted at a speed of 2 mm/min to evaluate the flexural strength and modulus of the samples. According to the standard, the test was performed until either the specimen fractured or the displacement of the loading punch reached 13 mm, ensuring compliance with the defined failure criteria.\u003c/p\u003e\u003cp\u003eFor the fracture analysis, specimens with a single-edge notch were fabricated following the ASTM D5045-99 standard. The test was conducted in a three-point bending configuration with a constant displacement rate to determine the critical load (P\u003csub\u003eQ\u003c/sub\u003e), the critical strain energy release rate (G\u003csub\u003eIC\u003c/sub\u003e), and the fracture toughness (K\u003csub\u003eIC\u003c/sub\u003e). This evaluation provides insights into the crack initiation and propagation resistance of fiber-reinforced composites.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Testing Equipaments\u003c/h2\u003e\u003cp\u003eTo verify the actual fiber content in the PLA-CF and PLA-GF filaments, thermogravimetric analysis (TGA) was conducted using a TA Instruments Q50 TGA. Samples weighing approximately 10 mg were heated from room temperature to 600\u0026deg;C at a heating rate of 10\u0026deg;C/min under a nitrogen atmosphere to evaluate the thermal degradation profile and residual mass of the PLA, PLA-CF and PLA-GF filaments.\u003c/p\u003e\u003cp\u003eThe void content of the printed specimens was determined using a gravimetric method based\u003c/p\u003e\u003cp\u003eon ASTM D2734. The theoretical density of the material was calculated from its composition, and the actual density was measured using an Analytical Balance Sartorius Entris 224-1S, following standard mass-to-volume ratio procedures. The void content percentage was then computed using Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:V=\\left(1-\\frac{{\\rho\\:}_{measured}}{{\\rho\\:}_{theoretical}}\\right).100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ewhere \u0026#120588;\u003csub\u003e\u0026#119898;\u0026#119890;\u0026#119886;\u0026#119904;\u0026#119906;\u0026#119903;\u0026#119890;\u0026#119889;\u003c/sub\u003e is the experimentally obtained density and \u0026#120588;\u003csub\u003e\u0026#119905;ℎ\u0026#119890;\u0026#119900;\u0026#119903;\u0026#119890;\u0026#119905;\u0026#119894;\u0026#119888;\u0026#119886;\u0026#119897;\u003c/sub\u003e is the theoretical density based on the material's composition.\u003c/p\u003e\u003cp\u003eTensile, four-point bending and fracture toughness tests were conducted using a Shimadzu AG-IS universal testing machine with a 100 kN load capacity. Wedge grips moved at a speed of 3 mm/min for the tensile test and 2 mm/min for the four-point bending test, with data collection (force, grip displacement) at 100 Hz, operating at a temperature of 24\u0026deg;C.\u003c/p\u003e\u003cp\u003eTo investigate the fracture mechanisms and fiber-matrix interaction in the specimens subjected to the tensile test, optical microscopy and scanning electron microscopy (SEM) were performed. Optical micrographs were obtained using a Leica DM750M optical microscope with a high-resolution digital camera. SEM images were acquired to analyze the fracture surfaces after tensile testing, providing insights into fiber pull-out, interfacial adhesion, and failure modes under tensile loading conditions.\u003c/p\u003e\u003cp\u003eThe critical load (P\u003csub\u003eQ\u003c/sub\u003e), the critical strain energy release rate (G\u003csub\u003eIC\u003c/sub\u003e), and the fracture toughness (K\u003csub\u003eIC\u003c/sub\u003e) are key parameters in evaluating the fracture resistance of structures and components under notched conditions, where high stresses concentrate around the notch regions. In this study, these parameters were determined according to the ASTM D5045-99 standard, which is widely applied to polymer-based materials. This standard provides the methodology for calculating these fracture properties, ensuring consistency in material evaluation.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. RESULTS AND DISCUSSION","content":"\u003cp\u003eTo verify the actual fiber content in the PLA-CF and PLA-GF filaments, thermogravimetric analysis (TGA) was conducted. The results confirmed that the fiber reinforcement closely matched the nominal 20 wt% specified by the manufacturer, validating the consistency of the composite formulation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea) and the Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec presents optical micrographs of the reinforced filaments, providing qualitative evidence of fiber dispersion within the polymer matrix.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe thermal degradation behavior of the PLA, PLA-CF, and PLA-GF filaments was analyzed using TGA, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. The onset of weight loss for PLA was observed at approximately 327\u0026deg;C, with the maximum degradation rate occurring around 360\u0026deg;C. The residual mass at 600\u0026deg;C was about 2.5%, indicating minimal inorganic content in the material.\u003c/p\u003e\u003cp\u003eFor PLA-CF, the onset of thermal degradation was detected at around 334\u0026deg;C, with the peak degradation temperature occurring at 371\u0026deg;C. The final residue at 600\u0026deg;C was approximately 23%, suggesting the presence of carbon fiber content, which does not fully decompose under the tested conditions.\u003c/p\u003e\u003cp\u003eSimilarly, the PLA-GF filament exhibited an onset degradation temperature of approximately 323\u0026deg;C, with the maximum degradation rate occurring at 359\u0026deg;C. The residual ash content was significantly higher than that of PLA and PLA-CF, reaching about 21.4% at 600\u0026deg;C. This elevated residue aligns with the expected presence of glass fibers, which remain stable at high temperatures and do not decompose under the conditions of the TGA test.\u003c/p\u003e\u003cp\u003eThe thermogravimetric results confirm the presence of reinforcing fibers in the composite filaments and highlight differences in thermal stability. While carbon fibers provided a slight increase in thermal resistance compared to PLA, the glass fiber-reinforced composite exhibited a significantly higher residual mass due to the non-decomposable nature of the glass content. These findings align with previous studies on fiber-reinforced thermoplastics, demonstrating that fiber type plays a crucial role in the thermal performance of the printed composites.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec presents optical micrographs of the PLA-CF and PLA-GF filaments, showing the dispersion of carbon and glass fibers within the PLA matrix. As indicated by the arrows, the fibers appear well-embedded in the matrix, with their distribution following the extrusion direction. The morphology observed suggests an adequate dispersion of the fibers, which is essential for ensuring consistent mechanical behavior in 3D-printed composites. However, variations in fiber alignment and possible regions of local agglomeration may influence mechanical performance.\u003c/p\u003e\u003cp\u003eHowever, a detailed analysis of the images reveals variations in fiber alignment and orientation, which may directly impact the mechanical properties. In PLA-GF samples, glass fibers tend to maintain a more uniform alignment along the extrusion direction, leading to a more homogeneous reinforcement distribution within the polymeric matrix. This behavior is favorable for load transfer efficiency in the printing direction, which explains the higher stiffness observed in mechanical tests for the 0\u0026deg;/90\u0026deg; orientation [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eConversely, in PLA-CF samples, a more dispersed and partially misaligned fiber distribution is observed, with some fibers exhibiting random inclinations or localized agglomerations. This less uniform distribution may reduce the efficiency of load transfer between matrix and reinforcement, leading to stress concentration zones and a decrease in overall reinforcement efficiency. Additionally, the interaction between the polymeric matrix and fibers differs between carbon and glass reinforcements, affecting interfacial adhesion characteristics and contributing to distinct failure mechanisms during mechanical testing [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe presence of these structural variations aligns with findings from previous studies on FDM-printed fiber-reinforced composites, which highlight that the layer-by-layer deposition and extrusion path significantly influence the final fiber distribution within the polymer matrix. This effect becomes particularly relevant in specimens printed with a -45\u0026deg;/45\u0026deg; orientation, where fiber misalignment may have a more pronounced effect on mechanical strength and deformation response [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e4.1 Tensile Test\u003c/h2\u003e\u003cp\u003eBefore performing the tensile and flexural tests, the void content of the 3D-printed specimens was measured to assess the influence of fiber reinforcement and printing orientation on porosity levels (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). The percentage of voids plays a crucial role in determining the mechanical performance of additively manufactured components, as excessive porosity can compromise interlayer adhesion, reduce stiffness, and introduce stress concentration points that accelerate failure. To evaluate the mechanical performance of the reinforced and unreinforced specimens, tensile tests were conducted to determine Young\u0026rsquo;s modulus (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb), tensile strength (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec), and the maximum force (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) sustained before failure. These properties are critical for assessing how fiber reinforcement and printing orientation influence material stiffness, strength, and structural integrity. The results obtained are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea presents the void content for PLA, PLA-CF, and PLA-GF specimens printed in both 0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg; orientations. The results indicate that PLA exhibited the lowest void content, with values of 6.1% for the 0\u0026deg;/90\u0026deg; orientation and 6.4% for the 45\u0026deg;/-45\u0026deg; orientation. The addition of short fibers significantly increased porosity, with PLA-CF specimens presenting void contents of 8.3% for the 0\u0026deg;/90\u0026deg; orientation and 8.5% for the 45\u0026deg;/-45\u0026deg; orientation. Similarly, PLA-GF specimens displayed void contents of 7.9% and 8.1% for the 0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg; orientations, respectively.\u003c/p\u003e\u003cp\u003eThe results suggest that fiber reinforcement increases the void percentage, which can be attributed to the difficulty in fully compacting the material during deposition. The presence of fibers affects the flow and adhesion of the molten polymer, potentially leading to microstructural discontinuities and interlayer gaps. Furthermore, the printing orientation had a minor influence on porosity levels, with a slight increase in void content for the 45\u0026deg;/-45\u0026deg; orientation across all materials. This trend aligns with findings from the literature, where diagonal raster angles tend to introduce more interlayer gaps due to variations in filament deposition and bonding efficiency.\u003c/p\u003e\u003cp\u003eThe higher porosity levels observed in fiber-reinforced composites highlight the necessity of adjusting printing parameters, such as extrusion temperature, deposition rate, and overlap between adjacent extrusions, to reduce void formation. Controlling these factors is essential for enhancing interfacial adhesion and improving the mechanical performance of 3D-printed composite structures.\u003c/p\u003e\u003cp\u003eThe results for Young\u0026rsquo;s modulus, as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, show clear differences between PLA, PLA-GF, and PLA-CF. For PLA, the values for the 0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg; printing orientations were 2.7 GPa and 2.67 GPa, respectively. By comparison, the PLA-GF specimens exhibited lower values, with 2.17 GPa for the 0\u0026deg;/90\u0026deg; orientation and 2.14 GPa for the 45\u0026deg;/-45\u0026deg; orientation. PLA-CF specimens, however, showed the highest values, with 3.05 GPa for the 0\u0026deg;/90\u0026deg; orientation and 2.59 GPa for the 45\u0026deg;/-45\u0026deg; orientation.\u003c/p\u003e\u003cp\u003eThe higher Young's modulus for PLA-CF compared to both PLA and PLA-GF is expected due to the inherent stiffness of carbon fibers. Carbon fibers are known for their high modulus, which significantly contributes to the overall stiffness of the composite material [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. This explains why PLA-CF exhibited the highest Young\u0026rsquo;s modulus values, particularly in the 0\u0026deg;/90\u0026deg; orientation, where the fibers are aligned with the load direction, thereby enhancing their contribution to the material\u0026rsquo;s stiffness.\u003c/p\u003e\u003cp\u003eFor PLA and PLA-GF, the lower values of Young\u0026rsquo;s modulus can be attributed to the lack of reinforcement in PLA and the lower stiffness of glass fibers in PLA-GF compared to carbon fibers. While glass fibers provide some reinforcement, they are not as rigid as carbon fibers, which explains why the PLA-GF specimens exhibited lower stiffness than PLA-CF [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eInterestingly, the 45\u0026deg;/-45\u0026deg; printing orientation resulted in slightly lower Young\u0026rsquo;s modulus for all materials. This behavior is expected, as the fibers are diagonally oriented relative to the applied tensile load, reducing their ability to resist deformation directly and thereby lowering the modulus. This effect is more pronounced in PLA-CF, where the modulus dropped from 3.05 GPa in the 0\u0026deg;/90\u0026deg; orientation to 2.59 GPa in the 45\u0026deg;/-45\u0026deg; orientation, representing a decrease of approximately 15%. For PLA and PLA-GF, the decreases were much smaller, around 1.1% and 1.4%, respectively, reflecting the lower overall influence of fiber orientation on their mechanical performance.\u003c/p\u003e\u003cp\u003eThe results of tensile strength for different materials and printing orientations demonstrate distinct behaviors. For PLA, the maximum tensile strengths were 47.45 MPa in the 0\u0026deg;/90\u0026deg; orientation and 50.83 MPa in the 45\u0026deg;/-45\u0026deg; orientation. In the case of PLA-GF, the maximum tensile strengths were significantly lower, with values of 28.06 MPa for the 0\u0026deg;/90\u0026deg; orientation and 33.63 MPa for the 45\u0026deg;/-45\u0026deg; orientation. For PLA-CF, the values were 32.97 MPa for the 0\u0026deg;/90\u0026deg; orientation and 41.30 MPa for the 45\u0026deg;/-45\u0026deg; orientation.\u003c/p\u003e\u003cp\u003eThe observation that specimens printed in the 45\u0026deg;/-45\u0026deg; orientation exhibited higher maximum tensile strengths compared to the 0\u0026deg;/90\u0026deg; orientation can be attributed to the more effective distribution of stresses across the printed layers. According to Harshit et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], tensile strength decreases with increasing printing angle. Specimens printed at a 0\u0026deg; angle exhibit layers aligned parallel to the tensile load direction, resulting in higher tensile strength. Conversely, specimens printed at a 45\u0026deg; angle are prone to shear failures, with layers fracturing at approximately 45\u0026deg;. Despite this, they can withstand greater loads compared to specimens printed at a 90\u0026deg; angle, where the load direction is perpendicular to the layer orientation, leading to reduced tensile strength [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn the 45\u0026deg;/-45\u0026deg; orientation, the diagonal arrangement of layers relative to the applied force allows for a more efficient distribution of stresses, thereby increasing resistance to deformation. This orientation may also enhance inter-layer bonding, resulting in superior adhesion and an increased capacity to withstand loads [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe results obtained for the Maximum Forces demonstrate distinct trends among the different materials and printing orientations. PLA specimens exhibited Maximum Forces of 2793.53 N in the 0\u0026deg;/90\u0026deg; orientation and 2944.69 N in the 45\u0026deg;/-45\u0026deg; orientation. These values indicate the superior performance of PLA, likely due to its homogeneity and the absence of reinforcements that could introduce weaknesses within the printed layers, such as porosity and adhesion issues between the PLA matrix and the fibers [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn comparison, the PLA-GF specimens showed Maximum Forces of 1616.03 N in the 0\u0026deg;/90\u0026deg; orientation and 1917.59 N in the 45\u0026deg;/-45\u0026deg; orientation. The reduction in Maximum Forces relative to PLA may be attributed to the characteristics of glass fibers, which, while providing some improvement in strength, are unable to match the structural integrity of PLA. Additionally, the presence of porosity and inferior adhesion between layers could have contributed to the decrease in strength [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe PLA-CF specimens exhibited Maximum Forces of 2087.25 N in the 0\u0026deg;/90\u0026deg; orientation and 2335.22 N in the 45\u0026deg;/-45\u0026deg; orientation. Although PLA-CF demonstrates superior performance compared to PLA-GF, it still falls short of PLA in both orientations. This can be explained by shear failure occurring within the fibers at angled printing orientations, as previously discussed. Furthermore, while the properties of carbon fibers are highly resistant, they may not be sufficient to surpass the mechanical characteristics of PLA, particularly concerning layer adhesion and the presence of porosity that could compromise strength [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents the values of Young's modulus, maximum tensile strength, and maximum force obtained from the tensile test. The stress-strain curves provide valuable insights into the mechanical response of the different materials and printing orientations, showing how reinforcement type and raster angle influence the deformation behavior.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor PLA, the strain values were 0.025 for the 0\u0026deg;/90\u0026deg; orientation and 0.027 for the 45\u0026deg;/-45\u0026deg; orientation. This 8% increase in strain suggests that printed layers deform more easily in the 45\u0026deg;/-45\u0026deg; orientation, where the layer arrangement relative to the applied force allows for greater elongation before failure. The 0\u0026deg;/90\u0026deg; orientation, however, results in a stiffer response, as the extruded layers align with the loading direction, improving resistance to tensile forces.\u003c/p\u003e\u003cp\u003eFor PLA-CF specimens, a reduction in strain was observed compared to PLA. The 0\u0026deg;/90\u0026deg; orientation exhibited a strain of 0.021, representing a 16% decrease relative to PLA. The presence of carbon fibers acts as a reinforcing agent, enhancing stiffness and consequently limiting material elongation. However, in the 45\u0026deg;/-45\u0026deg; orientation, the strain increased to 0.026, approaching the value observed for PLA in the same orientation. This 23.8% increase compared to the 0\u0026deg;/90\u0026deg; orientation suggests that, despite the reinforcing effect of the fibers, layer misalignment allows for greater elongation, similar to what was observed in PLA.\u003c/p\u003e\u003cp\u003eThe stiffest behavior was exhibited by PLA-GF specimens. Regardless of the printing orientation, the strain values remained constant at 0.016, indicating the lowest deformation capacity among all tested samples. The strain reduction was 36% compared to PLA with 0\u0026deg;/90\u0026deg; printing and 23% compared to PLA-CF in the same orientation. This behavior is attributed to the intrinsic rigidity of glass fibers, which effectively deformation. Additionally, the identical strain values between the two orientations suggest that the mechanical response of PLA-GF is dominated by the reinforcement, reducing the influence of raster angle on strain behavior.\u003c/p\u003e\u003cp\u003eDespite the benefits of fiber reinforcement, the adhesion between fibers and the PLA matrix iinfluences mechanical properties. Weak interfacial bonding can lead to premature failure, as inadequate adhesion prevents efficient load transfer from the matrix to the fibers. This phenomenon is particularly relevant in fiber-reinforced composites, where poor adhesion results in pull-out effects and localized stress concentrations.\u003c/p\u003e\u003cp\u003eFurthermore, porosity influences the mechanical behavior of 3D-printed composites. Insufficient bonding between deposited layers and improper fiber wetting can create voids, which act as stress concentrators, promoting crack nucleation and propagation. In a study by Nicolau et al. [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], PLA-GF specimens exhibited reinforcement distribution defects, including fiber agglomeration and matrix porosity, leading to inter and intra-layer delamination. Similar mechanisms could be responsible for the variations in mechanical properties observed in the present study.\u003c/p\u003e\u003cp\u003eIn FDM, adjusting extrusion temperature and deposition time is essential for enhancing inter-layer adhesion and reducing void formation. Rapid heating and cooling cycles can reduce crystallinity and alter the polymer's structural integrity, influencing the final mechanical properties [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Controlling the extrusion process reduces these effects and enhances the performance of fiber-reinforced composites. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e presents the fracture surfaces of the cross-sections of the tested specimens, highlighting the presence of voids and fiber distribution in PLA-GF and PLA-CF composites. These images provide insight into the interlayer adhesion and fracture mechanisms governing the mechanical performance of the materials.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe cross-sectional fracture images (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) reveal notable differences in void distribution and fiber dispersion between PLA-GF and PLA-CF specimens. These characteristics have a direct impact on mechanical performance, as confirmed by the mechanical property data. The presence of voids is more pronounced in PLA-CF specimens compared to PLA-GF, suggesting that fiber-matrix adhesion in PLA-GF is more effective. This behavior may be attributed to a more favorable interaction between the PLA matrix and glass fibers, as well as the processing temperature used during extrusion, which likely improved interlayer bonding and reduced porosity.\u003c/p\u003e\u003cp\u003eIn contrast, PLA-CF specimens exhibit a higher concentration of voids at the interlayer regions. The lower adhesion between carbon fibers and the PLA matrix may have hindered efficient stress transfer, leading to premature failure in tensile loading. This weaker bonding is consistent with the lower mechanical properties observed for PLA-CF when compared to PLA-GF. Additionally, the fracture surfaces of specimens printed at -45\u0026deg;/45\u0026deg; show fewer visible voids in the cross-section. However, this does not necessarily indicate a lower overall porosity in the printed structure. It is well established that this orientation tends to generate more voids due to the deposition pattern, but the fracture may preferentially propagate through regions with better adhesion, leaving void-rich areas less exposed.\u003c/p\u003e\u003cp\u003eThe 0\u0026deg;/90\u0026deg; orientation, on the other hand, appears to exhibit a more consistent interlayer structure. This configuration promotes better stress alignment along the printed layers, leading to higher mechanical resistance and delayed crack propagation. The mechanical data confirm this trend, with PLA-GF showing superior strength and modulus in this orientation compared to PLA-CF. The improved fiber-matrix interaction and reduced void content enhance stress transfer, increasing mechanical performance. Conversely, the higher porosity and weaker fiber-matrix bonding in PLA-CF reduce fracture resistance, leading to earlier failure. Furthermore, the dependence on print orientation is evident, as the 0\u0026deg;/90\u0026deg; orientation results in better load distribution, whereas \u0026minus;\u0026thinsp;45\u0026deg;/45\u0026deg; induces shear stresses that compromise interlayer adhesion.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents the SEM images of the fracture surfaces of PLA-CF and PLA-GF specimens after the tensile test. These images provide provide important insights into the failure mechanisms governing the fiber-reinforced composites, highlighting key aspects such as fiber-matrix adhesion, interfacial debonding, and fiber pull-out.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor PLA-CF specimens (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea), the failure mode is primarily characterized by fiber-matrix debonding, evidenced by the widening of the fiber-matrix interface (debonding zone) before complete fiber extraction. This phenomenon occurs due to insufficient adhesion between the carbon fibers and the PLA matrix, leading to ineffective stress transfer. As a result, under tensile loading, the fibers detach from the matrix rather than breaking, leaving pull-out cavities in the fracture surface. This behavior is consistent with findings reported by Zhang et al. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], who observed that weak interfacial bonding in carbon fiber-reinforced composites limits load transfer efficiency, thus reducing tensile strength.\u003c/p\u003e\u003cp\u003eConversely, for PLA-GF specimens (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb), the observed fracture surfaces exhibit fiber pull-out with cleaner fiber-matrix interfaces, suggesting a relatively stronger adhesion compared to PLA-CF. The presence of smaller debonding zones indicates a better stress distribution across the interface, which enhances mechanical performance. Studies by Li et al. [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e] and Bian et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] have shown that glass fibers typically establish better interfacial bonding with polymer matrices due to enhanced chemical compatibility, resulting in reduced fiber extraction and improved stress transfer. This difference in adhesion can explain the higher flexural strength of PLA-GF observed in the bending tests.\u003c/p\u003e\u003cp\u003eAdditionally, voids were identified in both composites, likely resulting from the detachment of fibers during tensile loading or incomplete impregnation during filament fabrication. These voids act as stress concentrators, further compromising mechanical properties. T\u0026uuml;rk et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] emphasize that porosity and weak fiber-matrix interfaces are two primary factors that govern failure mechanisms in short-fiber-reinforced composites manufactured by FDM.\u003c/p\u003e\u003cp\u003eThe comparison between PLA-CF and PLA-GF reinforces the critical role of interfacial adhesion in dictating the mechanical response of fiber-reinforced composites. The more pronounced debonding effect in PLA-CF suggests a lower interfacial shear strength between the carbon fibers and PLA, whereas PLA-GF benefits from stronger fiber-matrix interactions. This observation aligns with previous studies on fiber-reinforced 3D-printed composites, which indicate that stronger interfacial bonding improves mechanical performance [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe fiber pull-out observed in PLA-CF, combined with extensive debonding regions, indicates limited stress transfer capability, leading to premature failure. Meanwhile, PLA-GF exhibits a more effective load transfer mechanism, reducing the likelihood of fiber detachment and enhancing mechanical integrity.\u003c/p\u003e\u003cp\u003eTo validate the statistical significance of the differences observed in mechanical performance, an analysis of variance (ANOVA) was conducted. This statistical approach was employed to assess the impact of reinforcement type and printing orientation on Young\u0026rsquo;s modulus, tensile strength, and maximum force. The ANOVA results, presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, provide insights into the relative contributions of these factors to the overall mechanical behavior of the specimens. A confidence level of 95% was applied, corresponding to a P-value threshold of 0.05, ensuring that only statistically significant differences were considered.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eANOVA Results \u0026ndash; Tensile Test\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSource of variation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eYoung's Modulus\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003eTensile Strength\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003eMaximum Force\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eF-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eF-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eF-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType of reinforcement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e233.32\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1568.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e21641\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrinting orientation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e45.88\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e240.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e35274\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType of reinforcement*Printing orientation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e43.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e9.27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.001\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e1567.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e96.15%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e98.30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e98.99%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBold values indicate p\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe ANOVA results confirm that both the type of reinforcement and printing orientation have a statistically significant effect on the mechanical properties, as indicated by the low P-values (\u0026lt;\u0026thinsp;0.05) and high F-values. The interaction between reinforcement type and printing orientation was also significant, particularly for Young\u0026rsquo;s modulus (F\u0026thinsp;=\u0026thinsp;43.13, P\u0026thinsp;=\u0026thinsp;0.000) and maximum force (F\u0026thinsp;=\u0026thinsp;1567.7, P\u0026thinsp;=\u0026thinsp;0.000). This suggests that the impact of orientation is highly dependent on the type of reinforcement used.\u003c/p\u003e\u003cp\u003eNotably, the R\u0026sup2; values indicate that the model explains nearly all the variability in the data, particularly for tensile strength (98.30%) and maximum force (98.99%). These high values demonstrate that reinforcement type and printing orientation are the primary determinants of mechanical behavior in FDM-printed composites.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e4.2 Four Bending Test\u003c/h2\u003e\u003cp\u003eBefore the four-point bending tests, the void percentage of the printed specimens was evaluated. The results obtained were similar to those observed for the specimens intended for the tensile tests, with a variation of only 1.3%. The results of the four-point bending test are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The analysis focuses on the influence of fiber reinforcement and print orientation on the flexural properties of the specimens. The primary mechanical parameters evaluated include Flexural Modulus, Maximum Force, and Flexural Strength, providing insights into the stiffness and load-bearing capacity of the composites under bending loads. Following the ASTM D7264 standard, the tests were interrupted when the punch displacement reached 13 mm. In all specimens, no complete fracture was observed during testing, indicating that the materials exhibited high deformation capacity under bending conditions.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe Flexural Modulus values obtained from the four-point bending test provide relevant information about the stiffness of the materials under flexural loads. For PLA, the Flexural Modulus was 0.98 GPa in the 0\u0026ordm;/90\u0026deg; orientation and 1.04 GPa in the 45\u0026ordm;/-45\u0026deg; orientation, showing a 6.12% increase for the 45\u0026ordm;/-45\u0026deg; specimens. This small variation can be attributed to a more uniform stress distribution during bending in the 45\u0026ordm;/-45\u0026deg; orientation, which slightly increases stiffness. However, the difference between the two orientations is relatively small, indicating that for PLA, print orientation has little effect on its flexural behavior [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn the case of PLA-GF, the Flexural Modulus was 1.15 GPa for the 0\u0026ordm;/90\u0026deg; orientation and 1.01 GPa for the 45\u0026ordm;/-45\u0026deg; orientation. Here, the 0\u0026ordm;/90\u0026deg; orientation exhibits a higher Flexural Modulus, with an approximately 13.9% increase compared to the 45\u0026ordm;/-45\u0026deg; orientation. This difference can be explained by the alignment of the glass fibers in the 0\u0026ordm;/90\u0026deg; direction, which is more effective in bearing loads parallel to the fiber direction. Glass fibers, being relatively stiff, enhance the modulus when aligned with the load direction, which explains the higher values observed in the 0\u0026ordm;/90\u0026deg; specimens. The 45\u0026ordm;/-45\u0026deg; orientation introduces shear forces between fibers and matrix, resulting in a lower Flexural Modulus [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA-CF, the Flexural Modulus was 1.13 GPa in the 0\u0026ordm;/90\u0026deg; orientation and 1.08 GPa in the 45\u0026ordm;/-45\u0026deg; orientation, with a 4.42% decrease for the 45\u0026ordm;/-45\u0026deg; orientation. The smaller difference between the two orientations compared to the PLA-GF I suggests that carbon fibers contribute to maintaining stiffness even when subjected to multi-directional loads. This behavior is likely related to their load transfer characteristics of carbon fibers, which help retain a relatively high modulus even when the printing orientation introduces shear components [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe overall comparison of the materials highlights that both PLA-GF and PLA-CF demonstrate higher Flexural Modulus values than PLA, as expected due to the reinforcing effect of the fibers. However, the print orientation affects these materials differently. In PLA-GF, the modulus decreases in the 45\u0026ordm;/-45\u0026deg; orientation, while PLA-CF shows a more consistent performance across both orientations. This behavior can be attributed to the superior mechanical properties and bonding behavior of carbon fibers compared to glass fibers, allowing for better stress distribution even in non-parallel orientations [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA, the Maximum Force in the 0\u0026ordm;/90\u0026deg; orientation was 975.46 N, while for the 45\u0026ordm;/-45\u0026deg; orientation it was 882.57 N. This represents a 9.5% decrease in Maximum Force for the 45\u0026ordm;/-45\u0026deg; specimens. The difference in Maximum Force between the two orientations can be attributed to the alignment of the layers relative to the applied load. In the 0\u0026ordm;/90\u0026deg; orientation, the layers are better positioned to bear the applied stress, resulting in greater resistance to bending. In contrast, the 45\u0026ordm;/-45\u0026deg; orientation, shear forces develop between the layers, weakening the structure and leading to earlier failure under bending loads [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn the case of PLA-GF, the Maximum Force was 1186.66 N in the 0\u0026ordm;/90\u0026deg; orientation and 913.72 N in the 45\u0026ordm;/-45\u0026deg; orientation, representing a 23% decrease in Maximum Force for the 45\u0026ordm;/-45\u0026deg; orientation. This reduction can be explained by the fact that glass fibers are highly effective at reinforcing the material when aligned with the direction of the applied load, as in the 0\u0026ordm;/90\u0026deg; orientation. In this orientation, the fibers are better positioned to support the bending forces, providing enhanced strength. In the 45\u0026ordm;/-45\u0026deg; orientation, however, the load is applied at an angle to the fibers, reducing their ability to resist bending and leading to a lower Maximum Force [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA-CF, the Maximum Force was 1000.84 N in the 0\u0026ordm;/90\u0026deg; orientation and 906.06 N in the 45\u0026ordm;/-45\u0026deg; orientation, resulting in a 9.4% decrease in the 45\u0026ordm;/-45\u0026deg; orientation. The smaller difference in Maximum Force between the two orientations compared to PLA-GF suggests that carbon fibers are more capable of handling loads even when the layers are printed at an angle. This can be attributed to the superior load transfer properties of carbon fibers, which provide good reinforcement even in the 45\u0026ordm;/-45\u0026deg; orientation. Nevertheless, the 0\u0026ordm;/90\u0026deg; orientation still offers better performance, as the fibers are aligned to directly counteract the applied forces, providing greater resistance to bending [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA, the flexural strength in the 0\u0026ordm;/90\u0026deg; orientation was 14.32 MPa, while in the 45\u0026ordm;/-45\u0026deg; orientation, it dropped to 13.23 MPa. This represents a 7.6% decrease in flexural strength when shifting from the 0\u0026ordm;/90\u0026deg; to the 45\u0026ordm;/-45\u0026deg; orientation. The alignment of the layers in the 0\u0026ordm;/90\u0026deg; orientation allows the material to better withstand bending stresses, as the layers are oriented to carry the load effectively. Conversely, in the 45\u0026ordm;/-45\u0026deg; orientation, shear forces come into play, reducing the effective strength of the material [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA-GF, the flexural strength was 17.79 MPa in the 0\u0026ordm;/90\u0026deg; orientation and decreased to 13.70 MPa in the 45\u0026ordm;/-45\u0026deg; orientation, representing a 23% decrease. This reduction highlights the role of fiber alignment in load resistance. Glass fibers provide effective reinforcement when aligned with the load, enhancing composite\u0026rsquo;s strength. In the 45\u0026ordm;/-45\u0026deg; orientation, the fibers are less aligned with the load, reducing their contribution to flexural strength [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA-CF, the flexural strength for the 0\u0026ordm;/90\u0026deg; orientation was 15.01 MPa, while for the 45\u0026ordm;/-45\u0026deg; orientation, it decreased to 13.58 MPa. The smaller reduction in strength compared to PLA-GF suggests that carbon fibers still contribute to load transfer, even when their orientation does not fully align with the applied force [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe stress-strain curves obtained from the four-point bending tests describe the mechanical response of the materials under flexural loading. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows the average stress-strain behavior of PLA, PLA-GF, and PLA-CF specimens in both 0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg; print orientations. These curves enable a comparative analysis of stiffness and yield behavior, showing the influence of fiber reinforcement and print direction on flexural performance. While these results provide an overall assessment of the materials\u0026rsquo; mechanical response under bending loads, the ultimate failure mechanisms require additional fractographic analysis to be properly identified.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFor PLA, the strain measured at failure in the 0\u0026deg;/90\u0026deg; orientation was 0.046 mm/mm, while in the 45\u0026deg;/-45\u0026deg; orientation, it slightly decreased to 0.045 mm/mm. This small variation of approximately 2.17% suggests that printing orientation has a little influence on the flexural deformation of PLA, likely due to the lack of fiber reinforcement. Since the mechanical properties depend on the polymer matrix, the difference can be attributed to slight variations in stress distribution between the two orientations [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA-GF, the strain values were 0.045 mm/mm for the 0\u0026deg;/90\u0026deg; orientation and 0.047 mm/mm for the 45\u0026deg;/-45\u0026deg; orientation, corresponding to a 4.26% increase in the 45\u0026deg;/-45\u0026deg; orientation. This trend can be explained by the orientation-dependent load transfer capacity of the glass fibers. In the 0\u0026deg;/90\u0026deg; orientation, the fibers are better aligned to bear the applied loads, leading to a stiffer response. In contrast, in the 45\u0026deg;/-45\u0026deg; orientation, the load is distributed along multiple directions, increasing the influence of the polymer matrix, which allows for slightly greater deformation before failure [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eFor PLA-CF, the strain at failure was 0.044 mm/mm in the 0\u0026deg;/90\u0026deg; orientation and 0.046 mm/mm in the 45\u0026deg;/-45\u0026deg; orientation, showing a 4.55% increase in strain for the latter configuration. The increase in strain in the 45\u0026deg;/-45\u0026deg; orientation can be attributed to the anisotropic nature of carbon fibers, which provide the highest stiffness when aligned with the loading direction. In the 0\u0026deg;/90\u0026deg; orientation, the fibers resist bending more effectively, reducing strain. However, in the 45\u0026deg;/-45\u0026deg; orientation, their contribution is reduced, allowing for greater deformation before failure [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eComparing the materials, PLA exhibited the highest strain values, followed by PLA-CF and PLA-GF. The lower deformation observed in PLA-GF specimens suggests that glass fibers restrict deformation more effectively than carbon fibers. This behavior is consistent with findings in the literature that emphasize the higher intrinsic stiffness of glass fibers compared to carbon fibers under flexural loads [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTo statistically validate the effects of fiber reinforcement and printing orientation on the bending properties of the tested specimens, ANOVA was performed. The objective of this analysis is to determine whether the observed variations in Flexural Modulus, Flexural Strength, and Maximum Force are statistically significant or if they could be attributed to experimental variability. By applying ANOVA, it is possible to assess the individual contribution of each factor, as well as the interaction effects between fiber reinforcement and printing orientation, ensuring a comprehensive evaluation of the mechanical behavior of the composites. The results of the ANOVA are presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eANOVA Results \u0026ndash; Four Bending Test\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"10\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSource of variation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eFlexural Modulus\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eFlexural Strength\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003eMaximum Force\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eF-value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eF-value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eF-value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType of reinforcement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1665.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e272.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e78.66\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrint orientation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e264.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e202.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e115.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType of reinforcement*Print orientation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e72.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e155.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e42.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e99.36%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e97.78%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e93.71%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBold values indicate p\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe interaction effect between reinforcement type and printing orientation is particularly significant for Flexural Strength (F\u0026thinsp;=\u0026thinsp;155.09) and Maximum Force (F\u0026thinsp;=\u0026thinsp;42.3), indicating that the mechanical response of the material is not solely dependent on the individual factors, but also on how these parameters interact. This suggests that adjusting both fiber alignment and printing strategy is essential for enhancing mechanical performance. Additionally, the high R\u0026sup2; values, such as 99.36% for Flexural Modulus and 97.78% for Flexural Strength, confirm that these variables account for most of the observed variance, emphasizing their importance in determining the mechanical properties of the material.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e4.3 \u003cb\u003eFracture Toughness Test\u003c/b\u003e\u003c/h2\u003e\u003cp\u003eThe analysis of fracture resistance in FDM-printed composites requires the evaluation of key parameters that influence crack initiation and propagation. The critical load (P\u003csub\u003eQ\u003c/sub\u003e), the critical strain energy release rate (G\u003csub\u003eIC\u003c/sub\u003e), and the fracture toughness (K\u003csub\u003eIC\u003c/sub\u003e) provide a comprehensive understanding of the material's ability to resist mechanical failure. These parameters are essential for assessing the effect of fiber reinforcement and print orientation on fracture behavior. The values of P\u003csub\u003eQ\u003c/sub\u003e, G\u003csub\u003eIC\u003c/sub\u003e, and K\u003csub\u003eIC\u003c/sub\u003e were determined based on ASTM D5045-99, and the results are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea, \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb, and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe P\u003csub\u003eQ\u003c/sub\u003e results complement the G\u003csub\u003eIC\u003c/sub\u003e and K\u003csub\u003eIC\u003c/sub\u003e findings, demonstrating the influence of fiber reinforcement and printing orientation on fracture resistance. Specimens printed in the 0\u0026deg;/90\u0026deg; orientation exhibited higher P\u003csub\u003eQ\u003c/sub\u003e values than those in the 45\u0026deg;/-45\u0026deg; orientation, confirming the role of layer alignment in fracture resistance. The 0\u0026deg;/90\u0026deg; configuration improves load transfer and stress redistribution, delaying crack propagation. In contrast, the 45\u0026deg;/-45\u0026deg; orientation induces higher interlaminar shear stresses, reducing fracture resistance.\u003c/p\u003e\u003cp\u003eFor PLA, the P\u003csub\u003eQ\u003c/sub\u003e values were 1223.63 N for 0\u0026deg;/90\u0026deg; and 862.52 N for 45\u0026deg;/-45\u0026deg;, 29.5% decrease. This suggests that layer bonding in the 0\u0026deg;/90\u0026deg; orientation better resists fracture. Since PLA no fiber reinforcement, its fracture behavior depends mainly on interlayer adhesion, which is more susceptible to stress concentration when loaded at oblique angles.\u003c/p\u003e\u003cp\u003eFor PLA-GF, the P\u003csub\u003eQ\u003c/sub\u003e values were 1186.66 N for 0\u0026deg;/90\u0026deg; and 930.12 N for 45\u0026deg;/-45\u0026deg;, showing a 21.6% reduction. This difference highlights the importance of fiber orientation in improving load-bearing capacity. When glass fibers are aligned with the principal loading direction, they act as effective barriers to crack propagation. However, in the 45\u0026deg;/-45\u0026deg; orientation, the misalignment of fibers leads to reduced energy dissipation and lower fracture resistance, reinforcing observations previously reported for fiber-reinforced polymer composites.\u003c/p\u003e\u003cp\u003eFor PLA-CF, the P\u003csub\u003eQ\u003c/sub\u003e values were 1002.83 N for 0\u0026deg;/90\u0026deg; and 897.66 N for 45\u0026deg;/-45\u0026deg;, reflecting a 10.5% decrease. The smaller difference suggests that carbon fibers provide some degree of fracture resistance even when fiber alignment is less favorable. The higher stiffness of carbon fibers may contribute to stress redistribution, reducing localized stress concentrations and delaying crack propagation.\u003c/p\u003e\u003cp\u003eThe G\u003csub\u003eIC\u003c/sub\u003e values, which represent the material\u0026rsquo;s energy absorption capacity before crack propagation, followed the same trend. The 0\u0026deg;/90\u0026deg; orientation consistently showed higher GIC values than the 45\u0026deg;/-45\u0026deg; orientation, confirming that fiber alignment improves stress transfer and delays crack initiation.\u003c/p\u003e\u003cp\u003eFor PLA, the G\u003csub\u003eIC\u003c/sub\u003e was 10.31 kJ/m\u0026sup2; in the 0\u0026deg;/90\u0026deg; orientation and 4.70 kJ/m\u0026sup2; in the 45\u0026deg;/-45\u0026deg; orientation, a 54.4% reduction. The lower GIC in the 45\u0026deg;/-45\u0026deg; orientation suggests that cracks propagate more easily due to weaker interlayer adhesion and higher shear stresses at misaligned layer interfaces.\u003c/p\u003e\u003cp\u003eFor PLA-GF, the G\u003csub\u003eIC\u003c/sub\u003e was 7.98 kJ/m\u0026sup2; for the 0\u0026deg;/90\u0026deg; orientation, decreasing to 5.64 kJ/m\u0026sup2; in the 45\u0026deg;/-45\u0026deg; orientation, a 29.3% reduction. This reduction highlights the role of fiber alignment in energy dissipation. When glass fibers are aligned with the loading direction, they act as crack barriers, requiring more energy for fracture initiation. In the 45\u0026deg;/-45\u0026deg; orientation, fiber misalignment reduces their reinforcing effect, leading to lower energy absorption.\u003c/p\u003e\u003cp\u003eFor PLA-CF, the G\u003csub\u003eIC\u003c/sub\u003e values were 5.84 kJ/m\u0026sup2; in the 0\u0026deg;/90\u0026deg; orientation and 4.88 kJ/m\u0026sup2; in the 45\u0026deg;/-45\u0026deg; orientation, a 16.4% reduction. Compared to PLA-GF, this smaller decrease suggests that carbon fibers contribute to fracture resistance even when fiber alignment is not ideal. The higher stiffness of carbon fibers may facilitate stress redistribution, reducing localized stress concentrations and slowing crack propagation.\u003c/p\u003e\u003cp\u003eThe K\u003csub\u003eIC\u003c/sub\u003e values, which represent fracture toughness, followed the same trend, with higher values in the 0\u0026deg;/90\u0026deg; orientation across all materials. This behavior is attributed to layer and fiber alignment with the loading direction, improving stress transfer and reducing stress concentrations at interlayer regions.\u003c/p\u003e\u003cp\u003eFor PLA, the K\u003csub\u003eIC\u003c/sub\u003e was 3.13 MPa\u0026middot;m\u0026sup1;/\u0026sup2; in the 0\u0026deg;/90\u0026deg; orientation and 2.20 MPa\u0026middot;m\u0026sup1;/\u0026sup2; in the 45\u0026deg;/-45\u0026deg; orientation, a 29.5% reduction. This suggests that interlayer adhesion is more effective in the 0\u0026deg;/90\u0026deg; orientation, improving stress redistribution and fracture resistance.\u003c/p\u003e\u003cp\u003eFor PLA-GF, the K\u003csub\u003eIC\u003c/sub\u003e was 3.03 MPa\u0026middot;m\u0026sup1;/\u0026sup2; in the 0\u0026deg;/90\u0026deg; orientation and 2.37 MPa\u0026middot;m\u0026sup1;/\u0026sup2; in the 45\u0026deg;/-45\u0026deg; orientation, a 21.6% reduction. This result reinforces the role of fiber alignment in distributing applied stresses, as glass fibers oriented with the principal stress direction improve fracture resistance. Misaligned fibers in the 45\u0026deg;/-45\u0026deg; orientation reduce the material\u0026rsquo;s ability to withstand crack propagation.\u003c/p\u003e\u003cp\u003eFor PLA-CF, the K\u003csub\u003eIC\u003c/sub\u003e was 2.56 MPa\u0026middot;m\u0026sup1;/\u0026sup2; in the 0\u0026deg;/90\u0026deg; orientation and 2.29 MPa\u0026middot;m\u0026sup1;/\u0026sup2; in the 45\u0026deg;/-45\u0026deg; orientation, a 10.5% decrease. Compared to PLA-GF, this smaller difference suggests that carbon fibers enhance fracture resistance even in less favorable alignments. However, their weaker interfacial adhesion with the PLA matrix may explain the lower K\u003csub\u003eIC\u003c/sub\u003e values compared to PLA-GF.\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the results of the ANOVA for P\u003csub\u003eQ\u003c/sub\u003e, G\u003csub\u003eIC\u003c/sub\u003e, K\u003csub\u003eIC\u003c/sub\u003e, obtained from the fracture toughness test. The analysis revealed P-values lower than 0.05, indicating statistically significant differences in fracture toughness values among the tested materials and printing orientations.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eANOVA results for critical load (PQ), critical strain energy release rate (GIC), and fracture toughness (KIC) from fracture toughness tests - PLA, PLA-CF, and PLA-GF\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"10\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSource of variation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eP\u003csub\u003eQ\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eG\u003csub\u003eIC\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u003cp\u003eK\u003csub\u003eIC\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eF-value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eF-value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eF-value\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eP-Value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType of reinforcement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e214.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e237.03\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.020\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e260.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrint orientation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e838.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e885\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e754.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eType of reinforcement*Print orientation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e57.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e60.47\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e109.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e0.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e94.05%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e97.78%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e98.42%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBold values indicate p\u0026thinsp;\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe ANOVA results confirm that both reinforcement type and printing orientation influence fracture resistance across all analyzed parameters (P\u003csub\u003eQ\u003c/sub\u003e, G\u003csub\u003eIC\u003c/sub\u003e, and K\u003csub\u003eIC\u003c/sub\u003e). Printing orientation had the greatest effect, as indicated by high F-values (F\u003csub\u003ePQ\u003c/sub\u003e=838.9, F\u003csub\u003eGIC\u003c/sub\u003e=885.0, F\u003csub\u003eKIC\u003c/sub\u003e=754.97, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), reinforcing the role of layer alignment and fiber orientation in fracture behavior. Crack propagation resistance depends on how stress is distributed along the printed layers, a well-documented phenomenon in anisotropic materials.\u003c/p\u003e\u003cp\u003eReinforcement type also played a statistically significant role (F\u003csub\u003ePQ\u003c/sub\u003e =214.54, F\u003csub\u003eGIC\u003c/sub\u003e =237.03, F\u003csub\u003eKIC\u003c/sub\u003e =260.8, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), confirming that fiber inclusion directly affects the mechanical performance of PLA composites. Among the tested materials, PLA-GF exhibited the highest fracture toughness (K\u003csub\u003eIC\u003c/sub\u003e) and strain energy release rate (G\u003csub\u003eIC\u003c/sub\u003e), highlighting the beneficial effect of glass fibers in improving crack resistance through enhanced fiber-matrix load transfer. PLA-CF, however, showed more consistent performance across orientations, suggesting that carbon fibers contribute to fracture resistance even in less favorable layer alignments.\u003c/p\u003e\u003cp\u003eThe interaction between reinforcement type and printing orientation was also significant (F\u003csub\u003ePQ\u003c/sub\u003e =57.77, F\u003csub\u003eGIC\u003c/sub\u003e =60.47, F\u003csub\u003eKIC\u003c/sub\u003e =109.8, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), indicating that these factors influence each other in determining fracture behavior. This interaction was particularly strong for GIC, where printing orientation had the most pronounced effect. The high R\u0026sup2; values (R\u0026sup2;\u003csub\u003ePQ\u003c/sub\u003e=94.05%, R\u0026sup2;\u003csub\u003eGIC\u003c/sub\u003e =97.78%, R\u0026sup2;\u003csub\u003eKIC\u003c/sub\u003e =98.42%) confirm that the tested factors explain nearly all observed variations in fracture resistance. These results align with previous studies, such as Zhang et al. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], who reported that fiber-reinforced composites exhibit enhanced fracture resistance when fibers are aligned with the principal stress direction. Similarly, Rajpurohit et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] found that anisotropic behavior induced by layer orientation strongly affects fracture performance.\u003c/p\u003e\u003cp\u003eThe superior K\u003csub\u003eIC\u003c/sub\u003e and G\u003csub\u003eIC\u003c/sub\u003e values observed in the 0\u0026deg;/90\u0026deg; orientation across all materials indicate that stress redistribution is more efficient when fibers and layers align with the applied force, improving fracture toughness. PLA-GF exhibited higher K\u003csub\u003eIC\u003c/sub\u003e and G\u003csub\u003eIC\u003c/sub\u003e than PLA-CF in this orientation, likely due to stronger interfacial bonding between glass fibers and the PLA matrix. Conversely, despite their high stiffness, carbon fibers may have weaker adhesion with the polymer matrix, potentially reducing crack resistance in certain orientations.\u003c/p\u003e\u003cp\u003eThe fracture analysis provides further insights into the failure mechanisms of PLA composites reinforced with carbon and glass fibers. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e illustrates the fracture behavior of PLA-CF and PLA-GF specimens in both 0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg; orientations.\u003c/p\u003e\u003cp\u003eFor PLA-CF specimens, fracture initiation occurred at the inner and outer radii of the notch curvature (Figs.\u0026nbsp;\u0026lt;link rid=\"fig11\"\u0026gt;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u0026lt;/link\u0026gt;\u003c/span\u003ea and \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e), with the most pronounced fracture zone at the inner radius, where stress levels were highest due to the bending moment. Microscopic analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ec) shows carbon fibers aligned with the tensile stress direction, suggesting a stress-induced fracture mechanism. This observation supports the findings of Rajpurohit et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], who reported that stronger interlayer adhesion in the 0\u0026deg;/90\u0026deg; orientation contributes to higher flexural strength.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn contrast, PLA-GF specimens exhibited a different fracture pattern (Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ed and \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ee). Fracture initiation was observed at the point of maximum force application, with crack propagation occurring more uniformly along the interlayer regions. The concentration of tensile stresses near the fracture region suggests better interlayer bonding in PLA-GF compared to PLA-CF. Microscopic analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ef) further supports this observation, showing fractured glass fibers aligned with the applied load, indicating more effective load transfer. The stronger fiber-matrix interface in PLA-GF likely enhances crack bridging, contributing to improved fracture toughness.\u003c/p\u003e\u003cp\u003eAdditionally, specimens printed in the 0\u0026deg;/90\u0026deg; orientation consistently exhibited higher fracture resistance than those printed in 45\u0026deg;/-45\u0026deg;. This trend aligns with studies demonstrating that layer alignment parallel to the bending plane enhances resistance to flexural loads [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Failure initiation typically occurred on the tensile side of the specimen, but compressive forces counteracted crack propagation, preserving layer cohesion and improving overall structural integrity.\u003c/p\u003e\u003cp\u003eThese results reinforce the role of fiber alignment, interlayer adhesion, and fiber-matrix load transfer in governing the fracture resistance of FDM-printed composites, highlighting the importance of printing orientation and reinforcement selection in enhancing mechanical performance under bending conditions.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study analyzed the influence of short carbon and glass fiber reinforcement, as well as print orientation, on the mechanical properties, fracture behavior, and thermal stability of FDM-printed PLA composites. The results indicate that both fiber type and raster orientation significantly affect the structural integrity of the printed specimens.\u003c/p\u003e\u003cp\u003eTensile tests demonstrated that PLA specimens printed in the 45\u0026deg;/-45\u0026deg; orientation exhibited the highest tensile strength, reaching 50.83 MPa. This behavior suggests that diagonal raster orientations enhance load distribution, reducing stress concentration under uniaxial loading. In contrast, flexural tests revealed that PLA-GF specimens with a 0\u0026deg;/90\u0026deg; print orientation achieved the highest flexural strength (17.79 MPa), representing a 24.23% increase compared to pure PLA. The alignment of glass fibers with the primary stress direction contributed to enhanced load transfer efficiency and flexural resistance.\u003c/p\u003e\u003cp\u003eThe fracture toughness analysis showed that the 0\u0026deg;/90\u0026deg; orientation resulted in higher K\u003csub\u003eIC\u003c/sub\u003e values across all materials, reinforcing the role of fiber and layer alignment in crack propagation resistance. The higher fracture toughness of PLA-GF compared to PLA-CF suggests that glass fibers promote stronger interfacial adhesion, leading to improved energy dissipation during fracture. Fractographic analysis confirmed that fiber pull-out and interfacial debonding were the predominant failure mechanisms in fiber-reinforced composites, demonstrating the critical influence of fiber-matrix interaction on the mechanical response.\u003c/p\u003e\u003cp\u003ePorosity analysis revealed that fiber-reinforced composites exhibited higher void content, which negatively affected both tensile and flexural performance. This finding highlights the importance of adjusting printing parameters, such as extrusion temperature and raster orientation, to reduce void formation and enhance interlayer bonding. TGA confirmed that PLA-CF exhibited higher thermal stability than PLA-GF, suggesting that carbon fiber reinforcement improves the resistance of PLA composites to thermal degradation. Additionally, the fiber content obtained through TGA closely matched the manufacturer\u0026rsquo;s nominal values, confirming the uniform dispersion of fibers within the polymer matrix.\u003c/p\u003e\u003cp\u003eThe results demonstrated that both fiber reinforcement and printing orientation significantly influence the mechanical and fracture behavior of FDM-printed PLA composites. The 0\u0026deg;/90\u0026deg; orientation consistently resulted in higher P\u003csub\u003eQ\u003c/sub\u003e, K\u003csub\u003eIC\u003c/sub\u003e and G\u003csub\u003eIC\u003c/sub\u003e values, indicating superior fracture resistance due to enhanced stress redistribution and fiber-matrix load transfer. Among the tested materials, PLA-GF exhibited the highest K\u003csub\u003eIC\u003c/sub\u003e 3.03 MPa\u0026middot;m\u0026sup1;/\u0026sup2; and G\u003csub\u003eIC\u003c/sub\u003e 7.98 kJ/m\u0026sup2;), while PLA-CF showed the lowest reduction in fracture resistance between orientations, suggesting a more stable performance under different loading conditions.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank the Postgraduate Program in mechanical Engineering of the Federal University of Minas Gerais (UFMG), Brazil, for the provision of laboratory facilities.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis work was partly financed by the Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior (CAPES)\u0026ndash;Finance Code 001. Also, it must be acknowledged the financial support of the Conselho Nacional de Desenvolvimento Cient\u0026iacute;fico e Tecnol\u0026oacute;gico (CNPq) and Funda\u0026ccedil;\u0026atilde;o de Amparo \u0026agrave; Pesquisa do Estado de Minas Gerais (FAPEMIG).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors confirm that the data supporting the findings of this study are available within the article.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll authors have previously approved this paper and judged that there is no ethical infringement. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to participate and publication\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll authors would like to declare that they have approved their participation and consent about the publication in this journal. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFrederico de Castro Magalhaes: conceptualization, data curation, formal analysis, investigation, methodology, review and editing, validation. Pilar Fabra Rivera: conceptualization, data curation, formal analysis, investigation, methodology, writing \u0026mdash; original draft, writing-review and editing. Juan Campos Rubio: data curation, conceptualization, methodology, resources, supervision, writing-review and editing. All authors have read and agreed to the published version of the manuscript.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eRarani, M., Afarani, R., Zahedi, A.M. (2019). Mechanical characterization of FDM 3D printing of continuous carbon fiber reinforced PLA composites. Composites Part B: Engineering, 175, 107147. https://doi.org/https://doi.org/10.1016/j.compositesb.2019.107147 \u003c/li\u003e\n\u003cli\u003eVallejo J, Garc\u0026iacute;a-Plaza E, N\u0026uacute;\u0026ntilde;ez P.J, Chac\u0026oacute;n J.M, Caminero M.A, Romero A. (2023). 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Advances in Manufacturing, 6, 430-441. https://doi.org/https://doi.org/10.1007/s40436-018-0237-6\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Additive manufacturing, FDM, short fibers, PLA, fiber-reinforced polymer composites","lastPublishedDoi":"10.21203/rs.3.rs-7336068/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7336068/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFused Deposition Modeling (FDM) is a widely used additive manufacturing technique due to its efficiency in producing complex structures at low cost with minimal material waste. However, weak interlayer adhesion and void formation limit the mechanical performance of printed components. This study evaluates the effect of short fiber reinforcement (carbon and glass) and printing orientation (0\u0026deg;/90\u0026deg; and 45\u0026deg;/-45\u0026deg;) on the mechanical properties, fracture resistance, and thermal stability of FDM-printed composites. PLA, PLA-CF, and PLA-GF, each reinforced with 20 wt% short carbon or glass fibers, were analyzed. Tensile, flexural, and fracture toughness (K\u003csub\u003eIC\u003c/sub\u003e, G\u003csub\u003eIC\u003c/sub\u003e, P\u003csub\u003eQ\u003c/sub\u003e) tests were performed according to ASTM standards, along with thermogravimetric analysis (TGA), porosity measurements, and fracture surface characterization using scanning electron microscopy (SEM). PLA exhibited the highest tensile strength in a 45\u0026deg;/-45\u0026deg; orientation (50.83 MPa), while PLA-GF in 0\u0026deg;/90\u0026deg; showed the highest flexural strength (17.79 MPa). Fracture resistance followed a similar trend, with PLA-GF achieving the highest K\u003csub\u003eIC\u003c/sub\u003e (4.71 MPa\u0026middot;m\u0026sup1;/\u0026sup2;) and P\u003csub\u003eQ\u003c/sub\u003e (1186.66 N), while PLA exhibited the highest G\u003csub\u003eIC\u003c/sub\u003e (10.31 kJ/m\u0026sup2;). Fractographic analysis revealed fiber pull-out and interfacial debonding, indicating differences in fiber-matrix adhesion. TGA confirmed a higher thermal stability for PLA-CF, while porosity analysis demonstrated a direct correlation between void content and mechanical performance. These findings emphasize the role of fiber type, printing orientation, and microstructural integrity in the mechanical behavior of FDM-printed composites, particularly for applications requiring enhanced fracture resistance.\u003c/p\u003e","manuscriptTitle":"Influence of Short Carbon and Glass Fibers on the Mechanical Performance, Thermal Stability, and Fracture Behavior of FDM-Printed Composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-22 13:21:58","doi":"10.21203/rs.3.rs-7336068/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Minor Revisions Needed","date":"2025-10-04T11:57:15+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-08-14T16:48:51+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-14T12:53:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-14T09:37:41+00:00","index":"","fulltext":""},{"type":"submitted","content":"The International Journal of Advanced Manufacturing Technology","date":"2025-08-12T14:36:43+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"43249cc1-839f-42b7-9cda-7cb13475ed67","owner":[],"postedDate":"August 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-20T16:03:59+00:00","versionOfRecord":{"articleIdentity":"rs-7336068","link":"https://doi.org/10.1007/s00170-025-16794-z","journal":{"identity":"the-international-journal-of-advanced-manufacturing-technology","isVorOnly":false,"title":"The International Journal of Advanced Manufacturing Technology"},"publishedOn":"2025-10-16 15:57:15","publishedOnDateReadable":"October 16th, 2025"},"versionCreatedAt":"2025-08-22 13:21:58","video":"","vorDoi":"10.1007/s00170-025-16794-z","vorDoiUrl":"https://doi.org/10.1007/s00170-025-16794-z","workflowStages":[]},"version":"v1","identity":"rs-7336068","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7336068","identity":"rs-7336068","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}