Five-axis material extrusion of high-performance structural parts with continuous carbon fiber-reinforced LM-PAEK

Five-axis material extrusion of high-performance structural parts with continuous carbon fiber-reinforced LM-PAEK | 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 Article Five-axis material extrusion of high-performance structural parts with continuous carbon fiber-reinforced LM-PAEK Nathaniel Heathman, Michael DeLay, Mehran Tehrani This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5412244/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 Additive manufacturing (AM) offers numerous advantages over standard manufacturing methods, such as design freedom and enabling limited production run components. Using continuous fiber-reinforced polymer composites, polymer AM can now produce end-use components with mechanical properties rivaling metals. In this paper, five-axis continuous fiber material extrusion (ME) is utilized to manufacture specimens from high-performance semi-crystalline low-melt polyaryletherketone™ (LM-PAEK™) composite. ASTM standardized testing showed record matrix-dominated and flexural properties for as-printed parts, with low porosity and high crystallinity. Annealing did not change mechanical properties or crystallinity. Additionally, steering radii specimens and a complex geometric bracket were manufactured using the full out-of-plane 3D printing capability of the five-axis equipment; subsequent X-ray computed tomography showed multiple manufacturing defects and voids when printing high-curvature rasters. Results thus pave the way for using LM-PAEK™ to replace other high-performance polymers in continuous fiber AM, although designers should take note of fiber steering in critical load-bearing structures. Physical sciences/Engineering/Aerospace engineering Physical sciences/Materials science/Structural materials/Composites Physical sciences/Materials science/Structural materials/Mechanical properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Material extrusion (ME), also known as fused filament fabrication (FFF) or Fused Deposition Modeling™ (FDM™), is an additive manufacturing (AM) technique that has been widely adopted and employed in recent years for a variety of applications, including prototyping, hobbyist parts, and, increasingly in recent years with advancements of material and process technologies, end-use components. ME brings several key advantages over conventional manufacturing techniques. First, ME allows the production of intricate geometries by optimizing designated paths (rasters or beads) and part geometry for specific loading situations, such as steering rasters around fastener holes. This can result in the production of parts with significantly higher specific performance but at a fraction of the weight and associated material costs. Second, ME can significantly reduce the amount of tooling (molds) required as compared to other conventional manufacturing techniques. If molds are still required during the ME process, they may be manufactured in-situ using relatively inexpensive materials. These molds (typically referred to as “supports” in AM) require little post finishing and can have reduced volume and complexity. In ME systems, a heated deposition nozzle (also called a hot end) attached to a positioning system is employed to melt and deposit the feedstock material, commonly a thermoplastic polymer, in rasters [ 1 ]. The rasters cool and solidify quickly after deposition to form layers, and the layers are deposited one on top of another to form a complete three-dimensional shape. ME printers can utilize either gantry-based positioning systems to deposit one 2-dimensional layer at a time at a given z-axis spacing, or robotic positioning systems to take advantage of placement in all three dimensions at once, called multi-axis or out-of-plane 3D printing [ 2 ]. The most common ME feedstock material is a thermoplastic polymer in the form of a filament with a circular cross section of a consistent diameter; however, certain equipment can also utilize thermoplastic pellets fed via a hopper [ 3 ]. Traditionally, low-cost low-strength commodity thermoplastics such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and nylon have been used to manufacture parts via ME. In recent years, high-performance thermoplastics, such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) from the polyaryletherketone (PAEK) family, or ULTEM™ 1010, a polyetherimide, are being increasingly used, enabling ME parts for end use in high-strength and high-temperature applications [ 4 ]. To push the boundaries of ME even further, fibers have been incorporated into feedstock filaments to print composite parts with superior fiber-direction mechanical properties and enhanced thermal properties as compared to their neat counterparts [ 5 ]. While short discontinuous fibers have been shown to increase the strength and stiffness of ME parts, a much larger advantage comes with utilizing continuous fibers [ 6 ]. The ME of continuous fiber reinforced polymers takes advantage of: a) fiber lengths that are much higher than the critical fiber length of the composite system, as well as b) higher fiber volume fractions, due to the packing of aligned fibers, to achieve specific mechanical properties that are approximately one to two orders of magnitude higher than those of their short fiber counterparts [ 7 ]. It must be noted that these mechanical properties are measured in the longitudinal fiber direction (i.e., fiber-dominated properties). A variety of polymer matrices and fibers can be used in the process; the former includes ABS, PLA, nylon, and the PAEK family of polymers, while the latter includes glass, Kevlar, and carbon fibers [ 8 ]. The emergence and widespread adoption of carbon fiber reinforced polymers (CFRPs) is one of the main developments in enabling ME technology for end-use components. With high strength and stiffness to weight ratios, these materials are directly applicable for use in high performance applications in the automotive, energy, and aerospace industries where high strength, low weight, and high temperature performance are required [ 9 ]. By combining CFRPs with AM technology, it becomes possible to leverage the benefits of AM processes to exploit the material advantages of CFRPs. However, when choosing to use continuous fibers rather than using short discontinuous fibers or neat feedstocks, a key change has to be made to the ME process involving the path planning for how the filaments are laid down during each layer. As opposed to short fiber or neat ME, the continuous fiber process must utilize a continuous path for each raster with a prescribed start and stop, due to the necessity to cut the filament at the end of each raster [ 10 – 12 ]. Typically, a minimum distance between start and stop is required due to machine limitations; each layer can have multiple rasters as long as this requirement is met. While this complication may seem detrimental, it in fact opens an opportunity to optimize the design of continuous fiber ME parts for particular loading situations in a way which increases specific strength and stiffness [ 9 , 13 , 14 ]. Additionally, the user must consider the manner in which continuous fibers are incorporated into the filament. There are two main methods: either using filaments that have been pre-impregnated with fibers via a melt impregnation process, or combining fibers and polymer together within the hot end immediately before printing [ 15 , 16 ]; care must be taken to ensure the proper wetting of fibers within the polymer [ 6 ]. The former method is used in this study. As with neat ME, the success of continuous fiber ME is highly dependent on processing parameters to develop ideal properties in the final part. Process speed, layer height and width, as well as nozzle, bed, and chamber temperatures are all critical parameters to the ME process, where each parameter has to be finely tuned for specific materials and printer types [ 17 , 18 ]. In the case of the manufacturing of high-performance amorphous and semi-crystalline polymers such as polyetherimide (PEI), polybenzimidazole (PBI), polyphenylene (PPS), and PAEKs, high nozzle, bed, and chamber temperatures along with slow speeds are typically required to consolidate the layers, and to achieve maximum crystallization if a semi-crystalline polymer is used [ 19 , 20 ]. Interlaminar bonding, degree of crystallinity, void development, and fiber misalignment and breakage are all significant mechanisms that contribute to the overall strength of parts manufactured via continuous fiber ME [ 21 ]. These mechanisms will now be discussed. Interlaminar bonding is the main factor governing the overall performance of continuous fiber ME parts, especially when subjected to loads that are not in the fiber direction [ 4 , 22 ]. This is a matrix-dominant property; in contrast, the performance of a printed part in the fiber direction is a fiber-dominant property that is unlikely to vary with different processing conditions [ 22 ]. Compared to thermoforming, where the polymer/fibers are heated uniformly to melting temperature under compressive forces and are then allowed to cool at a controlled rate, the ME process deposits molten material on top of an already cooled layer, relying largely on the heat in the extrudate to transfer to the previous layer [ 23 ]. The temperature in the previous layer thus heats up above glass transition temperature (T g ) and into the melt window where polymer can flow and its chains inter-diffuse across the interface to achieve bonding between the layers [ 4 , 24 ]. As such, the level of interlaminar bonding is highly dependent on the viscosity of the polymer and the time at which the two layers are in contact above T g . Generally, in ME processes, the cooling rates are very high (in the order of hundreds of K/s), which result in poor inter-diffusion and consequently poor interlaminar bonding. Bonding can, therefore, be significantly improved by the use of heated chambers and print beds, or, in certain cases, preheating the previous layer [ 18 , 25 , 26 ]. The degree of crystallinity must be considered when utilizing high-performance semi-crystalline polymers, such as those belonging to the PAEK family, as the crystallization process is significant to the overall part strength. Crystallinity in polymers refers to the self-organization of polymer chains into ordered groupings within the amorphous regions where polymer chains are disorganized. Crystalline regions provide significant improvements to overall strength, stiffness, increased toughness, and wear resistance when compared to their amorphous counterparts [ 27 ]. Primarily, crystallization occurs above T g as the part is cooled from melt when polymer chains organize into repeating units called lamella; these lamellae grow and align, forming spherulites or spherical groupings of crystalline polymer chains [ 28 ]. Crystallinity is highly dependent on cooling rate, as the ability of polymer chains to nucleate and grow spherulites is directly related to the time spent in the crystallization window [ 29 ]. This is of specific importance to the ME process due to the inherently high cooling rates observed during ME [ 30 ]; evidence shows high crystallinity is very difficult to achieve during the ME process. It should be noted that generally crystallinity is assumed to directly impede the inter-diffusion of polymer chains as previously described [ 31 ]. Another type of crystallization that can occur during the ME process is cold crystallization, where a material has its polymer chains regain mobility and begin to organize when temperature is held above the cold crystallization temperature (T cc ) [ 32 ]. To this end, manufacturers may recommend annealing of ME-printed parts, where the printed material is at first held at T g in the chamber to promote polymer inter-diffusion across layers, while at the same time having minimal crystallinity due to the high cooling rates from melt. Annealing is performed afterwards where the chamber temperature is further raised to T cc to promote crystal growth across layers. This high level of crystallinity therefore contributes to greater overall strength. A previous study by the authors on short carbon fiber-reinforced PEEK and PEKK found that the high level of degree of crystallinity of the former impeded the inter-diffusion of polymer chains across layer boundaries, resulting in a low interlaminar tensile strength of < 20 MPa. The latter’s lower degree of crystallinity immediately after printing allowed for greater polymer chain inter-diffusion; the crystallinity increased only upon post-annealing, resulting in an improved interlaminar tensile strength of ~ 50 MPa. For comparison, the longitudinal tensile strength of either composite material is ~ 100 MPa. Void development in CRFPs manufactured via ME can significantly impact mechanical properties [ 33 ]. The appearance of voids is inherent to the ME process due to the stacking of the extruded beads of an elliptical shape that creates diamond-shaped or triangular voids at each raster boundary [ 34 ]. Furthermore, in the ME of fiber reinforced polymers, voids may already be present within the feedstock filament itself and can be passed onto the part [ 22 , 35 ]; these voids appear in the filament due to a low polymer matrix-fiber adhesion, or inability to fully impregnate the fibers with polymer [ 36 ]. Voids will therefore lower interlaminar properties due to stress concentrations and the reduction of effective cross-sectional area [ 4 , 22 ]. Successful attempts to eliminate voids in ME parts have been made using several different methods. In one study, a significant reduction of inter-raster voids in a neat polymer was made by increasing the extrusion rate (amount of material deposited) to increase the inter-raster pressures allowing the molten material to flow and fill these areas [ 26 , 37 ]. Another method proposed for void reduction is utilizing a heated compaction roller that follows the hot end to compress the rasters, thereby decreasing the void content [ 38 ]. Hot isostatic pressing (HIP) has also been utilized, where an ME-manufactured part is subjected to elevated temperatures and isostatic pressures in a post processing step to remove voids and increase interlayer bonding [ 39 ]. The latter methods may also give the side benefit of increasing interlaminar intimate contact. Minimizing fiber misalignment and breakage during the ME of continuous fiber filaments presents a particular challenge [ 40 , 41 ]. During printing, fibers are aligned in the direction of travel of the print head. Due to the fixed orientation of the deposition nozzle, fibers resist a change in direction during the print, which can lead to twists, overlaps, and void formation between fibers any time the print direction is altered. In a study using polyamide 6 − 1 continuous carbon fiber filaments, samples were prepared at various radii and angles to inspect the behavior of the fibers under different curvatures [ 41 ]. While fibers are well aligned with minimal voids at high radii, print defects occurred at smaller radii, including path errors, fiber twisting, folding, and misalignment, along with the formation of voids. Considering these defects are inherent with the process, it is important to note their occurrence and be able to adjust raster paths to mitigate their occurrence, ensuring the highest strength possible in the manufactured parts. The mechanisms of interlaminar bonding, degree of crystallinity, void development, and fiber misalignment and breakage have now been discussed for their overall contribution to mechanical properties in parts manufactured via continuous fiber ME. With the development of off-the-shelf printers using continuous fiber filaments by a variety of manufacturers such as Markforged, 9T Labs, Desktop Metal, Anisoprint, Arevo, and others, mechanical properties are beginning to be well documented specifically for lower grade materials [ 42 – 46 ]. However, much less research has been conducted on semicrystalline high-performance thermoplastics. In one study, van de Werken et al. sought to investigate the mechanical and thermal properties and microstructure of ME parts using AS4C continuous carbon fiber PEEK filaments with a 42% fiber volume fraction (v f ), both in as-printed form as well as after a HIP post processing procedure [ 39 ]. Results show as-printed samples achieved a short beam strength (SBS) of 27 MPa, flexural strength of 834 MPa, a void content of 10%, and a degree of crystallinity of 22%. When subjected to HIP at 200 psi and 250 ˚C, SBS was increased to 35 MPa and flexural strength to 1221 MPa, with the void content decreased to 5% and the degree of crystallinity increasing slightly to 23%. Kuba et al. studied the effect of melt viscosity on void content and interlaminar tensile strength of specimens manufactured from three different grades of PEEK using continuous fiber ME [ 47 ]. Tests revealed that the lower melt viscosity filament halved the void content and more than doubled the interlaminar tensile strength when compared to the standard viscosity material, providing significant evidence that reducing melt viscosity in semi-crystalline materials helps improve bonding strength and reducing void content. Meng et al. employed a laser preheating technique in the continuous fiber ME process to enhance interlaminar bonding and tested its effectiveness by manufacturing and testing two viscosity grades of PEEK in a 38 wt.% carbon fiber filament [ 18 ]. With laser preheating enabled, a maximum short beam strength, flexural strength, and flexural modulus of 36 MPa, 480 MPa, and 37 GPa, respectively, were achieved. While these studies show a variation in flexural strength and void content, the low short beam strength values remain consistent, with the conclusion that PEEK suffered from too high of a melt viscosity to enable sufficient polymer flow, polymer chain mobility and interfacial diffusion for maximizing interlaminar bonding in the continuous fiber ME process. An alternate suggestion was made that premature crystallization occurred prior to polymer interdiffusion across interfaces, which minimized intimate contact and consequently lowered short beam strength. It should be noted that the aforementioned examples used modified gantry-based 3D printers; the authors were unable to find studies on the ME of continuous fiber-reinforced semicrystalline high-performance thermoplastic composite materials using a multi-axis 3D printer. This paper aims to utilize a new high-performance semi-crystalline material from the PAEK family, denoted as low-melt PAEK (LM-PAEK™), to manufacture specimens using a commercially available multi-axis 3D printer and analyze their thermal, microstructural, and mechanical properties. LM-PAEK, while providing similar strength, high temperature performance, chemical and wear resistance to PEEK, offers a lower melting temperature and viscosity, which in turn should help to alleviate the interlaminar bonding challenges as seen in previous research of continuous fiber ME of PEEK. Samples were manufactured with and without an annealing post process step, and the resultant ASTM standardized properties of both sets of samples were compared. Further custom specimens were manufactured to understand the effects of steering radii and the utilization of the out-of-plane axis on void content. The results provide an understanding into the properties achieved with this new material in the continuous fiber ME process and can drive advancement of continuous fiber-reinforced ME beyond previous insights developed with lower grade materials or with gantry-based systems. 2. Results 2.1 Thermal and microstructural characterization DSC was first performed on the feedstock filament. Figure 1 a shows DSC curves for the filament in three forms: as delivered, heated to melt and cooled at 500 K/min (denoted as fast cooled), and heated to melt and cooled at 1 K/min (denoted as slow cooled). The as-delivered filament showed a 7% crystallinity, a 5% minimum with fast cooling, and a 25% maximum with slow cooling. These values are typical of carbon fiber LM-PAEK [ 48 , 49 ]. All samples exhibited a T g of ~ 150°C. Slow-cooled samples demonstrated a slightly higher melting peak compared to the other two samples. All samples melted below the processing nozzle temperature of 340°C used here. DSC was then performed on selected portions of the SBS and CBS samples to inspect the development of crystallinity during the manufacturing process. In ME, the cooling rate from the melt is expected to be rapid (in the order of hundreds of Kelvins per second) [ 39 , 50 ]. The use of a heated bed at 200°C, as employed in this study, may enable cold crystallization to occur within relatively short samples. However, taller samples are expected to cool at similar rates but may not remain near 200°C, and hence may not achieve a large degree of cold crystallization. Degree of crystallization values as measured from several locations in different specimens are summarized in Table 1 . SBS samples, with DSC curves provided in Fig. 1 b, showed a near maximum crystallinity of ~ 24% developed at the bottom and middle of the sample, but crystallinity was only 7% at the top surface of the sample. The annealed samples on the other hand had a consistent crystallinity of ~ 24% through the entire height of the sample. Given that the SBS samples were 6 mm tall, the effects of the heated print bed were only noticeable within a few millimeters, which helped the deposited rasters to crystallize by sustaining their temperatures for sufficient durations within the cold-crystallization window. Regardless, the annealing procedure resulted in near maximum crystallinity values throughout the z-height of all samples, and should therefore be recommended for samples taller than 3 mm. The procedure may eliminate residual stresses and is not expected to result in sample deformations. Table 1 Crystallinity values for different samples at multiple locations. Sample and location Crystallinity (%) SBS sample, as-printed 6 mm from print bed (top) 7 3 mm (middle) 24 0 mm (bottom) 24 SBS sample, annealed 6 mm (top) 24 0 mm (bottom) 24 CBS sample 25 mm (top) 11 12.5 mm (middle) 11 0 mm (bottom) 20 The height-dependent difference in crystallinity was also shown in the CBS samples (printed on their side), which had a relatively high crystallinity at the bottom but had a lower crystallinity of ~ 11% at the middle and top of the sample, 12.5 mm and 25 mm from the print bed, respectively. Results are given in Table 1 . An interesting phenomenon in the SBS sample DSC curves, as in Fig. 1 b, is the double melting curve. Previous research has shown that this is a result of isothermal holds above glass transition temperature where there is a primary crystallization process where spherulitic entities are formed, and a secondary process, where interlamellar crystalline structures grow [ 28 ]. The double melting curves appeared in the DSC curves at approximately 10 to 30 ˚C above the isothermal hold temperatures (200 ˚C for the as-printed parts and 210 ˚C for the annealed parts) [ 28 ]. µCT was conducted on an as-printed SBS coupon. A tomograph of an as-printed SBS coupon is shown in Fig. 2 a. A 1.63% void volume content was measured by analyzing the µCT slices; voids were predominantly located at filament interfaces and travel longitudinally along the interfaces for long distances within the sample. These voids were segmented during µCT analysis from the sample and reconstructed in three dimensions to demonstrate how they are located within the sample, as shown in Fig. 2 b. As previously found for neat thermoplastic ME parts [ 37 ], diamond shaped voids are expected to form between individual rasters due to the oval shape of the deposited filaments. However, in the continuous fiber ME process studied here, voids appeared at random predominantly on the raster boundaries, with a small portion of voids appearing within the rasters themselves. This suggests that voids appeared at interfaces due to incomplete intimate contact (lack of flow and interdiffusion), which was in turn caused by a lack of pressure to facilitate polymer flow, whereas the voids within the rasters could be from the feedstock filament. The measured void content in this study is significantly lower compared to previous literature on continuous fiber-PEEK ME parts, 10% in one study and 8% in another [ 39 , 47 ]. Considering the similar manner of fabrication for the aforementioned PEEK specimens, the lower void content presented here suggests that the lower viscosity at melt for LM-PAEK was the driving factor for the low void content. It should be noted that while the void content is low, the voids are elongated and present at most raster-raster and layer-layer interfaces, which may reduce the interlaminar shear strength. Up to this point, full thermal and microstructural analyses for the samples with and without post processing have been presented. These will in turn affect and explain the mechanical properties as described in the next section. 2.2 ASTM standardized mechanical property characterization and fractography Results for all mechanical tests are shown in Table 2 and representative loading curves are shown in Fig. 3 . Analyses of the mechanical testing results show multiple interesting phenomena and are presented alongside fractography in Fig. 4 and SEM imaging in Fig. 5 . Table 2 Mechanical property results. Property Value Flexural test, as-printed Strength (MPa) 943 ± 24 Maximum strain (%) 1.1 ± 0.0 Chord modulus (GPa) 84 ± 1 Flexural test, annealed Strength (MPa) 930 ± 44 Maximum strain (%) 1.2 ± 0.1 Chord modulus (GPa) 86 ± 2 Short beam strength, as-printed SBS (MPa) 60 ± 3 Short beam strength, annealed SBS (MPa) 60 ± 3 Curved beam strength CBS (MPa) 62 ± 7 Flexural testing is a common test to assess intra-laminar properties of composites, and flexural failure is typically fiber compression under a mixed stress mode. A mean flexural strength of 943 MPa was achieved for the as-printed coupons, which is higher than any as-printed result found in previous studies [ 39 ]. Flexural modulus was 84 GPa, which is expected following the rule of mixtures: 37% fiber volume fraction and standard modulus carbon fibers (modulus of 230 GPa). Annealing flexural coupons did not change the mechanical properties outside the error bounds. Given the small height of the coupons (4 mm), all parts of the printed coupons are expected to benefit from the proximity to the heated print bed and achieve a near maximum crystallinity of ~ 24% measured for the bottom half of the SBS coupon (see Table 1 ). Interlaminar properties are therefore expected to remain the same during annealing. Fractography was performed to investigate failure modes as in Fig. 4 . The flexural samples showed a typical fracture surface with clearly defined tensile and compression stress states as shown in Fig. 4 a where a sharp jagged fracture surface is indicative of tensile failure and a smooth flat fracture surface is indicative of compression loading. No delamination was observed in flexural samples as is expected for the span-to-thickness ratio. SEM imaging of the flexural samples was conducted as per Fig. 5 to inspect the fiber-matrix interfaces on fracture surfaces. Figure 5 a shows a magnified area of the flexural sample under tensile stress. Analysis of this region shows multiple fibers bundled together with polymer matrix, a small number of individual fibers pulled out of the bundles, and overall, very few clean fibers. Overall, inspection of the fracture surface via SEM imaging shows significant evidence of a strong fiber-matrix interphase region, which can also be expected to contribute to various other mechanical properties not tested in the flexural tests such as interlaminar shear strength or transverse tensile strength. The SBS test is similar to the flexural test, except that given the change to the span-to-thickness ratio, failure is expected to occur via interlaminar shear rather than intra-laminar tensile and/or compressive failure. The 60 MPa as-printed SBS strengths achieved here is significantly higher than the maximum SBS values of ~ 35 MPa found in other studies of continuous fiber PEEK ME parts [ 18 , 39 ]. However, these as-printed strength values are only ~ 60% of compression molded LM-PAEK parts, with a manufacturer-reported SBS strength ~ 95 MPa [ 51 ]. While these SBS values still fall short of those for compression molded samples, 60 MPa is considered relatively high for a part manufactured via ME where intimate contact and interdiffusion between layers suffer due to high cooling rates and dissimilar layer temperatures during deposition, although intimate contact and interdiffusion is expected to improve due to the proximity to the heated print bed. Annealing did not affect the SBS results, as shear failure occurred predominantly in the middle region of the coupon, which had the same degree of crystallinity with or without annealing as reported in Table 1 . Figure 4 b shows a side profile an as-printed SBS sample after testing. The observed failure mode for all as-printed and annealed SBS samples is inelastic deformation with a small amount of crushing under the loading roller. This failure mode is representative of a large amount of plastic deformation without apparent delamination on the coupon edges. Inspection of the loading curves in Fig. 3 a shows clear plastic deformation and no sharp drop-offs in loading indicative of delamination. SBS failure behavior presented here is different than traditional samples manufactured by hand lay-ups or automated fiber placement where significant shear failure and delamination occurs, evident by the appearance of a few cracks near the middle of the sample [ 52 ]. The presence of several smaller cracks at interlaminar regions, Fig. 2 a-b, could be the reason for the gradual (several smaller and internal shear delaminations) failure behavior in ME samples as compared to sudden failure in samples manufactured by other methods. Given the inelastic deformation failure of the SBS samples, a crack was initiated at the end of the sample with a razor blade and split manually in order to image the interfaces under SEM to inspect the fiber-matrix interfaces. This fracture surface is shown in Fig. 5 b, where the most notable feature is the remnant of the polymer matrix on the fibers. Combined with the insights from the flexural coupon in Fig. 5 a, overall SEM fractography shows significant evidence of a strong fiber-matrix interphase region which is expected to improve matrix-dominated transverse and through-thickness (interlaminar) direction properties. The CBS testing method typically induces an out-of-plane tensile stress within the curved region of the specimen, specifically through its thickness if manufactured on a curved mold. However, in order to investigate the transverse-direction properties, the sample was printed on its side; in this case, the measured tensile strength would be in the inter-raster transverse direction. CBS testing results show the resultant maximum inter-raster tensile strength of 62 MPa. However, upon inspection of the fractured coupon, not only does the in-plane fracture surface in Fig. 4 c show clear tensile stress induced fractures in between rasters as expected, but the out of plane surface shown in Fig. 4 d also shows delamination and buckling between layers. While the latter phenomenon is unexplained in the context of the ASTM standard, it can be theorized that the delamination is: a) a result of complex 3D stresses arising from fiber misalignments in the 6.4 mm radius bend during manufacturing (note that all previous coupons did not have curved rasters), and/or b) variations in local matrix properties caused by crystallinity changes throughout the 25 mm tall sample contributed to the delamination; the CBS sample was not post-annealed, and therefore achieved a low crystallinity in the regions far away from the bed that are shown as failed in Fig. 4 d. Further µCT characterization is discussed in the next section to explain these anomalous fracture patterns. 2.3 µCT characterization of steering radii specimens and CBS sample Steering is recognized for its tendency to cause fiber misalignments, although current understanding of this process remains limited even as steering is commonly employed in ME. The observed failure behavior in the CBS test underscores the importance of gaining further insight into the steering process. To this end, the CBS sample was scanned, and a tomograph is shown in Fig. 6 . Furthermore, steering radii specimens were manufactured and then scanned with µCT, and their reconstructions are also shown in Fig. 6 . Figure 6 a shows the tomographic image of a printed filament (one single raster) at a radius of 1.25 mm, the minimum printable with the Mantis Composites machine, where the fiber path was steered to align directly next to the previous path. It is clear that the fibers folded over one another to round the corner as opposed to being steered. As the radius decreased from 1000 mm to 1.25 mm, as in Fig. 6 f through Fig. 6 a, fibers tended to be unable to conform to the steering angle and tended to fold over, wrinkle, and twist as opposed to following the programmed path. This trend was even more evident in the interior of the curved regions, where the radius is smaller than the exterior. This phenomenon can be explained by the different forces experienced in the individual filaments during deposition: the interior of the curve would be under compression, where the exterior portion would be under tension [ 41 ]. The compressive forces caused fibers to buckle whereas the tensile forces caused the fibers to fold over one another. Additionally, voids may be introduced in the twisted regions, as evidenced in Fig. 6 e and in the CBS sample as in Fig. 6 g, and might have acted as stress concentrations. As such, the combination of fiber wrinkling and folding, interlaminar and intra-laminar voids, and stress concentrations might have resulted in the failure modes and cracks as previously detailed in CBS fractography. One possible solution to this issue is the development of a rotating deposition nozzle that manually twists the filament during deposition in corners to relieve these stresses [ 53 ]. Alternatively, compression molding may succeed in closing up these intralaminar voids. 2.4 Manufacturing and µCT characterization of geometric bracket To highlight the out-of-plane printing capability of the continuous fiber ME process in the machine developed by Mantis Composites, a complex 3-dimensional geometric bracket was manufactured and analyzed for overall quality. Figure 7a-b show the nozzle path and orientation for the bracket shown in Fig. 7c. The geometric bracket was printed on a heated metal mold, following a path that formed a single continuous loop. The orientation of the nozzle was maintained perpendicular to the mold’s surface. Processing parameters such as speed and temperature were varied depending on the location in the path to optimize the part quality. Given the varying process parameters and nozzle travel orientation during the print, part properties may vary from one location to the next. It is critical to analyze and note any variations in quality. The geometric bracket was imaged with µCT in two regions of importance to view void development and defects. Figure 8 a provides an image of the bracket, with boxes highlighting the two areas (named “corner” and “slope”) that were scanned. Figure 8 b shows a cross-sectional tomograph of the former corner region. In this region, the amount of voids was increased where the fibers were steered around the corner when compared to the straighter regions. Figure 8 c provides an image of the corner area with the voids reconstructed and represented in green. A void analysis of the steered section yields an 8.8% void content in the steered area, compared to 5.2% when the fibers were oriented in a straight line; for comparison, note that the SBS coupons contained < 2% voids. These results validate the previous evidence of an increased void content in regions of higher curvature. Figure 8 d-e provide cross sectional tomographs of the slope region. Notable findings include the large presence of voids in this region, concentrated at the bottom of the sample where fibers were placed on the mold. Void analysis of the entire slope section yielded a 5% void content. However, when looking at Fig. 8 e, the difference in void content between the left and the right of the slope region can be seen. Note that in the left region the filament was deposited in travelling down the slope, compared to the right region where the filament was deposited traveling up the slope. The red box located in Fig. 8 e highlights an area with a significantly large void volume content; this defect occurred in the area where filament was travelling down the slope. It can be theorized that while the nozzle travels down an incline, as in the left side, the direction of travel corresponding to mold angle causes a natural lifting effect on the deposited filament, producing an increased void content or large defects. Results from µCT analysis of this geometric bracket offer valuable insights into the quality of complex parts produced via continuous fiber ME. Designers therefore need to consider all aspects of the filament path and travel orientation to minimize the occurrence of defects in a part. 3. Discussion In this study, various ASTM standardized and custom complex-shaped specimens were fabricated using continuous fiber material extrusion (ME), also known as fused filament fabrication (FFF), and a newly developed semi-crystalline high-performance thermoplastic called LM-PAEK™. Analysis of the samples' mechanical properties, thermal properties, and microstructure revealed that LM-PAEK is well-suited for ME and outperforms other high-performance polymers in terms of part quality and performance. Mechanical testing demonstrated exceptional interlaminar shear strength (via short beam strength) and flexural strength of 60 MPa and 943 MPa, respectively, for the as-printed coupons. These samples also exhibited an inter-raster tensile strength (via a modified version of the curved beam strength test) of 62 MPa. As an indirect comparison, short carbon fiber-reinforced polyetheretherketone (PEEK) parts had a recorded < 20 MPa interlaminar tensile strength in a previous study by the authors [ 22 ]. Void analysis of a printed flat coupon revealed a void volume content of 1.6%, primarily concentrated along raster interfaces. Crystallinity assessment via differential scanning calorimetry (DSC) indicated that the filament was delivered with 7% crystallinity, as compared to a maximum crystallinity of 25% achieved through slow cooling from melt. DSC testing of the samples themselves demonstrated near-maximum crystallinity at the bottom of the sample, close to the heated bed; crystallinity decreased with increasing height off the print bed. It was demonstrated that near-full crystallization of a part could be achieved through a relatively low-temperature (210 ˚C) and quick post-annealing step, with no change in the tested mechanical properties; the increased crystallization is expected to improve creep and chemical resistance properties. Analysis of micro-computed tomography (µCT) data obtained from single deposited filaments (“steering radii specimens”) showed significant buckling, twisting, and folding of fibers when steered around sharp corners. These defects resulted in the formation of large voids in parts with curved shapes where the filaments had to conform. Additionally, a complex geometric bracket was successfully manufactured, thereby demonstrating the viability of out-of-plane continuous fiber ME; voids similarly appeared in regions of high curvature, but also tended to appear when the nozzle travels downwards an inclined mold according to the lifting effect. The presented results highlight the ability to manufacture intricate parts with continuous fiber LM-PAEK via five-axis ME with enhanced interlaminar bonding and reduced void content compared to their PEEK counterparts. It can be theorized that the lower processing temperature and viscosity provided by LM-PAEK significantly aid in the interlaminar bonding process. Based on the findings of this study, LM-PAEK should be considered the new standard for use in continuous fiber ME of high-performance semi-crystalline polymers, and further study should be directed to the elucidation of void growth at different mold angles whenever a five-axis 3D printer is used. 4. Methods 4.1 Materials The material used for sample fabrication is carbon fiber LM-PAEK™ continuous fiber filament. The filament comprises AS4C carbon fiber and Victrex AE250 LM-PAEK™ polymer. with a resulting 37% carbon fiber volume fraction (as measured via micro computed tomography of the filament) and a 0.8 mm filament diameter. LM-PAEK is a high performance semi-crystalline polymer that belongs to the PAEK group of thermoplastics and is thus similar to PEEK and PEKK. LM-PAEK has comparable mechanical properties and high chemical resistance, but provides a lower processing temperature due to a reorganization of the polymer chains into co-polymer groupings; given a melting temperature measured at 307 ˚C, its processing temperature is brought down ~ 60 ˚C as compared to PEEK and PEKK [ 54 ]. 4.2 Fabrication of ASTM standard samples All samples were fabricated with a 5-axis continuous fiber material extrusion (ME) printer developed by Mantis Composites. A nozzle speed of 10 mm/s, extruder temperature of 340 ˚C, and bed temperature of 200 ˚C were utilized; the nozzle speed was half the speed of gantry-based PEEK or PEKK nozzle speeds as found in literature [ 22 , 47 ]. Three types of samples were fabricated per ASTM standards for analysis: ASTM D2344 for short beam strength (SBS), ASTM D6415 for curved beam strength (CBS), and ASTM D7264 for flexural properties. SBS and flexural samples were fabricated oversize and machined to the correct sizes afterwards; owing to the bend in the shape and the difficulty in machining, CBS samples were manufactured to size on their side. After fabrication, half the SBS and flexural samples were subjected to annealing for comparison to non-annealed (as-printed) coupons; annealing consisted of heating samples from room temperature to 160 ˚C at a 3 ˚C/min rate, holding for 30 minutes, then heating from 160 ˚C to 210 ˚C at a 3 ˚C/min rate, followed again by holding for 1 hour, after which they were allowed to cool to room temperature in the oven at an uncontrolled rate. Samples were then characterized as described in a later section. 4.3 Fabrication of custom specimens Following the ASTM standardized mechanical testing, the phenomena of fiber misalignment and fiber breakage in high-curvature turns were assessed via printing specimens of varying steering radii at a single layer height (“steering radii specimens”), with radii varying between 1.25 mm and 100 mm. Specimens were then characterized as described in a later section. Additionally, a complex 3-dimensional geometric bracket was manufactured fully utilizing the 5-axis capability of the printer, and then analyzed for defects and voids as described in a later section. Path planning was optimized to ensure that a constant fiber direction was maintained along the path of the geometric bracket. 4.4 Characterization techniques Thermal properties were evaluated via differential scanning calorimetry (DSC) to determine the crystallinity of the samples. DSC tests were carried out in multiple regions within each sample to form an understanding of how crystallinity developed during the printing process. A heating rate of 10 K/min was used for all DSC tests. Cross-sectional microscopy and micro computed tomography (µCT) were performed with a MicroXCT 400 Zeiss machine to analyze the microstructure of the filament and printed samples for fiber distribution, defects, and void content. Additionally, the steering radii specimens and geometric bracket were scanned with µCT to analyze fiber breakage and twisting as well as void development. The ImageJ and Dragonfly software were used for image analysis. ASTM standardized mechanical property characterization was carried out for short beam strength (SBS), curved beam strength (CBS), and flexural strength and modulus. SBS is a qualitative measure of interlaminar shear strength (ILSS) and is commonly used to assess bonding (consolidation) degree in additively manufactured composites. The CBS testing procedure utilizes a curved beam specimen comprised of two straight legs joined by a 90° bend with an inner radius of 6.4 mm; when a force is applied through a 4-point loading fixture, it induces an out-of-plane tensile stress within the curved region of the specimen through its thickness, and so the test is considered to be an assessment of interlaminar tensile strength (ILTS) through the thickness. Flexural testing is another common test to assess intra-laminar properties of composites [ 55 ], and the failure of flexural coupons is typically fiber compression under a mixed stress mode. Figure 9 provides illustrations of all ASTM tests carried out. Further fractography of the tested coupons was conducted using optical microscopy using a Nikon D7000 camera with a 105 Sigma EX macro lens and scanning electron microscopy (SEM) using a FEI Quanta 650 ESEM machine. Samples were sputtered with a few nanometers layer of gold prior to SEM. Declarations Competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contribution NH: writing, validation, methodology, investigation, formal analysis, data curation. MD: methodology, manufacturing, funding acquisition, conceptualization. MT: methodology, draft review and editing, formal analysis, data curation, advising, funding acquisition, conceptualization. Acknowledgements The authors are grateful for the research support provided by the Air Force Research Laboratory (AFRL) award no. FA8649-21-P-0122 and the Air Force Office of Scientific Research (AFOSR) award no. FA9550-21-1-0066. Data availability The corresponding author will make the data supporting this paper available upon reasonable request. References Tran, T.Q., Ng, F.L., Kai, J.T.Y., Feih, S., Nai, M.L.S. Tensile Strength Enhancement of Fused Filament Fabrication Printed Parts: A Review of Process Improvement Approaches and Respective Impact. Additive Manufacturing 54, 102724 (2022). Badarinath, R., Prabhu, V. Integration and evaluation of robotic fused filament fabrication system. Additive Manufacturing 41, 101951 (2021). Ferreira, I., Machado, M., Alves, F., Torres Marques, A. A review on fibre reinforced composite printing via FFF. Rapid Prototyping Journal 25(6), 972–988 (2019). Gao, X., Qi, S., Kuang, X., Su, Y., Li, J., Wang, D. Fused filament fabrication of polymer materials: A review of interlayer bond. Additive Manufacturing 37, 101658 (2021). Brenken, B., Barocio, E., Favaloro, A., Kunc, V., Pipes, R.B. Fused filament fabrication of fiber-reinforced polymers: A review. Additive Manufacturing 21, 1–16 (2018). Pandelidi, C., Bateman, S., Piegert, S., Hoehner, R., Kelbassa, I., Brandt, M. The technology of continuous fibre-reinforced polymers: a review on extrusion additive manufacturing methods. The International Journal of Advanced Manufacturing Technology 113(11), 3057–3077 (2021). van de Werken, N., Tekinalp, H., Khanbolouki, P., Ozcan, S., Williams, A., Tehrani, M., Additively manufactured carbon fiber-reinforced composites: State of the art and perspective. Additive Manufacturing 31, 100962 (2020). Zhuo, P., Li, S., Ashcroft, I.A., Jones, A.I. Material extrusion additive manufacturing of continuous fibre reinforced polymer matrix composites: A review and outlook. Composites Part B: Engineering 224, 109143 (2021). Fernandes, R.R., van de Werken, N., Koirala, P., Yap, T., Tamijani, A.Y., Tehrani, M. Experimental investigation of additively manufactured continuous fiber reinforced composite parts with optimized topology and fiber paths, Additive Manufacturing 44, 102056 (2021). Suzuki, T., Fukushige, S., Tsunori, M. Load path visualization and fiber trajectory optimization for additive manufacturing of composites. Additive Manufacturing 31, 100942 (2020). Yamamoto, K., Luces, J.V.S., Shirasu, K., Hoshikawa, Y., Okabe, T., Hirata, Y. A novel single-stroke path planning algorithm for 3D printers using continuous carbon fiber reinforced thermoplastics. Additive Manufacturing 55, 102816 (2022). Yap, T., Tamijani, A.Y., Tehrani, M. Optimum Conversion of Design Optimized Fiber Paths to 3D Printable G-Codes. 37th Technical Conference of the American Society for Composites, ASC 2022, DEStech Publications Inc., 2022. van de Werken, N., Hurley, J., Khanbolouki, P., Sarvestani, A.N., Tamijani, A.Y., Tehrani, M. Design considerations and modeling of fiber reinforced 3D printed parts. Composites Part B: Engineering 160, 684–692 (2019). Yap, T., He, Z., Wang, Z., Tamijani, A.Y., Tehrani, M. Experimental investigation and validation of strength-based topology and fiber path optimization in additively manufactured continuous fiber reinforced composites. Additive Manufacturing 89, 104274 (2024). Struzziero, G., Barbezat, M., Skordos, A.A. Consolidation of continuous fibre reinforced composites in additive processes: A review. Additive Manufacturing 48, 102458 (2021). Uşun, A., Gümrük, R. The mechanical performance of the 3D printed composites produced with continuous carbon fiber reinforced filaments obtained via melt impregnation. Additive Manufacturing 46, 102112 (2021). Li, J., Durandet, Y., Huang, X., Sun, G., Ruan, D. Additively manufactured fiber-reinforced composites: A review of mechanical behavior and opportunities. Journal of Materials Science & Technology 119, 219–244 (2022). Luo, M., Tian, X., Shang, J., Zhu, W., Li, D., Qin, Y. Impregnation and interlayer bonding behaviours of 3D-printed continuous carbon-fiber-reinforced poly-ether-ether-ketone composites. Composites Part A: Applied Science and Manufacturing 121, 130–138 (2019). Pu, J., McIlroy, C., Jones, A., Ashcroft, I. Understanding mechanical properties in fused filament fabrication of polyether ether ketone. Additive Manufacturing 37, 101673 (2021). Wu, H., Sulkis, M., Driver, J., Saade-Castillo, A., Thompson, A., Koo, J.H. Multi-functional ULTEM™1010 composite filaments for additive manufacturing using Fused Filament Fabrication (FFF). Additive Manufacturing 24, 298–306 (2018). Kabir, S.M.F., Mathur, K., Seyam, A.-F.M. A critical review on 3D printed continuous fiber-reinforced composites: History, mechanism, materials and properties. Composite Structures 232, 111476 (2020). Yap, T., Heathman, N., Phillips, T., Beaman, J., Tehrani, M. Additive Manufacturing of Polyaryletherketone (PAEK) polymers and their composites. Composites Part B: Engineering 266, 111019 (2023). Blok, L.G., Longana, M.L., Yu, H., Woods, B.K.S. An investigation into 3D printing of fibre reinforced thermoplastic composites. Additive Manufacturing 22, 176–186 (2018). Iragi, M., Pascual-González, C., Esnaola, A., Lopes, C.S., Aretxabaleta, L. Ply and interlaminar behaviours of 3D printed continuous carbon fibre-reinforced thermoplastic laminates; effects of processing conditions and microstructure. Additive Manufacturing 30, 100884 (2019). Heathman, N., Yap, T., Tehrani, M. Hot Isostatic Pressing to Enhance Inter-Laminar Tensile Strength in Additively Manufactured Carbon Fiber-PEEK Parts. 37th Technical Conference of the American Society for Composites, ASC 2020, DEStech Publications Inc., 2020. Martinez, J., Yap, T., Tehrani, M. Effects of Extrusion Rate and Post-Annealing on Mechanical Properties and Printing Quality of Additively Manufactured Carbon Fiber Reinforced Polyetherketoneketone (PEKK) Parts, 37th Technical Conference of the American Society for Composites, ASC 2022, DEStech Publications Inc., 2022. Vaes, D., Van Puyvelde, P. Semi-crystalline feedstock for filament-based 3D printing of polymers. Progress in Polymer Science 118, 101411 (2021). Pérez-Martín, H., Mackenzie, P., Baidak, A., Ó Brádaigh, C.M., Ray, D. Crystallinity studies of PEKK and carbon fibre/PEKK composites: A review. Composites Part B: Engineering 223, 109127 (2021). Yi, N., Davies, R., Chaplin, A., McCutchion, P., Ghita, O. Slow and fast crystallising poly aryl ether ketones (PAEKs) in 3D printing: Crystallisation kinetics, morphology, and mechanical properties. Additive Manufacturing 39, 101843 (2021). Gao, S.-L., Kim, J.-K. Cooling rate influences in carbon fibre/PEEK composites. Part 1. Crystallinity and interface adhesion. Composites Part A: Applied Science and Manufacturing 31(6), 517–530 (2000). Adhikari, S., Durning, C.J., Fish, J., Simon, J.-W., Kumar, S.K. Modeling Thermal Welding of Semicrystalline Polymers. Macromolecules 55(5), 1719–1725 (2022). Choupin, T., Fayolle, B., Régnier, G., Paris, C., Cinquin, J., Brulé, B. Isothermal crystallization kinetic modeling of poly(etherketoneketone) (PEKK) copolymer. Polymer 111, 73–82 (2017). de Macedo, R.Q., Ferreira, R.T.L., Gleadall, A., Ashcroft, I. VOLCO-X: Numerical simulation of material distribution and voids in extrusion additive manufacturing. Additive Manufacturing 40, 101900 (2021). Tao, Y., Kong, F., Li, Z., Zhang, J., Zhao, X., Yin, Q., Xing, D., Li, P. A review on voids of 3D printed parts by fused filament fabrication. Journal of Materials Research and Technology 15, 4860–4879 (2021). Polyzos, E., Ravindranath, S.B., Hemelrijck, D.V., Pyl, L. Analytical and numerical modeling of voids in additively manufactured thermoplastic parts. Additive Manufacturing 48, 102356 (2021). Yang, D., Zhang, H., Wu, J., McCarthy, E.D. Fibre flow and void formation in 3D printing of short-fibre reinforced thermoplastic composites: An experimental benchmark exercise. Additive Manufacturing 37, 101686 (2021). Ghorbani, J., Koirala, P., Shen, Y.-L., Tehrani, M. Eliminating voids and reducing mechanical anisotropy in fused filament fabrication parts by adjusting the filament extrusion rate. Journal of Manufacturing Processes 80, 651–658 (2022). Ueda, M., Kishimoto, S., Yamawaki, M., Matsuzaki, R., Todoroki, A., Hirano, Y., Le Duigou, A. 3D compaction printing of a continuous carbon fiber reinforced thermoplastic. Composites Part A: Applied Science and Manufacturing 137, 105985 (2020). van de Werken, N., Koirala, P., Ghorbani, J., Doyle, D., Tehrani, M. Investigating the hot isostatic pressing of an additively manufactured continuous carbon fiber reinforced PEEK composite. Additive Manufacturing 37, 101634 (2021). Rietema, M.J. Design of a prototype machine for 3D printing with continious fibre reinforcement. 2015. Zhang, H., Chen, J., Yang, D. Fibre misalignment and breakage in 3D printing of continuous carbon fibre reinforced thermoplastic composites. Additive Manufacturing 38, 101775 (2021). Becker, C., Oberlercher, H., Heim, R.B., Wuzella, G., Faller, L.-M., Riemelmoser, F.O., Nicolay, P., Druesne, F. Experimental Quantification of the Variability of Mechanical Properties in 3D Printed Continuous Fiber Composites. Applied Sciences 11(23), 11315 (2021). Liu, F., Ferraris, E., Ivens, J. Mechanical investigation and microstructure performance of a two-matrix continuous carbon fibre composite fabricated by 3D printing. Journal of Manufacturing Processes 79, 383–393 (2022). Tang, H., Sun, Q., Li, Z., Su, X., Yan, W. Longitudinal compression failure of 3D printed continuous carbon fiber reinforced composites: An experimental and computational study. Composites Part A: Applied Science and Manufacturing 146, 106416 (2021). Terekhina, S., Egorov, S., Tarasova, T., Skornyakov, I., Guillaumat, L., Hattali, M.L. In-nozzle impregnation of continuous textile flax fiber/polyamide 6 composite during FFF process. Composites Part A: Applied Science and Manufacturing 153, 106725 (2022). Wang, F., Wang, G., Ning, F., Zhang, Z. Fiber–matrix impregnation behavior during additive manufacturing of continuous carbon fiber reinforced polylactic acid composites. Additive Manufacturing 37, 101661 (2021). Kuba, D., Matsuzaki, R., Ochi, S., Ogihara, S. 3D printing of composite materials using ultralow-melt-viscosity polymer and continuous carbon fiber. Composites Part C: Open Access 8, 100250 (2022). Heathman, N., Koirala, P., Yap, T., Emami, A., Tehrani, M. In situ consolidation of carbon fiber PAEK via laser-assisted automated fiber placement. Composites Part B: Engineering 249, 110405 (2023). Schiel, I., Raps, L., Chadwick, A.R., Schmidt, I., Simone, M., Nowotny, S. An investigation of in-situ AFP process parameters using CF/LM-PAEK. Advanced Manufacturing: Polymer & Composites Science 6(4), 191–197 (2020). Yap, T., Heathman, N., Shirani Bidabadi, B., Motta de Castro, E., Tamijani, A.Y., Asadi, A., Tehrani, M. In-plane properties of an in-situ consolidated automated fiber placement thermoplastic composite. Composites Part A: Applied Science and Manufacturing 188, 108525 (2025). Toray Cetex® TC1225 LMPAEK™ Product Data Sheet, 2023. https://bit.ly/3JtGQ0m . (Accessed 12/12/2023 2023). Yap, T., Tamijani, A.Y., Tehrani, M. Aerospace Quality In-situ Consolidated Thermoplastic Composite Structures via Automated Fiber Placement: Effects of Staggering on Part Performance. AIAA SCITECH 2023 Forum. Zhang, K., Zhang, H., Wu, J., Chen, J., Yang, D. Improved fibre placement in filament-based 3D printing of continuous carbon fibre reinforced thermoplastic composites. Composites Part A: Applied Science and Manufacturing 168, 107454 (2023). Audoit, J., Rivière, L., Dandurand, J., Lonjon, A., Dantras, E., Lacabanne, C. Thermal, mechanical and dielectric behaviour of poly(aryl ether ketone) with low melting temperature. Journal of Thermal Analysis and Calorimetry 135(4), 2147–2157 (2019). Burgani, T.d.S., Alaie, S., Tehrani, M. Modeling Flexural Failure in Carbon-Fiber-Reinforced Polymer Composites. Journal of Composites Science 6(2), 33 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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-5412244","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":382478840,"identity":"1f764a0c-aa2d-47aa-a759-b4a494ec447d","order_by":0,"name":"Nathaniel Heathman","email":"","orcid":"","institution":"The University of Texas at Austin","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Nathaniel","middleName":"","lastName":"Heathman","suffix":""},{"id":382478843,"identity":"b2c654e3-db72-4264-8154-1567b7bf16f6","order_by":1,"name":"Michael DeLay","email":"","orcid":"","institution":"Mantis Composites","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Michael","middleName":"","lastName":"DeLay","suffix":""},{"id":382478845,"identity":"eee4984b-ef78-4e05-b3ba-257d6326eda3","order_by":2,"name":"Mehran Tehrani","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtklEQVRIiWNgGAWjYFACHhAhIQcmGRiYidEA0WJMshaGxAaitdiz9x778HOHRfqG48cf3mCosAbrxW8Lz7nkmb1nJHI3nMkxtmA4k06EFokcYwbeNqCWGzxsEoxth4nQIv/GmPFvm0S6wQ32ZxKM/4jRIsFjzAy0JcHgBoOZBGMDMVqAXmCWbZMwnAnyS8KxdGOCWtjbzxgzvm2rk+cDhdiHGmtZglpQQQJpykfBKBgFo2AU4AIAqfs3lY9+ogEAAAAASUVORK5CYII=","orcid":"","institution":"University of California, San Diego","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Mehran","middleName":"","lastName":"Tehrani","suffix":""}],"badges":[],"createdAt":"2024-11-07 20:38:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5412244/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5412244/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":69906517,"identity":"23de9d90-5884-45e6-861a-5d39685ee7f8","added_by":"auto","created_at":"2024-11-26 13:02:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":72260,"visible":true,"origin":"","legend":"\u003cp\u003eDSC curves for: a) the as-delivered filament, melted then fast cooled, and melted then slow cooled samples, and b) as-printed and annealed SBS samples.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/65f90aa14ab655cee6dea3c0.png"},{"id":69906520,"identity":"cf609406-46ba-4846-84ec-785f726ae7b6","added_by":"auto","created_at":"2024-11-26 13:02:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":711583,"visible":true,"origin":"","legend":"\u003cp\u003ea) µCT tomograph of an as-printed SBS coupon, with b) a 3D reconstruction of the voids in green.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/1d954f5ddf4a31f2265bc55a.png"},{"id":69905938,"identity":"086252f9-25c9-4c14-8083-db994eb478d0","added_by":"auto","created_at":"2024-11-26 12:54:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":96637,"visible":true,"origin":"","legend":"\u003cp\u003eLoad-displacement curves for a) SBS, b) flexural, and c) CBS tests.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/b0347d2ab50109efbc1b57a2.png"},{"id":69905934,"identity":"5db44e23-be11-4df6-ac68-9604ab5f6f97","added_by":"auto","created_at":"2024-11-26 12:54:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":590828,"visible":true,"origin":"","legend":"\u003cp\u003eFractographs of: a) a flexural test sample fracture surface, b) an SBS coupon after testing showing inelastic deformation and buckling, and c) a CBS coupon fracture in plane, with d) the same fracture viewed out of plane.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/7d5840e2ac86400c5f6dd78e.png"},{"id":69905943,"identity":"3187cc94-0758-4b06-a53d-31031564177f","added_by":"auto","created_at":"2024-11-26 12:54:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":366336,"visible":true,"origin":"","legend":"\u003cp\u003eFracture surface SEM images of: a) a flexural test sample fracture surface zooming in to the tensile region, and b) an SBS coupon fracture surface. Note that the SBS coupon was split apart manually for the purposes of imaging.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/d5d3d4e9994bbaac265fe2d7.png"},{"id":69906518,"identity":"e6ecf703-480f-452a-b147-2bcb23b02dce","added_by":"auto","created_at":"2024-11-26 13:02:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":301385,"visible":true,"origin":"","legend":"\u003cp\u003eµCT tomographs of steered fibers in the steering radii specimens of a radius of: a) 1.25 mm, b) 5 mm, c) 10 mm, d) 20 mm, e) 50 mm, and f) 100 mm, and g) µCT tomographs of steered fibers in the CBS sample (interior radius of 6.4 mm).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/fc5a6ebc91bd94547532ff80.png"},{"id":69905939,"identity":"e1f69d42-5aba-47b4-8b8f-99031635ef01","added_by":"auto","created_at":"2024-11-26 12:54:21","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":456007,"visible":true,"origin":"","legend":"\u003cp\u003ea) A schematic of the conformal out-of-plane ME manufacturing of the geometric bracket (in white) on a mold (in pink), with b) the top view of the asymmetrical bracket showing planned fiber paths, and c) the final printed part as removed from the mold.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/5c6bbec0d87970a18cd3c261.png"},{"id":69905942,"identity":"028fa940-4f6a-47a7-a89a-fc624fa4a8ab","added_by":"auto","created_at":"2024-11-26 12:54:21","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":444598,"visible":true,"origin":"","legend":"\u003cp\u003ea) The geometric bracket under µCT analysis, with red boxes highlight scanned sections, b) a tomograph and c) void reconstruction of the corner region, and d) a void reconstruction in the slope region, parallel to fibers, and e) perpendicular to fibers.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/e884693a2e16d1e360e83283.png"},{"id":69907365,"identity":"00913238-d9e5-41ee-bf46-c571f8eb1a66","added_by":"auto","created_at":"2024-11-26 13:10:21","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":23288,"visible":true,"origin":"","legend":"\u003cp\u003eASTM mechanical property tests: a) short beam strength, b) flexural properties, and c) curved beam strength.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/73a691c3fafde5b167f61ad2.png"},{"id":73826591,"identity":"dae3a3e4-9868-40c3-9efd-5952876313ae","added_by":"auto","created_at":"2025-01-15 05:34:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4073913,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5412244/v1/3cb0e2d7-0995-4581-a31f-9636e64571ef.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Five-axis material extrusion of high-performance structural parts with continuous carbon fiber-reinforced LM-PAEK","fulltext":[{"header":"1.\tIntroduction","content":"\u003cp\u003eMaterial extrusion (ME), also known as fused filament fabrication (FFF) or Fused Deposition Modeling\u0026trade; (FDM\u0026trade;), is an additive manufacturing (AM) technique that has been widely adopted and employed in recent years for a variety of applications, including prototyping, hobbyist parts, and, increasingly in recent years with advancements of material and process technologies, end-use components. ME brings several key advantages over conventional manufacturing techniques. First, ME allows the production of intricate geometries by optimizing designated paths (rasters or beads) and part geometry for specific loading situations, such as steering rasters around fastener holes. This can result in the production of parts with significantly higher specific performance but at a fraction of the weight and associated material costs. Second, ME can significantly reduce the amount of tooling (molds) required as compared to other conventional manufacturing techniques. If molds are still required during the ME process, they may be manufactured in-situ using relatively inexpensive materials. These molds (typically referred to as \u0026ldquo;supports\u0026rdquo; in AM) require little post finishing and can have reduced volume and complexity.\u003c/p\u003e \u003cp\u003eIn ME systems, a heated deposition nozzle (also called a hot end) attached to a positioning system is employed to melt and deposit the feedstock material, commonly a thermoplastic polymer, in rasters [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. The rasters cool and solidify quickly after deposition to form layers, and the layers are deposited one on top of another to form a complete three-dimensional shape. ME printers can utilize either gantry-based positioning systems to deposit one 2-dimensional layer at a time at a given z-axis spacing, or robotic positioning systems to take advantage of placement in all three dimensions at once, called multi-axis or out-of-plane 3D printing [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe most common ME feedstock material is a thermoplastic polymer in the form of a filament with a circular cross section of a consistent diameter; however, certain equipment can also utilize thermoplastic pellets fed via a hopper [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Traditionally, low-cost low-strength commodity thermoplastics such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and nylon have been used to manufacture parts via ME. In recent years, high-performance thermoplastics, such as polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) from the polyaryletherketone (PAEK) family, or ULTEM\u0026trade; 1010, a polyetherimide, are being increasingly used, enabling ME parts for end use in high-strength and high-temperature applications [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo push the boundaries of ME even further, fibers have been incorporated into feedstock filaments to print composite parts with superior fiber-direction mechanical properties and enhanced thermal properties as compared to their neat counterparts [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. While short discontinuous fibers have been shown to increase the strength and stiffness of ME parts, a much larger advantage comes with utilizing continuous fibers [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The ME of continuous fiber reinforced polymers takes advantage of: a) fiber lengths that are much higher than the critical fiber length of the composite system, as well as b) higher fiber volume fractions, due to the packing of aligned fibers, to achieve specific mechanical properties that are approximately one to two orders of magnitude higher than those of their short fiber counterparts [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. It must be noted that these mechanical properties are measured in the longitudinal fiber direction (i.e., fiber-dominated properties). A variety of polymer matrices and fibers can be used in the process; the former includes ABS, PLA, nylon, and the PAEK family of polymers, while the latter includes glass, Kevlar, and carbon fibers [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The emergence and widespread adoption of carbon fiber reinforced polymers (CFRPs) is one of the main developments in enabling ME technology for end-use components. With high strength and stiffness to weight ratios, these materials are directly applicable for use in high performance applications in the automotive, energy, and aerospace industries where high strength, low weight, and high temperature performance are required [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. By combining CFRPs with AM technology, it becomes possible to leverage the benefits of AM processes to exploit the material advantages of CFRPs.\u003c/p\u003e \u003cp\u003eHowever, when choosing to use continuous fibers rather than using short discontinuous fibers or neat feedstocks, a key change has to be made to the ME process involving the path planning for how the filaments are laid down during each layer. As opposed to short fiber or neat ME, the continuous fiber process must utilize a continuous path for each raster with a prescribed start and stop, due to the necessity to cut the filament at the end of each raster [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Typically, a minimum distance between start and stop is required due to machine limitations; each layer can have multiple rasters as long as this requirement is met. While this complication may seem detrimental, it in fact opens an opportunity to optimize the design of continuous fiber ME parts for particular loading situations in a way which increases specific strength and stiffness [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAdditionally, the user must consider the manner in which continuous fibers are incorporated into the filament. There are two main methods: either using filaments that have been pre-impregnated with fibers via a melt impregnation process, or combining fibers and polymer together within the hot end immediately before printing [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]; care must be taken to ensure the proper wetting of fibers within the polymer [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The former method is used in this study.\u003c/p\u003e \u003cp\u003eAs with neat ME, the success of continuous fiber ME is highly dependent on processing parameters to develop ideal properties in the final part. Process speed, layer height and width, as well as nozzle, bed, and chamber temperatures are all critical parameters to the ME process, where each parameter has to be finely tuned for specific materials and printer types [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In the case of the manufacturing of high-performance amorphous and semi-crystalline polymers such as polyetherimide (PEI), polybenzimidazole (PBI), polyphenylene (PPS), and PAEKs, high nozzle, bed, and chamber temperatures along with slow speeds are typically required to consolidate the layers, and to achieve maximum crystallization if a semi-crystalline polymer is used [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Interlaminar bonding, degree of crystallinity, void development, and fiber misalignment and breakage are all significant mechanisms that contribute to the overall strength of parts manufactured via continuous fiber ME [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. These mechanisms will now be discussed.\u003c/p\u003e \u003cp\u003eInterlaminar bonding is the main factor governing the overall performance of continuous fiber ME parts, especially when subjected to loads that are not in the fiber direction [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. This is a matrix-dominant property; in contrast, the performance of a printed part in the fiber direction is a fiber-dominant property that is unlikely to vary with different processing conditions [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Compared to thermoforming, where the polymer/fibers are heated uniformly to melting temperature under compressive forces and are then allowed to cool at a controlled rate, the ME process deposits molten material on top of an already cooled layer, relying largely on the heat in the extrudate to transfer to the previous layer [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The temperature in the previous layer thus heats up above glass transition temperature (T\u003csub\u003eg\u003c/sub\u003e) and into the melt window where polymer can flow and its chains inter-diffuse across the interface to achieve bonding between the layers [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. As such, the level of interlaminar bonding is highly dependent on the viscosity of the polymer and the time at which the two layers are in contact above T\u003csub\u003eg\u003c/sub\u003e. Generally, in ME processes, the cooling rates are very high (in the order of hundreds of K/s), which result in poor inter-diffusion and consequently poor interlaminar bonding. Bonding can, therefore, be significantly improved by the use of heated chambers and print beds, or, in certain cases, preheating the previous layer [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe degree of crystallinity must be considered when utilizing high-performance semi-crystalline polymers, such as those belonging to the PAEK family, as the crystallization process is significant to the overall part strength. Crystallinity in polymers refers to the self-organization of polymer chains into ordered groupings within the amorphous regions where polymer chains are disorganized. Crystalline regions provide significant improvements to overall strength, stiffness, increased toughness, and wear resistance when compared to their amorphous counterparts [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Primarily, crystallization occurs above T\u003csub\u003eg\u003c/sub\u003e as the part is cooled from melt when polymer chains organize into repeating units called lamella; these lamellae grow and align, forming spherulites or spherical groupings of crystalline polymer chains [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Crystallinity is highly dependent on cooling rate, as the ability of polymer chains to nucleate and grow spherulites is directly related to the time spent in the crystallization window [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. This is of specific importance to the ME process due to the inherently high cooling rates observed during ME [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]; evidence shows high crystallinity is very difficult to achieve during the ME process. It should be noted that generally crystallinity is assumed to directly impede the inter-diffusion of polymer chains as previously described [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAnother type of crystallization that can occur during the ME process is cold crystallization, where a material has its polymer chains regain mobility and begin to organize when temperature is held above the cold crystallization temperature (T\u003csub\u003ecc\u003c/sub\u003e) [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. To this end, manufacturers may recommend annealing of ME-printed parts, where the printed material is at first held at T\u003csub\u003eg\u003c/sub\u003e in the chamber to promote polymer inter-diffusion across layers, while at the same time having minimal crystallinity due to the high cooling rates from melt. Annealing is performed afterwards where the chamber temperature is further raised to T\u003csub\u003ecc\u003c/sub\u003e to promote crystal growth across layers. This high level of crystallinity therefore contributes to greater overall strength. A previous study by the authors on short carbon fiber-reinforced PEEK and PEKK found that the high level of degree of crystallinity of the former impeded the inter-diffusion of polymer chains across layer boundaries, resulting in a low interlaminar tensile strength of \u0026lt;\u0026thinsp;20 MPa. The latter\u0026rsquo;s lower degree of crystallinity immediately after printing allowed for greater polymer chain inter-diffusion; the crystallinity increased only upon post-annealing, resulting in an improved interlaminar tensile strength of ~\u0026thinsp;50 MPa. For comparison, the longitudinal tensile strength of either composite material is ~\u0026thinsp;100 MPa.\u003c/p\u003e \u003cp\u003eVoid development in CRFPs manufactured via ME can significantly impact mechanical properties [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The appearance of voids is inherent to the ME process due to the stacking of the extruded beads of an elliptical shape that creates diamond-shaped or triangular voids at each raster boundary [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Furthermore, in the ME of fiber reinforced polymers, voids may already be present within the feedstock filament itself and can be passed onto the part [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]; these voids appear in the filament due to a low polymer matrix-fiber adhesion, or inability to fully impregnate the fibers with polymer [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Voids will therefore lower interlaminar properties due to stress concentrations and the reduction of effective cross-sectional area [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Successful attempts to eliminate voids in ME parts have been made using several different methods. In one study, a significant reduction of inter-raster voids in a neat polymer was made by increasing the extrusion rate (amount of material deposited) to increase the inter-raster pressures allowing the molten material to flow and fill these areas [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Another method proposed for void reduction is utilizing a heated compaction roller that follows the hot end to compress the rasters, thereby decreasing the void content [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Hot isostatic pressing (HIP) has also been utilized, where an ME-manufactured part is subjected to elevated temperatures and isostatic pressures in a post processing step to remove voids and increase interlayer bonding [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. The latter methods may also give the side benefit of increasing interlaminar intimate contact.\u003c/p\u003e \u003cp\u003eMinimizing fiber misalignment and breakage during the ME of continuous fiber filaments presents a particular challenge [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. During printing, fibers are aligned in the direction of travel of the print head. Due to the fixed orientation of the deposition nozzle, fibers resist a change in direction during the print, which can lead to twists, overlaps, and void formation between fibers any time the print direction is altered. In a study using polyamide 6\u0026thinsp;\u0026minus;\u0026thinsp;1 continuous carbon fiber filaments, samples were prepared at various radii and angles to inspect the behavior of the fibers under different curvatures [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. While fibers are well aligned with minimal voids at high radii, print defects occurred at smaller radii, including path errors, fiber twisting, folding, and misalignment, along with the formation of voids. Considering these defects are inherent with the process, it is important to note their occurrence and be able to adjust raster paths to mitigate their occurrence, ensuring the highest strength possible in the manufactured parts.\u003c/p\u003e \u003cp\u003eThe mechanisms of interlaminar bonding, degree of crystallinity, void development, and fiber misalignment and breakage have now been discussed for their overall contribution to mechanical properties in parts manufactured via continuous fiber ME. With the development of off-the-shelf printers using continuous fiber filaments by a variety of manufacturers such as Markforged, 9T Labs, Desktop Metal, Anisoprint, Arevo, and others, mechanical properties are beginning to be well documented specifically for lower grade materials [\u003cspan additionalcitationids=\"CR43 CR44 CR45\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. However, much less research has been conducted on semicrystalline high-performance thermoplastics. In one study, van de Werken et al. sought to investigate the mechanical and thermal properties and microstructure of ME parts using AS4C continuous carbon fiber PEEK filaments with a 42% fiber volume fraction (v\u003csub\u003ef\u003c/sub\u003e), both in as-printed form as well as after a HIP post processing procedure [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Results show as-printed samples achieved a short beam strength (SBS) of 27 MPa, flexural strength of 834 MPa, a void content of 10%, and a degree of crystallinity of 22%. When subjected to HIP at 200 psi and 250 ˚C, SBS was increased to 35 MPa and flexural strength to 1221 MPa, with the void content decreased to 5% and the degree of crystallinity increasing slightly to 23%. Kuba et al. studied the effect of melt viscosity on void content and interlaminar tensile strength of specimens manufactured from three different grades of PEEK using continuous fiber ME [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. Tests revealed that the lower melt viscosity filament halved the void content and more than doubled the interlaminar tensile strength when compared to the standard viscosity material, providing significant evidence that reducing melt viscosity in semi-crystalline materials helps improve bonding strength and reducing void content. Meng et al. employed a laser preheating technique in the continuous fiber ME process to enhance interlaminar bonding and tested its effectiveness by manufacturing and testing two viscosity grades of PEEK in a 38 wt.% carbon fiber filament [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. With laser preheating enabled, a maximum short beam strength, flexural strength, and flexural modulus of 36 MPa, 480 MPa, and 37 GPa, respectively, were achieved. While these studies show a variation in flexural strength and void content, the low short beam strength values remain consistent, with the conclusion that PEEK suffered from too high of a melt viscosity to enable sufficient polymer flow, polymer chain mobility and interfacial diffusion for maximizing interlaminar bonding in the continuous fiber ME process. An alternate suggestion was made that premature crystallization occurred prior to polymer interdiffusion across interfaces, which minimized intimate contact and consequently lowered short beam strength.\u003c/p\u003e \u003cp\u003eIt should be noted that the aforementioned examples used modified gantry-based 3D printers; the authors were unable to find studies on the ME of continuous fiber-reinforced semicrystalline high-performance thermoplastic composite materials using a multi-axis 3D printer.\u003c/p\u003e \u003cp\u003eThis paper aims to utilize a new high-performance semi-crystalline material from the PAEK family, denoted as low-melt PAEK (LM-PAEK\u0026trade;), to manufacture specimens using a commercially available multi-axis 3D printer and analyze their thermal, microstructural, and mechanical properties. LM-PAEK, while providing similar strength, high temperature performance, chemical and wear resistance to PEEK, offers a lower melting temperature and viscosity, which in turn should help to alleviate the interlaminar bonding challenges as seen in previous research of continuous fiber ME of PEEK. Samples were manufactured with and without an annealing post process step, and the resultant ASTM standardized properties of both sets of samples were compared. Further custom specimens were manufactured to understand the effects of steering radii and the utilization of the out-of-plane axis on void content. The results provide an understanding into the properties achieved with this new material in the continuous fiber ME process and can drive advancement of continuous fiber-reinforced ME beyond previous insights developed with lower grade materials or with gantry-based systems.\u003c/p\u003e"},{"header":"2.\tResults ","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e\u003cspan class=\"SmallCaps\"\u003e2.1 Thermal and microstructural characterization\u003c/span\u003e\u003c/h2\u003e\n \u003cp\u003eDSC was first performed on the feedstock filament. Figure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea shows DSC curves for the filament in three forms: as delivered, heated to melt and cooled at 500 K/min (denoted as fast cooled), and heated to melt and cooled at 1 K/min (denoted as slow cooled). The as-delivered filament showed a 7% crystallinity, a 5% minimum with fast cooling, and a 25% maximum with slow cooling. These values are typical of carbon fiber LM-PAEK [\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e]. All samples exhibited a T\u003csub\u003eg\u003c/sub\u003e of ~\u0026thinsp;150\u0026deg;C. Slow-cooled samples demonstrated a slightly higher melting peak compared to the other two samples. All samples melted below the processing nozzle temperature of 340\u0026deg;C used here.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eDSC was then performed on selected portions of the SBS and CBS samples to inspect the development of crystallinity during the manufacturing process. In ME, the cooling rate from the melt is expected to be rapid (in the order of hundreds of Kelvins per second) [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e50\u003c/span\u003e]. The use of a heated bed at 200\u0026deg;C, as employed in this study, may enable cold crystallization to occur within relatively short samples. However, taller samples are expected to cool at similar rates but may not remain near 200\u0026deg;C, and hence may not achieve a large degree of cold crystallization.\u003c/p\u003e\n \u003cp\u003eDegree of crystallization values as measured from several locations in different specimens are summarized in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. SBS samples, with DSC curves provided in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb, showed a near maximum crystallinity of ~\u0026thinsp;24% developed at the bottom and middle of the sample, but crystallinity was only 7% at the top surface of the sample. The annealed samples on the other hand had a consistent crystallinity of ~\u0026thinsp;24% through the entire height of the sample. Given that the SBS samples were 6 mm tall, the effects of the heated print bed were only noticeable within a few millimeters, which helped the deposited rasters to crystallize by sustaining their temperatures for sufficient durations within the cold-crystallization window. Regardless, the annealing procedure resulted in near maximum crystallinity values throughout the z-height of all samples, and should therefore be recommended for samples taller than 3 mm. The procedure may eliminate residual stresses and is not expected to result in sample deformations.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eCrystallinity values for different samples at multiple locations.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSample and location\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCrystallinity (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSBS sample, as-printed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6 mm from print bed (top)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 mm (middle)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 mm (bottom)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSBS sample, annealed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6 mm (top)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 mm (bottom)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS sample\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e25 mm (top)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.5 mm (middle)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 mm (bottom)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe height-dependent difference in crystallinity was also shown in the CBS samples (printed on their side), which had a relatively high crystallinity at the bottom but had a lower crystallinity of ~\u0026thinsp;11% at the middle and top of the sample, 12.5 mm and 25 mm from the print bed, respectively. Results are given in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eAn interesting phenomenon in the SBS sample DSC curves, as in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb, is the double melting curve. Previous research has shown that this is a result of isothermal holds above glass transition temperature where there is a primary crystallization process where spherulitic entities are formed, and a secondary process, where interlamellar crystalline structures grow [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e]. The double melting curves appeared in the DSC curves at approximately 10 to 30 ˚C above the isothermal hold temperatures (200 ˚C for the as-printed parts and 210 ˚C for the annealed parts) [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003e\u0026micro;CT was conducted on an as-printed SBS coupon. A tomograph of an as-printed SBS coupon is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea. A 1.63% void volume content was measured by analyzing the \u0026micro;CT slices; voids were predominantly located at filament interfaces and travel longitudinally along the interfaces for long distances within the sample. These voids were segmented during \u0026micro;CT analysis from the sample and reconstructed in three dimensions to demonstrate how they are located within the sample, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb. As previously found for neat thermoplastic ME parts [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e], diamond shaped voids are expected to form between individual rasters due to the oval shape of the deposited filaments. However, in the continuous fiber ME process studied here, voids appeared at random predominantly on the raster boundaries, with a small portion of voids appearing within the rasters themselves. This suggests that voids appeared at interfaces due to incomplete intimate contact (lack of flow and interdiffusion), which was in turn caused by a lack of pressure to facilitate polymer flow, whereas the voids within the rasters could be from the feedstock filament. The measured void content in this study is significantly lower compared to previous literature on continuous fiber-PEEK ME parts, 10% in one study and 8% in another [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e]. Considering the similar manner of fabrication for the aforementioned PEEK specimens, the lower void content presented here suggests that the lower viscosity at melt for LM-PAEK was the driving factor for the low void content. It should be noted that while the void content is low, the voids are elongated and present at most raster-raster and layer-layer interfaces, which may reduce the interlaminar shear strength.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eUp to this point, full thermal and microstructural analyses for the samples with and without post processing have been presented. These will in turn affect and explain the mechanical properties as described in the next section.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e\u003cspan class=\"SmallCaps\"\u003e2.2 ASTM standardized mechanical property characterization and fractography\u003c/span\u003e\u003c/h2\u003e\n \u003cp\u003eResults for all mechanical tests are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and representative loading curves are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Analyses of the mechanical testing results show multiple interesting phenomena and are presented alongside fractography in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e and SEM imaging in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMechanical property results.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eProperty\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eValue\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFlexural test, as-printed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStrength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e943\u0026thinsp;\u0026plusmn;\u0026thinsp;24\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMaximum strain (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eChord modulus (GPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e84\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFlexural test, annealed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStrength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e930\u0026thinsp;\u0026plusmn;\u0026thinsp;44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMaximum strain (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eChord modulus (GPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e86\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eShort beam strength, as-printed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSBS (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eShort beam strength, annealed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSBS (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60\u0026thinsp;\u0026plusmn;\u0026thinsp;3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCurved beam strength\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCBS (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e62\u0026thinsp;\u0026plusmn;\u0026thinsp;7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eFlexural testing is a common test to assess intra-laminar properties of composites, and flexural failure is typically fiber compression under a mixed stress mode. A mean flexural strength of 943 MPa was achieved for the as-printed coupons, which is higher than any as-printed result found in previous studies [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. Flexural modulus was 84 GPa, which is expected following the rule of mixtures: 37% fiber volume fraction and standard modulus carbon fibers (modulus of 230 GPa).\u003c/p\u003e\n \u003cp\u003eAnnealing flexural coupons did not change the mechanical properties outside the error bounds. Given the small height of the coupons (4 mm), all parts of the printed coupons are expected to benefit from the proximity to the heated print bed and achieve a near maximum crystallinity of ~\u0026thinsp;24% measured for the bottom half of the SBS coupon (see Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). Interlaminar properties are therefore expected to remain the same during annealing.\u003c/p\u003e\n \u003cp\u003eFractography was performed to investigate failure modes as in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. The flexural samples showed a typical fracture surface with clearly defined tensile and compression stress states as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea where a sharp jagged fracture surface is indicative of tensile failure and a smooth flat fracture surface is indicative of compression loading. No delamination was observed in flexural samples as is expected for the span-to-thickness ratio. SEM imaging of the flexural samples was conducted as per Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e to inspect the fiber-matrix interfaces on fracture surfaces. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea shows a magnified area of the flexural sample under tensile stress. Analysis of this region shows multiple fibers bundled together with polymer matrix, a small number of individual fibers pulled out of the bundles, and overall, very few clean fibers. Overall, inspection of the fracture surface via SEM imaging shows significant evidence of a strong fiber-matrix interphase region, which can also be expected to contribute to various other mechanical properties not tested in the flexural tests such as interlaminar shear strength or transverse tensile strength.\u003c/p\u003e\n \u003cp\u003eThe SBS test is similar to the flexural test, except that given the change to the span-to-thickness ratio, failure is expected to occur via interlaminar shear rather than intra-laminar tensile and/or compressive failure. The 60 MPa as-printed SBS strengths achieved here is significantly higher than the maximum SBS values of ~\u0026thinsp;35 MPa found in other studies of continuous fiber PEEK ME parts [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e]. However, these as-printed strength values are only\u0026thinsp;~\u0026thinsp;60% of compression molded LM-PAEK parts, with a manufacturer-reported SBS strength\u0026thinsp;~\u0026thinsp;95 MPa [\u003cspan class=\"CitationRef\"\u003e51\u003c/span\u003e]. While these SBS values still fall short of those for compression molded samples, 60 MPa is considered relatively high for a part manufactured via ME where intimate contact and interdiffusion between layers suffer due to high cooling rates and dissimilar layer temperatures during deposition, although intimate contact and interdiffusion is expected to improve due to the proximity to the heated print bed. Annealing did not affect the SBS results, as shear failure occurred predominantly in the middle region of the coupon, which had the same degree of crystallinity with or without annealing as reported in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb shows a side profile an as-printed SBS sample after testing. The observed failure mode for all as-printed and annealed SBS samples is inelastic deformation with a small amount of crushing under the loading roller. This failure mode is representative of a large amount of plastic deformation without apparent delamination on the coupon edges. Inspection of the loading curves in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea shows clear plastic deformation and no sharp drop-offs in loading indicative of delamination. SBS failure behavior presented here is different than traditional samples manufactured by hand lay-ups or automated fiber placement where significant shear failure and delamination occurs, evident by the appearance of a few cracks near the middle of the sample [\u003cspan class=\"CitationRef\"\u003e52\u003c/span\u003e]. The presence of several smaller cracks at interlaminar regions, Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea-b, could be the reason for the gradual (several smaller and internal shear delaminations) failure behavior in ME samples as compared to sudden failure in samples manufactured by other methods.\u003c/p\u003e\n \u003cp\u003eGiven the inelastic deformation failure of the SBS samples, a crack was initiated at the end of the sample with a razor blade and split manually in order to image the interfaces under SEM to inspect the fiber-matrix interfaces. This fracture surface is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb, where the most notable feature is the remnant of the polymer matrix on the fibers. Combined with the insights from the flexural coupon in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea, overall SEM fractography shows significant evidence of a strong fiber-matrix interphase region which is expected to improve matrix-dominated transverse and through-thickness (interlaminar) direction properties.\u003c/p\u003e\n \u003cp\u003eThe CBS testing method typically induces an out-of-plane tensile stress within the curved region of the specimen, specifically through its thickness if manufactured on a curved mold. However, in order to investigate the transverse-direction properties, the sample was printed on its side; in this case, the measured tensile strength would be in the inter-raster transverse direction. CBS testing results show the resultant maximum inter-raster tensile strength of 62 MPa. However, upon inspection of the fractured coupon, not only does the in-plane fracture surface in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec show clear tensile stress induced fractures in between rasters as expected, but the out of plane surface shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed also shows delamination and buckling between layers. While the latter phenomenon is unexplained in the context of the ASTM standard, it can be theorized that the delamination is: a) a result of complex 3D stresses arising from fiber misalignments in the 6.4 mm radius bend during manufacturing (note that all previous coupons did not have curved rasters), and/or b) variations in local matrix properties caused by crystallinity changes throughout the 25 mm tall sample contributed to the delamination; the CBS sample was not post-annealed, and therefore achieved a low crystallinity in the regions far away from the bed that are shown as failed in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed. Further \u0026micro;CT characterization is discussed in the next section to explain these anomalous fracture patterns.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e\u003cspan class=\"SmallCaps\"\u003e2.3 \u0026micro;CT characterization of steering radii specimens and CBS sample\u003c/span\u003e\u003c/h2\u003e\n \u003cp\u003eSteering is recognized for its tendency to cause fiber misalignments, although current understanding of this process remains limited even as steering is commonly employed in ME. The observed failure behavior in the CBS test underscores the importance of gaining further insight into the steering process. To this end, the CBS sample was scanned, and a tomograph is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. Furthermore, steering radii specimens were manufactured and then scanned with \u0026micro;CT, and their reconstructions are also shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea shows the tomographic image of a printed filament (one single raster) at a radius of 1.25 mm, the minimum printable with the Mantis Composites machine, where the fiber path was steered to align directly next to the previous path. It is clear that the fibers folded over one another to round the corner as opposed to being steered. As the radius decreased from 1000 mm to 1.25 mm, as in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ef through Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea, fibers tended to be unable to conform to the steering angle and tended to fold over, wrinkle, and twist as opposed to following the programmed path. This trend was even more evident in the interior of the curved regions, where the radius is smaller than the exterior. This phenomenon can be explained by the different forces experienced in the individual filaments during deposition: the interior of the curve would be under compression, where the exterior portion would be under tension [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]. The compressive forces caused fibers to buckle whereas the tensile forces caused the fibers to fold over one another. Additionally, voids may be introduced in the twisted regions, as evidenced in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ee and in the CBS sample as in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eg, and might have acted as stress concentrations. As such, the combination of fiber wrinkling and folding, interlaminar and intra-laminar voids, and stress concentrations might have resulted in the failure modes and cracks as previously detailed in CBS fractography.\u003c/p\u003e\n \u003cp\u003eOne possible solution to this issue is the development of a rotating deposition nozzle that manually twists the filament during deposition in corners to relieve these stresses [\u003cspan class=\"CitationRef\"\u003e53\u003c/span\u003e]. Alternatively, compression molding may succeed in closing up these intralaminar voids.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e\u003cspan class=\"SmallCaps\"\u003e2.4 Manufacturing and \u0026micro;CT characterization of geometric bracket\u003c/span\u003e\u003c/h2\u003e\n \u003cp\u003eTo highlight the out-of-plane printing capability of the continuous fiber ME process in the machine developed by Mantis Composites, a complex 3-dimensional geometric bracket was manufactured and analyzed for overall quality. Figure\u0026nbsp;7a-b show the nozzle path and orientation for the bracket shown in Fig.\u0026nbsp;7c. The geometric bracket was printed on a heated metal mold, following a path that formed a single continuous loop. The orientation of the nozzle was maintained perpendicular to the mold\u0026rsquo;s surface. Processing parameters such as speed and temperature were varied depending on the location in the path to optimize the part quality. Given the varying process parameters and nozzle travel orientation during the print, part properties may vary from one location to the next. It is critical to analyze and note any variations in quality.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003eThe geometric bracket was imaged with \u0026micro;CT in two regions of importance to view void development and defects. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea provides an image of the bracket, with boxes highlighting the two areas (named \u0026ldquo;corner\u0026rdquo; and \u0026ldquo;slope\u0026rdquo;) that were scanned. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eb shows a cross-sectional tomograph of the former corner region. In this region, the amount of voids was increased where the fibers were steered around the corner when compared to the straighter regions. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ec provides an image of the corner area with the voids reconstructed and represented in green. A void analysis of the steered section yields an 8.8% void content in the steered area, compared to 5.2% when the fibers were oriented in a straight line; for comparison, note that the SBS coupons contained\u0026thinsp;\u0026lt;\u0026thinsp;2% voids. These results validate the previous evidence of an increased void content in regions of higher curvature. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ed-e provide cross sectional tomographs of the slope region. Notable findings include the large presence of voids in this region, concentrated at the bottom of the sample where fibers were placed on the mold. Void analysis of the entire slope section yielded a 5% void content. However, when looking at Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ee, the difference in void content between the left and the right of the slope region can be seen. Note that in the left region the filament was deposited in travelling down the slope, compared to the right region where the filament was deposited traveling up the slope. The red box located in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ee highlights an area with a significantly large void volume content; this defect occurred in the area where filament was travelling down the slope. It can be theorized that while the nozzle travels down an incline, as in the left side, the direction of travel corresponding to mold angle causes a natural lifting effect on the deposited filament, producing an increased void content or large defects. Results from \u0026micro;CT analysis of this geometric bracket offer valuable insights into the quality of complex parts produced via continuous fiber ME. Designers therefore need to consider all aspects of the filament path and travel orientation to minimize the occurrence of defects in a part.\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3.\tDiscussion","content":"\u003cp\u003eIn this study, various ASTM standardized and custom complex-shaped specimens were fabricated using continuous fiber material extrusion (ME), also known as fused filament fabrication (FFF), and a newly developed semi-crystalline high-performance thermoplastic called LM-PAEK\u0026trade;. Analysis of the samples' mechanical properties, thermal properties, and microstructure revealed that LM-PAEK is well-suited for ME and outperforms other high-performance polymers in terms of part quality and performance.\u003c/p\u003e \u003cp\u003eMechanical testing demonstrated exceptional interlaminar shear strength (via short beam strength) and flexural strength of 60 MPa and 943 MPa, respectively, for the as-printed coupons. These samples also exhibited an inter-raster tensile strength (via a modified version of the curved beam strength test) of 62 MPa. As an indirect comparison, short carbon fiber-reinforced polyetheretherketone (PEEK) parts had a recorded\u0026thinsp;\u0026lt;\u0026thinsp;20 MPa interlaminar tensile strength in a previous study by the authors [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Void analysis of a printed flat coupon revealed a void volume content of 1.6%, primarily concentrated along raster interfaces. Crystallinity assessment via differential scanning calorimetry (DSC) indicated that the filament was delivered with 7% crystallinity, as compared to a maximum crystallinity of 25% achieved through slow cooling from melt. DSC testing of the samples themselves demonstrated near-maximum crystallinity at the bottom of the sample, close to the heated bed; crystallinity decreased with increasing height off the print bed. It was demonstrated that near-full crystallization of a part could be achieved through a relatively low-temperature (210 ˚C) and quick post-annealing step, with no change in the tested mechanical properties; the increased crystallization is expected to improve creep and chemical resistance properties.\u003c/p\u003e \u003cp\u003eAnalysis of micro-computed tomography (\u0026micro;CT) data obtained from single deposited filaments (\u0026ldquo;steering radii specimens\u0026rdquo;) showed significant buckling, twisting, and folding of fibers when steered around sharp corners. These defects resulted in the formation of large voids in parts with curved shapes where the filaments had to conform. Additionally, a complex geometric bracket was successfully manufactured, thereby demonstrating the viability of out-of-plane continuous fiber ME; voids similarly appeared in regions of high curvature, but also tended to appear when the nozzle travels downwards an inclined mold according to the lifting effect.\u003c/p\u003e \u003cp\u003eThe presented results highlight the ability to manufacture intricate parts with continuous fiber LM-PAEK via five-axis ME with enhanced interlaminar bonding and reduced void content compared to their PEEK counterparts. It can be theorized that the lower processing temperature and viscosity provided by LM-PAEK significantly aid in the interlaminar bonding process. Based on the findings of this study, LM-PAEK should be considered the new standard for use in continuous fiber ME of high-performance semi-crystalline polymers, and further study should be directed to the elucidation of void growth at different mold angles whenever a five-axis 3D printer is used.\u003c/p\u003e"},{"header":"4. Methods","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e4.1 Materials\u003c/span\u003e\u003c/h2\u003e \u003cp\u003eThe material used for sample fabrication is carbon fiber LM-PAEK\u0026trade; continuous fiber filament. The filament comprises AS4C carbon fiber and Victrex AE250 LM-PAEK\u0026trade; polymer. with a resulting 37% carbon fiber volume fraction (as measured via micro computed tomography of the filament) and a 0.8 mm filament diameter. LM-PAEK is a high performance semi-crystalline polymer that belongs to the PAEK group of thermoplastics and is thus similar to PEEK and PEKK. LM-PAEK has comparable mechanical properties and high chemical resistance, but provides a lower processing temperature due to a reorganization of the polymer chains into co-polymer groupings; given a melting temperature measured at 307 ˚C, its processing temperature is brought down ~\u0026thinsp;60 ˚C as compared to PEEK and PEKK [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e4.2 Fabrication of ASTM standard samples\u003c/span\u003e\u003c/h2\u003e \u003cp\u003eAll samples were fabricated with a 5-axis continuous fiber material extrusion (ME) printer developed by Mantis Composites. A nozzle speed of 10 mm/s, extruder temperature of 340 ˚C, and bed temperature of 200 ˚C were utilized; the nozzle speed was half the speed of gantry-based PEEK or PEKK nozzle speeds as found in literature [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThree types of samples were fabricated per ASTM standards for analysis: ASTM D2344 for short beam strength (SBS), ASTM D6415 for curved beam strength (CBS), and ASTM D7264 for flexural properties. SBS and flexural samples were fabricated oversize and machined to the correct sizes afterwards; owing to the bend in the shape and the difficulty in machining, CBS samples were manufactured to size on their side. After fabrication, half the SBS and flexural samples were subjected to annealing for comparison to non-annealed (as-printed) coupons; annealing consisted of heating samples from room temperature to 160 ˚C at a 3 ˚C/min rate, holding for 30 minutes, then heating from 160 ˚C to 210 ˚C at a 3 ˚C/min rate, followed again by holding for 1 hour, after which they were allowed to cool to room temperature in the oven at an uncontrolled rate. Samples were then characterized as described in a later section.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e4.3 Fabrication of custom specimens\u003c/span\u003e\u003c/h2\u003e \u003cp\u003eFollowing the ASTM standardized mechanical testing, the phenomena of fiber misalignment and fiber breakage in high-curvature turns were assessed via printing specimens of varying steering radii at a single layer height (\u0026ldquo;steering radii specimens\u0026rdquo;), with radii varying between 1.25 mm and 100 mm. Specimens were then characterized as described in a later section.\u003c/p\u003e \u003cp\u003eAdditionally, a complex 3-dimensional geometric bracket was manufactured fully utilizing the 5-axis capability of the printer, and then analyzed for defects and voids as described in a later section. Path planning was optimized to ensure that a constant fiber direction was maintained along the path of the geometric bracket.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e4.4 Characterization techniques\u003c/span\u003e\u003c/h2\u003e \u003cp\u003eThermal properties were evaluated via differential scanning calorimetry (DSC) to determine the crystallinity of the samples. DSC tests were carried out in multiple regions within each sample to form an understanding of how crystallinity developed during the printing process. A heating rate of 10 K/min was used for all DSC tests.\u003c/p\u003e \u003cp\u003eCross-sectional microscopy and micro computed tomography (\u0026micro;CT) were performed with a MicroXCT 400 Zeiss machine to analyze the microstructure of the filament and printed samples for fiber distribution, defects, and void content. Additionally, the steering radii specimens and geometric bracket were scanned with \u0026micro;CT to analyze fiber breakage and twisting as well as void development. The ImageJ and Dragonfly software were used for image analysis.\u003c/p\u003e \u003cp\u003eASTM standardized mechanical property characterization was carried out for short beam strength (SBS), curved beam strength (CBS), and flexural strength and modulus. SBS is a qualitative measure of interlaminar shear strength (ILSS) and is commonly used to assess bonding (consolidation) degree in additively manufactured composites. The CBS testing procedure utilizes a curved beam specimen comprised of two straight legs joined by a 90\u0026deg; bend with an inner radius of 6.4 mm; when a force is applied through a 4-point loading fixture, it induces an out-of-plane tensile stress within the curved region of the specimen through its thickness, and so the test is considered to be an assessment of interlaminar tensile strength (ILTS) through the thickness. Flexural testing is another common test to assess intra-laminar properties of composites [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], and the failure of flexural coupons is typically fiber compression under a mixed stress mode. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003e provides illustrations of all ASTM tests carried out.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabd\" border=\"1\"\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 \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabe\" border=\"1\"\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 \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\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/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFurther fractography of the tested coupons was conducted using optical microscopy using a Nikon D7000 camera with a 105 Sigma EX macro lens and scanning electron microscopy (SEM) using a FEI Quanta 650 ESEM machine. Samples were sputtered with a few nanometers layer of gold prior to SEM.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eCompeting interests\u003c/span\u003e \u003c/h2\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eNH: writing, validation, methodology, investigation, formal analysis, data curation. MD: methodology, manufacturing, funding acquisition, conceptualization. MT: methodology, draft review and editing, formal analysis, data curation, advising, funding acquisition, conceptualization.\u003c/p\u003e\u003ch2\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eAcknowledgements\u003c/span\u003e \u003c/h2\u003e \u003cp\u003eThe authors are grateful for the research support provided by the Air Force Research Laboratory (AFRL) award no. FA8649-21-P-0122 and the Air Force Office of Scientific Research (AFOSR) award no. FA9550-21-1-0066.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eThe corresponding author will make the data supporting this paper available upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTran, T.Q., Ng, F.L., Kai, J.T.Y., Feih, S., Nai, M.L.S. Tensile Strength Enhancement of Fused Filament Fabrication Printed Parts: A Review of Process Improvement Approaches and Respective Impact. Additive Manufacturing 54, 102724 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBadarinath, R., Prabhu, V. Integration and evaluation of robotic fused filament fabrication system. Additive Manufacturing 41, 101951 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFerreira, I., Machado, M., Alves, F., Torres Marques, A. A review on fibre reinforced composite printing via FFF. Rapid Prototyping Journal 25(6), 972\u0026ndash;988 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao, X., Qi, S., Kuang, X., Su, Y., Li, J., Wang, D. Fused filament fabrication of polymer materials: A review of interlayer bond. Additive Manufacturing 37, 101658 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrenken, B., Barocio, E., Favaloro, A., Kunc, V., Pipes, R.B. Fused filament fabrication of fiber-reinforced polymers: A review. Additive Manufacturing 21, 1\u0026ndash;16 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePandelidi, C., Bateman, S., Piegert, S., Hoehner, R., Kelbassa, I., Brandt, M. The technology of continuous fibre-reinforced polymers: a review on extrusion additive manufacturing methods. The International Journal of Advanced Manufacturing Technology 113(11), 3057\u0026ndash;3077 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evan de Werken, N., Tekinalp, H., Khanbolouki, P., Ozcan, S., Williams, A., Tehrani, M., Additively manufactured carbon fiber-reinforced composites: State of the art and perspective. Additive Manufacturing 31, 100962 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhuo, P., Li, S., Ashcroft, I.A., Jones, A.I. Material extrusion additive manufacturing of continuous fibre reinforced polymer matrix composites: A review and outlook. Composites Part B: Engineering 224, 109143 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFernandes, R.R., van de Werken, N., Koirala, P., Yap, T., Tamijani, A.Y., Tehrani, M. Experimental investigation of additively manufactured continuous fiber reinforced composite parts with optimized topology and fiber paths, Additive Manufacturing 44, 102056 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSuzuki, T., Fukushige, S., Tsunori, M. Load path visualization and fiber trajectory optimization for additive manufacturing of composites. Additive Manufacturing 31, 100942 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYamamoto, K., Luces, J.V.S., Shirasu, K., Hoshikawa, Y., Okabe, T., Hirata, Y. A novel single-stroke path planning algorithm for 3D printers using continuous carbon fiber reinforced thermoplastics. Additive Manufacturing 55, 102816 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYap, T., Tamijani, A.Y., Tehrani, M. Optimum Conversion of Design Optimized Fiber Paths to 3D Printable G-Codes. 37th Technical Conference of the American Society for Composites, ASC 2022, DEStech Publications Inc., 2022.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evan de Werken, N., Hurley, J., Khanbolouki, P., Sarvestani, A.N., Tamijani, A.Y., Tehrani, M. Design considerations and modeling of fiber reinforced 3D printed parts. Composites Part B: Engineering 160, 684\u0026ndash;692 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYap, T., He, Z., Wang, Z., Tamijani, A.Y., Tehrani, M. Experimental investigation and validation of strength-based topology and fiber path optimization in additively manufactured continuous fiber reinforced composites. Additive Manufacturing 89, 104274 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStruzziero, G., Barbezat, M., Skordos, A.A. Consolidation of continuous fibre reinforced composites in additive processes: A review. Additive Manufacturing 48, 102458 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUşun, A., G\u0026uuml;mr\u0026uuml;k, R. The mechanical performance of the 3D printed composites produced with continuous carbon fiber reinforced filaments obtained via melt impregnation. Additive Manufacturing 46, 102112 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, J., Durandet, Y., Huang, X., Sun, G., Ruan, D. Additively manufactured fiber-reinforced composites: A review of mechanical behavior and opportunities. Journal of Materials Science \u0026amp; Technology 119, 219\u0026ndash;244 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuo, M., Tian, X., Shang, J., Zhu, W., Li, D., Qin, Y. Impregnation and interlayer bonding behaviours of 3D-printed continuous carbon-fiber-reinforced poly-ether-ether-ketone composites. Composites Part A: Applied Science and Manufacturing 121, 130\u0026ndash;138 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePu, J., McIlroy, C., Jones, A., Ashcroft, I. Understanding mechanical properties in fused filament fabrication of polyether ether ketone. Additive Manufacturing 37, 101673 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu, H., Sulkis, M., Driver, J., Saade-Castillo, A., Thompson, A., Koo, J.H. Multi-functional ULTEM\u0026trade;1010 composite filaments for additive manufacturing using Fused Filament Fabrication (FFF). Additive Manufacturing 24, 298\u0026ndash;306 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKabir, S.M.F., Mathur, K., Seyam, A.-F.M. A critical review on 3D printed continuous fiber-reinforced composites: History, mechanism, materials and properties. Composite Structures 232, 111476 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYap, T., Heathman, N., Phillips, T., Beaman, J., Tehrani, M. Additive Manufacturing of Polyaryletherketone (PAEK) polymers and their composites. Composites Part B: Engineering 266, 111019 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlok, L.G., Longana, M.L., Yu, H., Woods, B.K.S. An investigation into 3D printing of fibre reinforced thermoplastic composites. Additive Manufacturing 22, 176\u0026ndash;186 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIragi, M., Pascual-Gonz\u0026aacute;lez, C., Esnaola, A., Lopes, C.S., Aretxabaleta, L. Ply and interlaminar behaviours of 3D printed continuous carbon fibre-reinforced thermoplastic laminates; effects of processing conditions and microstructure. Additive Manufacturing 30, 100884 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHeathman, N., Yap, T., Tehrani, M. Hot Isostatic Pressing to Enhance Inter-Laminar Tensile Strength in Additively Manufactured Carbon Fiber-PEEK Parts. 37th Technical Conference of the American Society for Composites, ASC 2020, DEStech Publications Inc., 2020.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartinez, J., Yap, T., Tehrani, M. Effects of Extrusion Rate and Post-Annealing on Mechanical Properties and Printing Quality of Additively Manufactured Carbon Fiber Reinforced Polyetherketoneketone (PEKK) Parts, 37th Technical Conference of the American Society for Composites, ASC 2022, DEStech Publications Inc., 2022.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVaes, D., Van Puyvelde, P. Semi-crystalline feedstock for filament-based 3D printing of polymers. Progress in Polymer Science 118, 101411 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eP\u0026eacute;rez-Mart\u0026iacute;n, H., Mackenzie, P., Baidak, A., \u0026Oacute; Br\u0026aacute;daigh, C.M., Ray, D. Crystallinity studies of PEKK and carbon fibre/PEKK composites: A review. Composites Part B: Engineering 223, 109127 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYi, N., Davies, R., Chaplin, A., McCutchion, P., Ghita, O. Slow and fast crystallising poly aryl ether ketones (PAEKs) in 3D printing: Crystallisation kinetics, morphology, and mechanical properties. Additive Manufacturing 39, 101843 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGao, S.-L., Kim, J.-K. Cooling rate influences in carbon fibre/PEEK composites. Part 1. Crystallinity and interface adhesion. Composites Part A: Applied Science and Manufacturing 31(6), 517\u0026ndash;530 (2000).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAdhikari, S., Durning, C.J., Fish, J., Simon, J.-W., Kumar, S.K. Modeling Thermal Welding of Semicrystalline Polymers. Macromolecules 55(5), 1719\u0026ndash;1725 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChoupin, T., Fayolle, B., R\u0026eacute;gnier, G., Paris, C., Cinquin, J., Brul\u0026eacute;, B. Isothermal crystallization kinetic modeling of poly(etherketoneketone) (PEKK) copolymer. Polymer 111, 73\u0026ndash;82 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ede Macedo, R.Q., Ferreira, R.T.L., Gleadall, A., Ashcroft, I. VOLCO-X: Numerical simulation of material distribution and voids in extrusion additive manufacturing. Additive Manufacturing 40, 101900 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTao, Y., Kong, F., Li, Z., Zhang, J., Zhao, X., Yin, Q., Xing, D., Li, P. A review on voids of 3D printed parts by fused filament fabrication. Journal of Materials Research and Technology 15, 4860\u0026ndash;4879 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePolyzos, E., Ravindranath, S.B., Hemelrijck, D.V., Pyl, L. Analytical and numerical modeling of voids in additively manufactured thermoplastic parts. Additive Manufacturing 48, 102356 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang, D., Zhang, H., Wu, J., McCarthy, E.D. Fibre flow and void formation in 3D printing of short-fibre reinforced thermoplastic composites: An experimental benchmark exercise. Additive Manufacturing 37, 101686 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGhorbani, J., Koirala, P., Shen, Y.-L., Tehrani, M. Eliminating voids and reducing mechanical anisotropy in fused filament fabrication parts by adjusting the filament extrusion rate. Journal of Manufacturing Processes 80, 651\u0026ndash;658 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUeda, M., Kishimoto, S., Yamawaki, M., Matsuzaki, R., Todoroki, A., Hirano, Y., Le Duigou, A. 3D compaction printing of a continuous carbon fiber reinforced thermoplastic. Composites Part A: Applied Science and Manufacturing 137, 105985 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003evan de Werken, N., Koirala, P., Ghorbani, J., Doyle, D., Tehrani, M. Investigating the hot isostatic pressing of an additively manufactured continuous carbon fiber reinforced PEEK composite. Additive Manufacturing 37, 101634 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRietema, M.J. Design of a prototype machine for 3D printing with continious fibre reinforcement. 2015.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, H., Chen, J., Yang, D. Fibre misalignment and breakage in 3D printing of continuous carbon fibre reinforced thermoplastic composites. Additive Manufacturing 38, 101775 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBecker, C., Oberlercher, H., Heim, R.B., Wuzella, G., Faller, L.-M., Riemelmoser, F.O., Nicolay, P., Druesne, F. Experimental Quantification of the Variability of Mechanical Properties in 3D Printed Continuous Fiber Composites. Applied Sciences 11(23), 11315 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, F., Ferraris, E., Ivens, J. Mechanical investigation and microstructure performance of a two-matrix continuous carbon fibre composite fabricated by 3D printing. Journal of Manufacturing Processes 79, 383\u0026ndash;393 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTang, H., Sun, Q., Li, Z., Su, X., Yan, W. Longitudinal compression failure of 3D printed continuous carbon fiber reinforced composites: An experimental and computational study. Composites Part A: Applied Science and Manufacturing 146, 106416 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTerekhina, S., Egorov, S., Tarasova, T., Skornyakov, I., Guillaumat, L., Hattali, M.L. In-nozzle impregnation of continuous textile flax fiber/polyamide 6 composite during FFF process. Composites Part A: Applied Science and Manufacturing 153, 106725 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, F., Wang, G., Ning, F., Zhang, Z. Fiber\u0026ndash;matrix impregnation behavior during additive manufacturing of continuous carbon fiber reinforced polylactic acid composites. Additive Manufacturing 37, 101661 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKuba, D., Matsuzaki, R., Ochi, S., Ogihara, S. 3D printing of composite materials using ultralow-melt-viscosity polymer and continuous carbon fiber. Composites Part C: Open Access 8, 100250 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHeathman, N., Koirala, P., Yap, T., Emami, A., Tehrani, M. In situ consolidation of carbon fiber PAEK via laser-assisted automated fiber placement. Composites Part B: Engineering 249, 110405 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchiel, I., Raps, L., Chadwick, A.R., Schmidt, I., Simone, M., Nowotny, S. An investigation of in-situ AFP process parameters using CF/LM-PAEK. Advanced Manufacturing: Polymer \u0026amp; Composites Science 6(4), 191\u0026ndash;197 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYap, T., Heathman, N., Shirani Bidabadi, B., Motta de Castro, E., Tamijani, A.Y., Asadi, A., Tehrani, M. In-plane properties of an in-situ consolidated automated fiber placement thermoplastic composite. Composites Part A: Applied Science and Manufacturing 188, 108525 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eToray Cetex\u0026reg; TC1225 LMPAEK\u0026trade; Product Data Sheet, 2023. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://bit.ly/3JtGQ0m\u003c/span\u003e\u003cspan address=\"https://bit.ly/3JtGQ0m\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. (Accessed 12/12/2023 2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYap, T., Tamijani, A.Y., Tehrani, M. Aerospace Quality In-situ Consolidated Thermoplastic Composite Structures via Automated Fiber Placement: Effects of Staggering on Part Performance. AIAA SCITECH 2023 Forum.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang, K., Zhang, H., Wu, J., Chen, J., Yang, D. Improved fibre placement in filament-based 3D printing of continuous carbon fibre reinforced thermoplastic composites. Composites Part A: Applied Science and Manufacturing 168, 107454 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAudoit, J., Rivi\u0026egrave;re, L., Dandurand, J., Lonjon, A., Dantras, E., Lacabanne, C. Thermal, mechanical and dielectric behaviour of poly(aryl ether ketone) with low melting temperature. Journal of Thermal Analysis and Calorimetry 135(4), 2147\u0026ndash;2157 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBurgani, T.d.S., Alaie, S., Tehrani, M. Modeling Flexural Failure in Carbon-Fiber-Reinforced Polymer Composites. Journal of Composites Science 6(2), 33 (2022).\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":"","lastPublishedDoi":"10.21203/rs.3.rs-5412244/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5412244/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAdditive manufacturing (AM) offers numerous advantages over standard manufacturing methods, such as design freedom and enabling limited production run components. Using continuous fiber-reinforced polymer composites, polymer AM can now produce end-use components with mechanical properties rivaling metals. In this paper, five-axis continuous fiber material extrusion (ME) is utilized to manufacture specimens from high-performance semi-crystalline low-melt polyaryletherketone\u0026trade; (LM-PAEK\u0026trade;) composite. ASTM standardized testing showed record matrix-dominated and flexural properties for as-printed parts, with low porosity and high crystallinity. Annealing did not change mechanical properties or crystallinity. Additionally, steering radii specimens and a complex geometric bracket were manufactured using the full out-of-plane 3D printing capability of the five-axis equipment; subsequent X-ray computed tomography showed multiple manufacturing defects and voids when printing high-curvature rasters. Results thus pave the way for using LM-PAEK\u0026trade; to replace other high-performance polymers in continuous fiber AM, although designers should take note of fiber steering in critical load-bearing structures.\u003c/p\u003e","manuscriptTitle":"Five-axis material extrusion of high-performance structural parts with continuous carbon fiber-reinforced LM-PAEK","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-26 12:54:16","doi":"10.21203/rs.3.rs-5412244/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":"66c2c56d-bb8e-429e-8733-9ef87c6f7a4a","owner":[],"postedDate":"November 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":40735270,"name":"Physical sciences/Engineering/Aerospace engineering"},{"id":40735271,"name":"Physical sciences/Materials science/Structural materials/Composites"},{"id":40735272,"name":"Physical sciences/Materials science/Structural materials/Mechanical properties"}],"tags":[],"updatedAt":"2025-01-15T05:25:48+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-26 12:54:16","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5412244","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5412244","identity":"rs-5412244","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}