Effect of Nozzle Diameter on Mechanical Properties and Microstructure of Fused Deposition Modeling 3D Printed Polylactic Acid Parts

Effect of Nozzle Diameter on Mechanical Properties and Microstructure of Fused Deposition Modeling 3D Printed Polylactic Acid Parts | 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 Effect of Nozzle Diameter on Mechanical Properties and Microstructure of Fused Deposition Modeling 3D Printed Polylactic Acid Parts Pezhman Taghipour Birgani, Hatam Hardani This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7953803/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Fused deposition modeling (FDM) is one of the most common additive manufacturing techniques, but the mechanical performance of 3D printed components depends strongly on printing parameters. This study investigates the effects of nozzle diameter on tensile strength, elastic modulus, and microstructure in 3D printed polylactic acid (PLA) specimens. Samples were fabricated using a range of nozzle sizes from 0.2mm to 0.5mm diameter and tested under uniaxial tensile loading until failure. The results show an increase in ultimate tensile strength and Young's modulus with increasing nozzle diameter. Scanning electron microscopy reveals enhanced interlayer adhesion for larger nozzle sizes, with a transition in fracture mode from interlayer to intralayer dominated. To further understand these findings, anisotropic constitutive models were developed to predict the mechanical properties of PLA. These models were derived using principles of composite laminate theory, which consider the effects of nozzle diameter on the material coherence between printed layers. The theoretical predictions made by these models were compared with the experimental data, showing a good agreement and providing deeper insight into the relationship between printing parameters and mechanical performance. The experimental and analytical results both highlight nozzle diameter as a critical factor determining achievable mechanical properties in FDM. This work provides insights into the key relationships between processing, structure, and properties, which can guide component design and process optimization in 3D printing of thermoplastic polymers. Nozzle diameter Polylactic acid (PLA) Tensile strength Young's modulus Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction The concept of 3D printing technology was initially proposed by Charles W. Hull 35 years ago [ 1 – 3 ]. This novel additive manufacturing technique enables the creation of objects from digitized models without relying on traditional and expensive cutting or casting machines [ 4 – 8 ]. The technology's superiority in producing complex-shaped and multi-material components over other manufacturing methods has been well-documented in literature [9–13]. Additionally, 3D printing allows for significant raw material savings during the printing process. As a result, 3D printed components have found applications in various fields such as biomedicine [ 14 – 16 ], aerospace [ 14 , 17 ], automotive engineering [ 18 ], civil engineering [ 19 ], and even food [ 20 ]. There are several 3D printing techniques available, with the four most common ones being stereolithographic (SLA) [ 21 ], fused deposition modeling (FDM) [ 22 ], selective laser melting (SLM) [ 23 ], and selective laser sintering (SLS) [ 24 ]. Among these, FDM, developed by Stratasys Inc., has become one of the most well-known 3D printing techniques globally. FDM builds objects layer by layer, resulting in anisotropic mechanical properties [ 22 ]. In the FDM process, raw materials are extruded into the nozzle and converted from a filament state to a semi-liquid state. The semi-liquid material is then deposited onto the previous layer and cooled, solidified, and integrated with the surrounding materials. After a layer is completed, the platform supporting the object moves down by the height of one layer, and the next layer is printed. Mohan et al. [ 25 ] conducted a review of the optimization of materials and process parameters for FDM, revealing that thermoplastic materials such as PLA, ABS, metal matrix composites, ceramic composites, and natural fiber-reinforced composites are widely used in FDM printers. Despite the numerous advantages of 3D printing technology in producing complex or multi-material parts, its usage is limited by the insufficient knowledge on the mechanical properties of 3D printed parts. For example, the elastic constants and strength are critical in designing load-bearing components or structures. Thus, various studies have been conducted to investigate the mechanical properties of 3D printed parts to extend and accelerate the engineering application of 3D printing technology. These studies can be broadly divided into two categories. In 2018, Perez conducted a study on how layer height affects the surface roughness of 3D printed products. The study utilized PLA materials with a printing temperature of 220∘C and nozzle diameter of 0.4 mm. According to the results, reducing the layer height leads to improved surface roughness quality. Additionally, thinner wall thickness was found to result in smoother wall surfaces [ 26 ]. Setiawan conducted a study on the impact of 3D printing parameters on product quality, using PLA material to create products of ASTM D638 standard size and shape. The research found that the ideal printing speed and nozzle temperature were 80 mm/s and 220∘C, respectively, resulting in a tensile strength of 27.96 MPa for the PLA product. However, this parameter setting also resulted in 1.4% shrinkage [ 27 ]. Liang has identified a natural inflow angle of 75° for rubber and recommends using a nozzle with a cone angle similar to this angle to minimize extrusion forces and die swell [ 28 , 29 ]. Mackay et al. have conducted a comprehensive study of the liquefier's performance and determined characteristic rheological parameters for three polymers [ 30 ]. They have also developed an analytical model for predicting maximum extrusion velocity for different geometries and polymers using a fixed nozzle cone angle of 43.3°. Osswald et al. present a different model in which filament is only molten at the surface of the cone, which only applies for high filament feed velocities [ 31 , 32 ]. The main parameters for investigating the liquefying process are cone angle (α) and capillary length (L2), and the material of the nozzle is an aspect that has not been previously investigated [ 30 ]. Available nozzles are made of brass, steel, or a combination of both, with brass being widely used due to its good thermal conductivity. However, coated nozzles exhibit better wear resistance, especially when fiber-filled materials are used. Steel or tungsten, which have a higher hardness, can be used without coating, but have drawbacks such as low thermal conductivity or being difficult to machine [ 33 , 34 ]. The conical section and the capillary leading to the orifice are areas with the highest shear stress and wear, which can be mitigated by using an insert made of materials such as ruby, sapphire, or diamond [ 35 – 37 ]. Further experimental investigation is needed to validate the analytical models, especially for a wider range of nozzle cone angles and diameters. The present study examined the diameter hole size of the nozzle as a crucial process parameter in 3D printing that affects product properties. To represent physical and mechanical characteristics, density and tensile strength were chosen as key parameters. The tensile strength was determined by subjecting the products to axial tensile loading until they fractured. 2. Materials and Methods 2.1. FDM AM specimens 2.1.1. Dimension of specimens The size of the objects being tested was determined based on ASTM D638 type 1, an international standard for measuring the tensile properties of plastics through molding and extrusion. The specific 3D printing specimen model used in the study can be seen in Fig. 1. Figure. 1. The geometric model of 3D printing specimen for uniaxial tensile test. 2.1.1. Material and FDM AM machine Specimens used for tensile testing were printed with fused deposition modeling additive manufacturing using an Alpha 3D printer from Ala Miad Negin Iran. The printer uses polylactic acid (PLA) thermoplastic filament. The printer has a single nozzle tip for extruding the material. Printing parameters like layer thickness, print speed, and infill percentage were set in the slicing software. Based on printing speed and desired mechanical properties, nozzle diameter of 0.2mm, 0.3mm, 0.4mm and 0.5mm and layer thicknesses 0.2mm were used for the tensile specimens. The PLA filament was heated to 215°C during printing. The PLA filament was supplied by Alpha 3D Printer. The properties of the raw PLA material are provided in Table 1 . Table 1 Printing parameters Printing parameter Value Layer thickness 0.2mm Nozzle temperature 215 ∘ C Printing speed 3000 mm/min Infill percentage 50% Infill pattern Grid 2.1.2. Displaying Specimen Dimensions and Print Status FDM AM samples were specifically created based on ASTM D638 type 1 (an international standard for determining the tensile properties of plastics, including test conditions for molding and extrusion). PLA filament was heated to 215°C during printing. To accurately assess the impact of printing nozzle diameter on tensile strength and Young's modulus, specimens with varying hole nozzle (0.2mm, 0.3mm, 0.4mm and 0.5mm) were utilized in the experiment Fig. 3 . While printing, samples were printed in four different nozzle diameters and two conditions, with and without a bed which are shown in Fig. 4. 2.2. Exploring the Uniaxial Tensile Properties of FDM AM PLA Material Tensile tests are conducted to examine the FDM AM PLA material's tensile strength and Young's modulus. The test is performed using a computer-controlled electronic universal tensile test machine Santam brand from IAU Ahvaz branch, Iran. The test is carried out at a speed of 5 mm/min and at a temperature of 23°C, ensuring standard experimental conditions. The equipment is illustrated in Fig. 4. Figure. 4. uniaxial tensile test device. 2.3. Fracture results Figure 5 displays the fracture outcomes of the tested specimens used to assess the tensile strength of FDM AM PLA material. When the printing nozzle diameter are set 0.5mm, the fracture surfaces exhibit a parallel orientation to the material layers, indicating an "Inter-Layer Fracture Mode." Conversely, at printing 0.2mm, 0.3mm and 0.4mm nozzle diameter, the fracture surfaces show unique angles in relation to the material layers, indicating an "In-Layer Fracture Mode. 3. Results and discussions 3.1. Tensile strength test data of FDM AM PLA material During the examination of tensile strength, 25 samples are printed and subjected to stretching until failure. The results, as shown in Table 2 , indicate a notable trend: tensile strength rises as the nozzle diameter increases. Particularly, the material printed with a nozzle diameter of 0.5mm and a layer thickness of 0.25mm, exhibits the highest tensile strength at 23.78 MPa. In contrast, the material printed with a 0.2mm printing angle and 0.25mm layer thickness shows the lowest tensile strength at 15.40 MPa. The difference between these two strengths is significant at 8.38 MPa, which stands out compared to other data points. Consequently, the nozzle diameter has a significant impact on tensile strength, as supported by the corresponding results presented in Fig. 5 Table 2 Tensile strength test data for the FDM AM PLA material (unit: MPa). Sample No. Sut Mean *21x 16.20 15.70 22x 15.83 23x 15.40 24x 15.65 25x 15.48 31x 19.99 19.77 32x 19.28 33x 19.45 34x 19.98 35x 20.16 41x 19.63 20.04 42x 19.89 43x 20.52 44x 20.16 45x 19.98 51x 23.78 22.90 52x 23.08 53x 23.17 54x 22.11 55x 22.37 *The first number refers to the nozzle diameter, and the second number refers to the sample number from that same nozzle. 3.2. Elastic property of FDM AM PLA material This research studied the elastic property of 20 fabricated specimens. The Young's Modulus test data for these specimens is provided in Table 3 . The mean test data shows that the Young's Modulus increases as the nozzle diameter grows from 0.2mm to 0.5mm. The specimens with a 0.5mm nozzle diameter have the highest Young's Modulus test measurement at 761.72 MPa. Additionally, the specimens printed at 0.2mm nozzle diameter have the lowest Young's Modulus measurement at 540.08 MPa. The difference between the highest and lowest Young's Modulus values is 221.64 MPa. Therefore, the results indicate that the nozzle diameter significantly influences the Young's Modulus. This is further evidenced by the results graphed in Fig. 6 . Table 3 Young's Modulus test data for the FDM AM PLA material (unit: MPa). Sample No. Young's Modulus Mean 21x 568.60 561.21 22x 572.38 23x 565.67 24x 559.34 25x 540.08 31x 693.16 676.42 32x 685.01 33x 670.02 34x 669.92 35x 664.01 41x 671.17 681.51 42x 695.30 43x 684.54 44x 670.70 45x 685.86 51x 754.52 748.74 52x 744.60 53x 761.72 54x 726.67 55x 756.17 3.3. Comparison between theoretical results and test data In this study, anisotropic constitutive models were developed to predict the tensile strength and Young's modulus of 3D printed PLA components. These models were derived based on the principles of composite laminate theory, which takes into account the material behavior between printed rasters and layers. The model considers the influence of nozzle diameter on the material coherence and adhesion between the printed layers, which significantly impacts the mechanical properties. The theoretical formulation involves the transformation of material axes to account for the anisotropic nature of the printed materials. The model's predictions were compared with the experimental results, and a good agreement was observed. The following equations represent the relationship between nozzle diameter and the mechanical properties of PLA: $$\:{\phi\:}=1-\left(\frac{\left(\frac{\pi\:}{4}{H}^{2}\right)+H.(D-H)}{D.H}\right)$$ Figures 7 and 8 illustrate the comparison between the experimental results and the theoretical predictions, while Table 4 summarizes the relative errors between the two sets of data. The comparisons between the theoretical results and experimental test data are presented in Figs. 7 and 8 These figures show that the theoretical models developed in Section 3 exhibit good agreement with and predictability of the test data. The relative errors between the theoretical and measured tensile strengths are provided in Table 4 . Most of the error values are less than 11%. The tensile strength test results for the 0.2mm and 0.5mm nozzle diameters were used as parameters in the strength theoretical model. As such, the theoretical results match the test data for these two nozzle sizes. Based on the quantitative evaluation in Table 4 and the data shown in Fig. 9 , the predictive capability of the tensile strength theoretical model formulated in this study is validated. Figure 7. Tensile strength test data comparison between different layer thickness. Table 4 Relative Error between theoretical results and test data (%). Tensile strengthYoung's Modulus Nozzle diameter = 0.2mm 11 8.6 Nozzle diameter = 0.3mm 9 9 Nozzle diameter = 0.4mm 10.5 10.3 Nozzle diameter = 0.5mm 9.3 8.9 3.4. Mechanical properties Examination of the stress-strain curves indicates a positive correlation between nozzle diameter and ultimate tensile strength of the 3D printed polylactic acid (PLA) parts, with components fabricated utilizing larger nozzles exhibiting improved strength capacity compared to those produced with smaller diameters. Several factors potentially contribute to this overarching trend. The larger nozzle extrusion width lays down wider filament beads, promoting enhanced inter-layer adhesion and bonding between the successive material rasters and slices. Additionally, the tendency for smaller nozzles to leave microvoids or gaps between filament strands is reduced with increasing nozzle size, minimizing stress concentrations within the layers that can precipitate premature failure. The increased material deposition rate from larger nozzles also serves to slow the cooling kinetics of the PLA, enabling better crystallization and molecular ordering that improves strength. However, this strength gain comes at the cost of part ductility and flexibility, as evidenced by the strain at break measurements decreasing in conjunction with rising nozzle diameter. This implies a more brittle fracture response and reduced capacity for elastic deformation prior to failure when utilizing larger nozzle sizes, likely resulting from increased inter-layer rigidity and restricted localized shear motions between raster beads. Specific quantification of the incremental differences in achievable tensile strength and failure strain between varying nozzle sizes remains ambiguous without additional empirical data points. Nevertheless, the overarching experimental trends provide a qualitative basis for informed selection of printing parameters tailored to application requirements. While larger nozzles promote maximize load-bearing capacity, smaller diameters confer superior flexibility. Optimization of factors such as air gap, raster orientation, print temperature profile, and environmental conditions could further elucidate the relative implications of nozzle size choice. The best nozzle diameter for a specific application will depend on the particular needs of the part. If strength is the main criterion, then a larger nozzle might be better. However, if flexibility is essential, then a smaller nozzle might be more suitable. 3.5 SEM Images The Scanning Electron Microscope (SEM) images of a parts made with a PLA 3D printer Fig. 10 shows the microscopic structure of the printed material, revealing details that are not visible to the naked eye. The image displays elongated and closely packed structures resembling fibrous strands or tubes. These are likely due to the 3D printing extrusion process, where the PLA filament is melted and deposited layer by layer to form the part. There are broken or fractured surfaces visible, exposing the internal structure which appears porous and layered. These indicate the presence of defects or weaknesses in the material, which could affect its mechanical properties and performance. The fractures could be caused by external factors such as stress, temperature, or humidity, or by internal factors such as impurities, air bubbles, or poor adhesion between layers. The magnification is 300x as indicated on the image, providing a close-up view to analyze material properties and quality. A higher magnification could reveal more details about the surface morphology and texture, while a lower magnification could show the overall shape and dimensions of the part. A scale bar at the bottom left indicates that 200µm actually corresponds to the width of the image. This means that the image covers a small area of the part, and may not represent the whole material. To get a more comprehensive analysis, multiple images from different regions and angles of the part could be taken and compared. The image also contains some metadata from the SEM device, such as the working distance, the signal type, the current, the date, and the time. These parameters could affect the quality and resolution of the image, and should be taken into account when interpreting the results. Surface texture : The surface of the part is rough and uneven, with striations and ridges visible. This is likely due to the layer-by-layer nature of the 3D printing process, where molten plastic is deposited in thin lines. The roughness of the surface can affect the part's strength, wear resistance, and other properties. Porosity : There appear to be some small pores or voids in the surface of the part. These pores can be caused by air bubbles trapped in the molten plastic during printing, or by incomplete fusion between layers. The presence of pores can weaken the part and make it more susceptible to cracks and other failures. Cracks : There are a few small cracks visible in the surface of the part. These cracks could be caused by thermal stresses induced during printing, or by mechanical stresses during use. Cracks can significantly weaken the part and lead to failure. Overall, the SEM image suggests that the 3D printed part is of moderate quality. The rough surface texture and presence of pores could potentially affect the part's performance. It is important to optimize the printing process parameters to minimize these defects and ensure the part meets the required functional specifications. 4. Conclusions This study show that nozzle diameter is a critical determinant of tensile strength and elastic modulus in fused deposition modeling (FDM) 3D printed polylactic acid (PLA) components. The effect of nozzle diameter on the tensile strength of PLA parts printed by 3D printer was specifically examined. The results indicate that the tensile strength increases as the nozzle diameter increases, with the highest tensile strength observed for the 0.5mm nozzle diameter. Similarly, the Young's modulus also increases as the nozzle diameter increases, with the highest modulus observed for the 0.5mm nozzle diameter. As nozzle size increases incrementally from 0.2mm to 0.5mm, substantial improvements in both ultimate tensile strength and Young's modulus are achieved. The presented constitutive models, derived from fundamental composite laminate theory and transformation of material axes, show excellent agreement with experimental data. This verifies their validity and predictive capability to enable optimization of the 3D printing process through tailored nozzle selection. Analysis of fracture surfaces indicates a transition in failure mode, from inter-layer dominated cracks at small nozzle diameters toward in-layer failures in parts produced with the 0.5mm nozzle. This suggests larger extrusion widths promote improved inter-raster adhesion within and between printed layers. However, enhanced stiffness and load-bearing capacity comes at the cost of reduced ductility, as evidenced by decreased strain to failure in tension for the maximum nozzle size. Determination of an optimal nozzle configuration is thus application-specific, dictated by requirements for strength, impact resistance, durability, and flexibility. While providing initial insights into property-process relationships, the current preliminary study was limited to PLA and a narrow range of nozzle diameters under static loading. Ongoing work seeks to expand the experimental dataset and model calibration to additional materials, nozzle dimensions, dynamic loads, and multi-axial stress states. Nonetheless, the framework established here facilitates purposeful design of 3D printed components with tailored mechanical performance. Declarations Author Contribution Both authors contributed equally to the conceptualization, experimental work, data analysis, and writing of the manuscript. Both authors reviewed and approved the final manuscript. References Hull CW (1984) Apparatus for production of three-dimensional objects by stereolithography Hull CW, Spence ST, Albert DJ, Smalley DR, Harlow RA, Stinebaugh P et al (1999) Method and apparatus for production of high resolution three-dimensional objects by stereolithography Hull CW (2015) The birth of 3D printing. 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12:33:36","extension":"xml","order_by":23,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":82272,"visible":true,"origin":"","legend":"","description":"","filename":"01813859dda6407ab615305f0d0dfbdc1structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/3047a0345a1998db8bb24561.xml"},{"id":96823871,"identity":"09082600-b560-479e-a9fd-0b0c259bac2d","added_by":"auto","created_at":"2025-11-26 12:33:36","extension":"html","order_by":24,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":89928,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/5546a160086c211c376f9f29.html"},{"id":96918962,"identity":"795f9c23-8732-404d-ba71-562264eeb7ec","added_by":"auto","created_at":"2025-11-27 14:12:54","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":12031,"visible":true,"origin":"","legend":"\u003cp\u003eThe geometric model of 3D printing specimen for uniaxial tensile test.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/a7adb25aa827797baaf7e6d3.png"},{"id":96917171,"identity":"6f06870d-81a1-4f47-a866-f5e8c35559b2","added_by":"auto","created_at":"2025-11-27 14:09:20","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":36291,"visible":true,"origin":"","legend":"\u003cp\u003eThe printed model of 3D printing specimen for uniaxial tensile test.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/45fe22283db94469f6e22726.jpeg"},{"id":96823848,"identity":"a4d7e785-2472-41dd-9d18-590d3ed07b93","added_by":"auto","created_at":"2025-11-26 12:33:36","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":15538,"visible":true,"origin":"","legend":"\u003cp\u003eHole nozzle diameters were utilized in the experiment.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/aeeadbdedc2895fa0e9beb07.jpeg"},{"id":96917894,"identity":"ab108d5d-4273-40f2-8407-7729a04d6a15","added_by":"auto","created_at":"2025-11-27 14:10:42","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":29216,"visible":true,"origin":"","legend":"\u003cp\u003euniaxial tensile test device.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/e7453737ff28eaf6be53914d.jpeg"},{"id":96916831,"identity":"85a9faa8-e5cd-4c0e-9641-cd4fc391b7c2","added_by":"auto","created_at":"2025-11-27 14:08:56","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":20799,"visible":true,"origin":"","legend":"\u003cp\u003eTensile strength test data comparison between different nozzle diameter\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/03b3511275b674b96234fa56.jpeg"},{"id":96823853,"identity":"d2308b35-ba9b-4053-98dd-d474fd587803","added_by":"auto","created_at":"2025-11-26 12:33:36","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":207072,"visible":true,"origin":"","legend":"\u003cp\u003eYoung's Modulus test data for the FDM AM PLA material.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/1a6e9de696a56b02289e8c2c.jpeg"},{"id":96917501,"identity":"9e8930f1-9657-4000-a63d-0d53a149bcfe","added_by":"auto","created_at":"2025-11-27 14:09:53","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":32943,"visible":true,"origin":"","legend":"\u003cp\u003eTensile strength test data comparison between different layer thickness.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/5d7c1bb52fa7fae4a5a9c5f5.jpeg"},{"id":96918450,"identity":"8f3720ca-2f42-45ab-bd1f-a4b3b6c6bd96","added_by":"auto","created_at":"2025-11-27 14:11:57","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":31548,"visible":true,"origin":"","legend":"\u003cp\u003eYoung's Modulus test data comparison between different layer thickness.\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/8049cd92abf4713db5a80f07.jpeg"},{"id":96823863,"identity":"16abb11a-f7bb-47d6-a809-6645904c7248","added_by":"auto","created_at":"2025-11-26 12:33:36","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":23483,"visible":true,"origin":"","legend":"\u003cp\u003eStress-elongation diagram of the samples with different 3D printing nozzles\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/0fb40b8e75c31ce9671c317c.jpeg"},{"id":96918027,"identity":"f7e5e960-ff49-496b-8092-dc22f114b089","added_by":"auto","created_at":"2025-11-27 14:11:01","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1604348,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the specimen created by nozzle with diameter of (a) 0.2 mm, (b) 0.3 mm, (c) 0.4 mm, (d) 0.5 mm\u003c/p\u003e","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/f49f263c226dfa3f7ba33f9d.jpeg"},{"id":100356310,"identity":"5d33c5ab-87aa-494d-8e6f-0214a82f1fa6","added_by":"auto","created_at":"2026-01-16 07:02:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2701376,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7953803/v1/3e1b99a0-0acc-49ed-a220-ae0866f37666.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Nozzle Diameter on Mechanical Properties and Microstructure of Fused Deposition Modeling 3D Printed Polylactic Acid Parts","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe concept of 3D printing technology was initially proposed by Charles W. Hull 35 years ago [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. This novel additive manufacturing technique enables the creation of objects from digitized models without relying on traditional and expensive cutting or casting machines [\u003cspan additionalcitationids=\"CR5 CR6 CR7\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The technology's superiority in producing complex-shaped and multi-material components over other manufacturing methods has been well-documented in literature [9\u0026ndash;13]. Additionally, 3D printing allows for significant raw material savings during the printing process. As a result, 3D printed components have found applications in various fields such as biomedicine [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR13\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e16\u003c/span\u003e], aerospace [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e17\u003c/span\u003e], automotive engineering [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e18\u003c/span\u003e], civil engineering [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e19\u003c/span\u003e], and even food [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThere are several 3D printing techniques available, with the four most common ones being stereolithographic (SLA) [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e21\u003c/span\u003e], fused deposition modeling (FDM) [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e22\u003c/span\u003e], selective laser melting (SLM) [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e23\u003c/span\u003e], and selective laser sintering (SLS) [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Among these, FDM, developed by Stratasys Inc., has become one of the most well-known 3D printing techniques globally. FDM builds objects layer by layer, resulting in anisotropic mechanical properties [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In the FDM process, raw materials are extruded into the nozzle and converted from a filament state to a semi-liquid state. The semi-liquid material is then deposited onto the previous layer and cooled, solidified, and integrated with the surrounding materials. After a layer is completed, the platform supporting the object moves down by the height of one layer, and the next layer is printed. Mohan et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e25\u003c/span\u003e] conducted a review of the optimization of materials and process parameters for FDM, revealing that thermoplastic materials such as PLA, ABS, metal matrix composites, ceramic composites, and natural fiber-reinforced composites are widely used in FDM printers.\u003c/p\u003e\u003cp\u003eDespite the numerous advantages of 3D printing technology in producing complex or multi-material parts, its usage is limited by the insufficient knowledge on the mechanical properties of 3D printed parts. For example, the elastic constants and strength are critical in designing load-bearing components or structures. Thus, various studies have been conducted to investigate the mechanical properties of 3D printed parts to extend and accelerate the engineering application of 3D printing technology. These studies can be broadly divided into two categories.\u003c/p\u003e\u003cp\u003eIn 2018, Perez conducted a study on how layer height affects the surface roughness of 3D printed products. The study utilized PLA materials with a printing temperature of 220∘C and nozzle diameter of 0.4 mm. According to the results, reducing the layer height leads to improved surface roughness quality. Additionally, thinner wall thickness was found to result in smoother wall surfaces [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eSetiawan conducted a study on the impact of 3D printing parameters on product quality, using PLA material to create products of ASTM D638 standard size and shape. The research found that the ideal printing speed and nozzle temperature were 80 mm/s and 220∘C, respectively, resulting in a tensile strength of 27.96 MPa for the PLA product. However, this parameter setting also resulted in 1.4% shrinkage [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eLiang has identified a natural inflow angle of 75\u0026deg; for rubber and recommends using a nozzle with a cone angle similar to this angle to minimize extrusion forces and die swell [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Mackay et al. have conducted a comprehensive study of the liquefier's performance and determined characteristic rheological parameters for three polymers [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. They have also developed an analytical model for predicting maximum extrusion velocity for different geometries and polymers using a fixed nozzle cone angle of 43.3\u0026deg;. Osswald et al. present a different model in which filament is only molten at the surface of the cone, which only applies for high filament feed velocities [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The main parameters for investigating the liquefying process are cone angle (α) and capillary length (L2), and the material of the nozzle is an aspect that has not been previously investigated [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Available nozzles are made of brass, steel, or a combination of both, with brass being widely used due to its good thermal conductivity. However, coated nozzles exhibit better wear resistance, especially when fiber-filled materials are used. Steel or tungsten, which have a higher hardness, can be used without coating, but have drawbacks such as low thermal conductivity or being difficult to machine [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The conical section and the capillary leading to the orifice are areas with the highest shear stress and wear, which can be mitigated by using an insert made of materials such as ruby, sapphire, or diamond [\u003cspan additionalcitationids=\"CR36\" citationid=\"CR34\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Further experimental investigation is needed to validate the analytical models, especially for a wider range of nozzle cone angles and diameters.\u003c/p\u003e\u003cp\u003eThe present study examined the diameter hole size of the nozzle as a crucial process parameter in 3D printing that affects product properties. To represent physical and mechanical characteristics, density and tensile strength were chosen as key parameters. The tensile strength was determined by subjecting the products to axial tensile loading until they fractured.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. FDM AM specimens\u003c/h2\u003e\u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\u003ch2\u003e2.1.1. Dimension of specimens\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe size of the objects being tested was determined based on ASTM D638 type 1, an international standard for measuring the tensile properties of plastics through molding and extrusion. The specific 3D printing specimen model used in the study can be seen in Fig.\u0026nbsp;1.\u003c/p\u003e\u003cp\u003eFigure. 1. The geometric model of 3D printing specimen for uniaxial tensile test.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.1.1. Material and FDM AM machine\u003c/h2\u003e\u003cp\u003eSpecimens used for tensile testing were printed with fused deposition modeling additive manufacturing using an Alpha 3D printer from Ala Miad Negin Iran. The printer uses polylactic acid (PLA) thermoplastic filament. The printer has a single nozzle tip for extruding the material. Printing parameters like layer thickness, print speed, and infill percentage were set in the slicing software. Based on printing speed and desired mechanical properties, nozzle diameter of 0.2mm, 0.3mm, 0.4mm and 0.5mm and layer thicknesses 0.2mm were used for the tensile specimens. The PLA filament was heated to 215\u0026deg;C during printing. The PLA filament was supplied by Alpha 3D Printer. The properties of the raw PLA material are provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\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\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrinting parameter\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eValue\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLayer thickness\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.2mm\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\u003e215 \u003csup\u003e∘\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePrinting speed\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3000 mm/min\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInfill percentage\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50%\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInfill pattern\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eGrid\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.1.2. Displaying Specimen Dimensions and Print Status\u003c/h2\u003e\u003cp\u003eFDM AM samples were specifically created based on ASTM D638 type 1 (an international standard for determining the tensile properties of plastics, including test conditions for molding and extrusion). PLA filament was heated to 215\u0026deg;C during printing. To accurately assess the impact of printing nozzle diameter on tensile strength and Young's modulus, specimens with varying hole nozzle (0.2mm, 0.3mm, 0.4mm and 0.5mm) were utilized in the experiment Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e. While printing, samples were printed in four different nozzle diameters and two conditions, with and without a bed which are shown in Fig.\u0026nbsp;4.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Exploring the Uniaxial Tensile Properties of FDM AM PLA Material\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTensile tests are conducted to examine the FDM AM PLA material's tensile strength and Young's modulus. The test is performed using a computer-controlled electronic universal tensile test machine Santam brand from IAU Ahvaz branch, Iran. The test is carried out at a speed of 5 mm/min and at a temperature of 23\u0026deg;C, ensuring standard experimental conditions. The equipment is illustrated in Fig.\u0026nbsp;4.\u003c/p\u003e\u003cp\u003eFigure. 4. uniaxial tensile test device.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Fracture results\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e5\u003c/span\u003e displays the fracture outcomes of the tested specimens used to assess the tensile strength of FDM AM PLA material. When the printing nozzle diameter are set 0.5mm, the fracture surfaces exhibit a parallel orientation to the material layers, indicating an \"Inter-Layer Fracture Mode.\" Conversely, at printing 0.2mm, 0.3mm and 0.4mm nozzle diameter, the fracture surfaces show unique angles in relation to the material layers, indicating an \"In-Layer Fracture Mode.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussions","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Tensile strength test data of FDM AM PLA material\u003c/h2\u003e\u003cp\u003eDuring the examination of tensile strength, 25 samples are printed and subjected to stretching until failure. The results, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, indicate a notable trend: tensile strength rises as the nozzle diameter increases. Particularly, the material printed with a nozzle diameter of 0.5mm and a layer thickness of 0.25mm, exhibits the highest tensile strength at 23.78 MPa. In contrast, the material printed with a 0.2mm printing angle and 0.25mm layer thickness shows the lowest tensile strength at 15.40 MPa. The difference between these two strengths is significant at 8.38 MPa, which stands out compared to other data points. Consequently, the nozzle diameter has a significant impact on tensile strength, as supported by the corresponding results presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e5\u003c/span\u003e\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\u003eTensile strength test data for the FDM AM PLA material (unit: MPa).\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=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample No.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSut\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMean\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e*21x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e16.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e15.70\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e22x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e15.83\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e23x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e15.40\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e24x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e15.65\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e25x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e15.48\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e31x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.99\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e19.77\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e32x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.28\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e33x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.45\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e34x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.98\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e35x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e20.16\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e41x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e20.04\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e42x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.89\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e43x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e20.52\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e44x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e20.16\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e45x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.98\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e51x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e23.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e22.90\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e52x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e23.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e53x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e23.17\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e54x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e22.11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e55x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e22.37\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\u003e*The first number refers to the nozzle diameter, and the second number refers to the sample number from that same nozzle.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Elastic property of FDM AM PLA material\u003c/h2\u003e\u003cp\u003eThis research studied the elastic property of 20 fabricated specimens. The Young's Modulus test data for these specimens is provided in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The mean test data shows that the Young's Modulus increases as the nozzle diameter grows from 0.2mm to 0.5mm. The specimens with a 0.5mm nozzle diameter have the highest Young's Modulus test measurement at 761.72 MPa. Additionally, the specimens printed at 0.2mm nozzle diameter have the lowest Young's Modulus measurement at 540.08 MPa. The difference between the highest and lowest Young's Modulus values is 221.64 MPa. Therefore, the results indicate that the nozzle diameter significantly influences the Young's Modulus. This is further evidenced by the results graphed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e6\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\u003eYoung's Modulus test data for the FDM AM PLA material (unit: MPa).\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=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample No.\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eYoung's Modulus\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMean\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e21x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e568.60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e561.21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e22x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e572.38\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e23x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e565.67\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e24x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e559.34\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e25x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e540.08\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e31x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e693.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e676.42\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e32x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e685.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e33x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e670.02\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e34x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e669.92\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e35x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e664.01\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e41x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e671.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e681.51\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e42x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e695.30\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e43x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e684.54\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e44x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e670.70\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e45x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e685.86\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e51x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e754.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e748.74\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e52x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e744.60\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e53x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e761.72\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e54x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e726.67\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e55x\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e756.17\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\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Comparison between theoretical results and test data\u003c/h2\u003e\u003cp\u003eIn this study, anisotropic constitutive models were developed to predict the tensile strength and Young's modulus of 3D printed PLA components. These models were derived based on the principles of composite laminate theory, which takes into account the material behavior between printed rasters and layers. The model considers the influence of nozzle diameter on the material coherence and adhesion between the printed layers, which significantly impacts the mechanical properties.\u003c/p\u003e\u003cp\u003eThe theoretical formulation involves the transformation of material axes to account for the anisotropic nature of the printed materials. The model's predictions were compared with the experimental results, and a good agreement was observed. The following equations represent the relationship between nozzle diameter and the mechanical properties of PLA:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:{\\phi\\:}=1-\\left(\\frac{\\left(\\frac{\\pi\\:}{4}{H}^{2}\\right)+H.(D-H)}{D.H}\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFigures 7 and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e8\u003c/span\u003e illustrate the comparison between the experimental results and the theoretical predictions, while Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e summarizes the relative errors between the two sets of data.\u003c/p\u003e\u003cp\u003eThe comparisons between the theoretical results and experimental test data are presented in Figs.\u0026nbsp;7 and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e8\u003c/span\u003e These figures show that the theoretical models developed in Section \u003cspan refid=\"Sec9\" class=\"InternalRef\"\u003e3\u003c/span\u003e exhibit good agreement with and predictability of the test data.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe relative errors between the theoretical and measured tensile strengths are provided in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Most of the error values are less than 11%. The tensile strength test results for the 0.2mm and 0.5mm nozzle diameters were used as parameters in the strength theoretical model. As such, the theoretical results match the test data for these two nozzle sizes. Based on the quantitative evaluation in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and the data shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e9\u003c/span\u003e, the predictive capability of the tensile strength theoretical model formulated in this study is validated.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;7. Tensile strength test data comparison between different layer thickness.\u003c/p\u003e\u003cp\u003e\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\u003eRelative Error between theoretical results and test data (%).\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTensile strengthYoung's Modulus\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNozzle diameter\u0026thinsp;=\u0026thinsp;0.2mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e11 8.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNozzle diameter\u0026thinsp;=\u0026thinsp;0.3mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e9 9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNozzle diameter\u0026thinsp;=\u0026thinsp;0.4mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10.5 10.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNozzle diameter\u0026thinsp;=\u0026thinsp;0.5mm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e9.3 8.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Mechanical properties\u003c/h2\u003e\u003cp\u003eExamination of the stress-strain curves indicates a positive correlation between nozzle diameter and ultimate tensile strength of the 3D printed polylactic acid (PLA) parts, with components fabricated utilizing larger nozzles exhibiting improved strength capacity compared to those produced with smaller diameters. Several factors potentially contribute to this overarching trend. The larger nozzle extrusion width lays down wider filament beads, promoting enhanced inter-layer adhesion and bonding between the successive material rasters and slices. Additionally, the tendency for smaller nozzles to leave microvoids or gaps between filament strands is reduced with increasing nozzle size, minimizing stress concentrations within the layers that can precipitate premature failure. The increased material deposition rate from larger nozzles also serves to slow the cooling kinetics of the PLA, enabling better crystallization and molecular ordering that improves strength. However, this strength gain comes at the cost of part ductility and flexibility, as evidenced by the strain at break measurements decreasing in conjunction with rising nozzle diameter. This implies a more brittle fracture response and reduced capacity for elastic deformation prior to failure when utilizing larger nozzle sizes, likely resulting from increased inter-layer rigidity and restricted localized shear motions between raster beads. Specific quantification of the incremental differences in achievable tensile strength and failure strain between varying nozzle sizes remains ambiguous without additional empirical data points. Nevertheless, the overarching experimental trends provide a qualitative basis for informed selection of printing parameters tailored to application requirements. While larger nozzles promote maximize load-bearing capacity, smaller diameters confer superior flexibility. Optimization of factors such as air gap, raster orientation, print temperature profile, and environmental conditions could further elucidate the relative implications of nozzle size choice. The best nozzle diameter for a specific application will depend on the particular needs of the part. If strength is the main criterion, then a larger nozzle might be better. However, if flexibility is essential, then a smaller nozzle might be more suitable.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.5 SEM Images\u003c/h2\u003e\u003cp\u003eThe Scanning Electron Microscope (SEM) images of a parts made with a PLA 3D printer Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the microscopic structure of the printed material, revealing details that are not visible to the naked eye.\u003c/p\u003e\u003cp\u003eThe image displays elongated and closely packed structures resembling fibrous strands or tubes. These are likely due to the 3D printing extrusion process, where the PLA filament is melted and deposited layer by layer to form the part.\u003c/p\u003e\u003cp\u003eThere are broken or fractured surfaces visible, exposing the internal structure which appears porous and layered. These indicate the presence of defects or weaknesses in the material, which could affect its mechanical properties and performance. The fractures could be caused by external factors such as stress, temperature, or humidity, or by internal factors such as impurities, air bubbles, or poor adhesion between layers.\u003c/p\u003e\u003cp\u003eThe magnification is 300x as indicated on the image, providing a close-up view to analyze material properties and quality. A higher magnification could reveal more details about the surface morphology and texture, while a lower magnification could show the overall shape and dimensions of the part.\u003c/p\u003e\u003cp\u003eA scale bar at the bottom left indicates that 200\u0026micro;m actually corresponds to the width of the image. This means that the image covers a small area of the part, and may not represent the whole material. To get a more comprehensive analysis, multiple images from different regions and angles of the part could be taken and compared.\u003c/p\u003e\u003cp\u003eThe image also contains some metadata from the SEM device, such as the working distance, the signal type, the current, the date, and the time. These parameters could affect the quality and resolution of the image, and should be taken into account when interpreting the results.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eSurface texture\u003c/b\u003e: The surface of the part is rough and uneven, with striations and ridges visible. This is likely due to the layer-by-layer nature of the 3D printing process, where molten plastic is deposited in thin lines. The roughness of the surface can affect the part's strength, wear resistance, and other properties.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003ePorosity\u003c/b\u003e: There appear to be some small pores or voids in the surface of the part. These pores can be caused by air bubbles trapped in the molten plastic during printing, or by incomplete fusion between layers. The presence of pores can weaken the part and make it more susceptible to cracks and other failures.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eCracks\u003c/b\u003e: There are a few small cracks visible in the surface of the part. These cracks could be caused by thermal stresses induced during printing, or by mechanical stresses during use. Cracks can significantly weaken the part and lead to failure.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eOverall, the SEM image suggests that the 3D printed part is of moderate quality. The rough surface texture and presence of pores could potentially affect the part's performance. It is important to optimize the printing process parameters to minimize these defects and ensure the part meets the required functional specifications.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study show that nozzle diameter is a critical determinant of tensile strength and elastic modulus in fused deposition modeling (FDM) 3D printed polylactic acid (PLA) components. The effect of nozzle diameter on the tensile strength of PLA parts printed by 3D printer was specifically examined. The results indicate that the tensile strength increases as the nozzle diameter increases, with the highest tensile strength observed for the 0.5mm nozzle diameter. Similarly, the Young's modulus also increases as the nozzle diameter increases, with the highest modulus observed for the 0.5mm nozzle diameter.\u003c/p\u003e\u003cp\u003eAs nozzle size increases incrementally from 0.2mm to 0.5mm, substantial improvements in both ultimate tensile strength and Young's modulus are achieved. The presented constitutive models, derived from fundamental composite laminate theory and transformation of material axes, show excellent agreement with experimental data. This verifies their validity and predictive capability to enable optimization of the 3D printing process through tailored nozzle selection. Analysis of fracture surfaces indicates a transition in failure mode, from inter-layer dominated cracks at small nozzle diameters toward in-layer failures in parts produced with the 0.5mm nozzle. This suggests larger extrusion widths promote improved inter-raster adhesion within and between printed layers. However, enhanced stiffness and load-bearing capacity comes at the cost of reduced ductility, as evidenced by decreased strain to failure in tension for the maximum nozzle size. Determination of an optimal nozzle configuration is thus application-specific, dictated by requirements for strength, impact resistance, durability, and flexibility.\u003c/p\u003e\u003cp\u003eWhile providing initial insights into property-process relationships, the current preliminary study was limited to PLA and a narrow range of nozzle diameters under static loading. Ongoing work seeks to expand the experimental dataset and model calibration to additional materials, nozzle dimensions, dynamic loads, and multi-axial stress states. Nonetheless, the framework established here facilitates purposeful design of 3D printed components with tailored mechanical performance.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eBoth authors contributed equally to the conceptualization, experimental work, data analysis, and writing of the manuscript. Both authors reviewed and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHull CW (1984) Apparatus for production of three-dimensional objects by stereolithography\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHull CW, Spence ST, Albert DJ, Smalley DR, Harlow RA, Stinebaugh P et al (1999) Method and apparatus for production of high resolution three-dimensional objects by stereolithography\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHull CW (2015) The birth of 3D printing. 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Mater Technol 47(6):715\u0026ndash;721\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Nozzle diameter, Polylactic acid (PLA), Tensile strength, Young's modulus","lastPublishedDoi":"10.21203/rs.3.rs-7953803/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7953803/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFused deposition modeling (FDM) is one of the most common additive manufacturing techniques, but the mechanical performance of 3D printed components depends strongly on printing parameters. This study investigates the effects of nozzle diameter on tensile strength, elastic modulus, and microstructure in 3D printed polylactic acid (PLA) specimens. Samples were fabricated using a range of nozzle sizes from 0.2mm to 0.5mm diameter and tested under uniaxial tensile loading until failure. The results show an increase in ultimate tensile strength and Young's modulus with increasing nozzle diameter. Scanning electron microscopy reveals enhanced interlayer adhesion for larger nozzle sizes, with a transition in fracture mode from interlayer to intralayer dominated. To further understand these findings, anisotropic constitutive models were developed to predict the mechanical properties of PLA. These models were derived using principles of composite laminate theory, which consider the effects of nozzle diameter on the material coherence between printed layers. The theoretical predictions made by these models were compared with the experimental data, showing a good agreement and providing deeper insight into the relationship between printing parameters and mechanical performance. The experimental and analytical results both highlight nozzle diameter as a critical factor determining achievable mechanical properties in FDM. This work provides insights into the key relationships between processing, structure, and properties, which can guide component design and process optimization in 3D printing of thermoplastic polymers.\u003c/p\u003e","manuscriptTitle":"Effect of Nozzle Diameter on Mechanical Properties and Microstructure of Fused Deposition Modeling 3D Printed Polylactic Acid Parts","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-26 12:33:31","doi":"10.21203/rs.3.rs-7953803/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7231c5af-bd58-4d53-9879-e0da8ad966b6","owner":[],"postedDate":"November 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-01-08T15:55:56+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-26 12:33:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7953803","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7953803","identity":"rs-7953803","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}