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Soft robots have gained significant interest due to their high flexibility and adaptability to various working conditions. Recent advancements in engineering and innovative materials have enabled the design and production of sophisticated soft robotic systems with enhanced capabilities. This study aims to evaluate the fatigue behavior of bellow-type pneumatic soft actuators fabricated through fused filament fabrication (FFF) using thermoplastic polyurethane (TPU), compared to silicone rubber cast actuators. The actuators were equipped with resistive flex sensors to monitor bending motion, and fatigue tests were performed with cycles of inflation and deflation until failure. Results showed that 3D printed TPU actuators could withstand a significant number of cycles before failure, with an average of 6410 cycles at 3 bar pressure, compared to 3439 cycles at 1 bar pressure for the silicone actuators. The study identified a set of fabrication parameters that positively affect the durability of TPU actuators, providing valuable insights for replicating these results. Additionally, the study established a plausible range of utilization for 3D-printed FFF actuators in terms of the number of cycles they can endure, offering critical data for engineers and designers to make informed decisions about the design and application of these actuators in various practical scenarios. The findings demonstrate the potential of FFF for producing durable, long-lasting pneumatic soft actuators. [ABSTRACT FROM AUTHOR]

As a typical 3D printing process, fused filament fabrication still has disadvantages when operating on manufacturing lines due to the non-uniform textures of the oriented surfaces of the 3D-printed components. This work investigates the effects of structural parameters, i.e., orientations angle, ABS and PLA materials, three different layer thicknesses, three different perimeters, and three different infill rates utilizing a balanced modified Taguchi experimental design and 63 different parametric combinations to characterize the surface roughness parameters: average Ra, mean roughness depth Rz, root mean square Rq, skewness Rsk, and kurtosis Rku. The analysis of the experimental results, i.e., the levels mean values analysis plots and linear residual analysis of variances, showed that the layer thickness strongly influences all surface parameters and interacts considerably with all orientations. In contrast, material type, number of perimeters, and infill rate had insignificant impacts on surface roughness parameters. Finally, the additive linear modelling approach was utilized and validated for proper predictions, making it helpful for surface engineering applications. [ABSTRACT FROM AUTHOR]

As an abundant commodity, coffee production generates significant scraps and by-products, increasing the potential pollution hazards. Circular economy and bioeconomy can help valorize Spent Coffee Grounds (SCGs), e.g., as fillers in polymer-based composites using conventional manufacturing, i.e., injection molding. Large-format additive manufacturing with pellet extruders offers a further option for new applications, reducing costs for the valorization of biomass waste. However, its use in this context remains unexplored, especially for applications with complex geometries or critical overhangs. This work investigates new biomass waste-based materials for large-format additive manufacturing with direct feeding extrusion, fabricating self-supported complex overhang geometries through nonplanar slicing. The thermal, rheological, and mechanical properties of three novel polymer-based pellet compounds with post-industrial SCGs, i.e., injection molding grade polylactic acid/SCGs, recycled low-density polyethylene/SCGs, and high-density polyethylene/SCGs, were herein investigated to evaluate their printability, defining their extrusion temperatures (190 °C and 170 °C). Results showed suitable viscosity ranges (133.6–839.7 Pa∙s) and accurate tensile values comparable with literature, e.g., ~ 1–3% minimum relative standard deviations (polylactic acid/SCGs), or conventional manufacturing, e.g., elastic moduli of 107.4 MPa (recycled low-density polyethylene/SCGs) and 587 MPa (high-density polyethylene/SCGs). Their use with large-format 3D printers was assessed thanks to nonplanar samples with complex overhang geometries, reaching a maximum curvature angle of 32° and fabricating overhangs up to 25° without supports. According to the tests, especially polylactic acid/SCGs, a bio-based compound, and recycled low-density polyethylene/SCGs, a fully recycled material, can be used for large-format 3D printing applications with complex geometries, e.g., furniture, interior, and exhibition design. This work paves the way for new materials for large-format additive manufacturing, reducing the need for 3D printing grade feedstock, cutting costs and consumption from filament processing, and fostering material waste reduction practices. [ABSTRACT FROM AUTHOR]

Highlights Flax fiber has emerged as a promising, eco‐friendly alternative to traditional synthetic reinforcement in polymer composites. However, manufacturing biocomposites using three‐dimensional (3D) printing technology is typically accompanied by significant processing challenges and weak product performance under dynamic loading conditions. This study aims to unlock the potential of 3D‐printed polylactic acid (PLA) by incorporating chemically modified chopped flax fibers and thermoplastic polyurethane elastomer to improve impact strength and processability. To achieve this, we employed the fused deposition modeling (FDM) technique to prepare composite specimens for the study. The crystallization behavior, tensile and impact properties, as well as the fracture behavior of the composites were investigated. The findings suggest that our approach stands out because it not only facilitates the challenging task of 3D printing PLA with fiber additives of high weight fraction and high aspect ratio but also results in a remarkable 120% enhancement in impact strength and an around 31.2% increase in tensile elongation compared to neat PLA, without compromising the elastic modulus. Flax fibers were modified through alkalization and silanization. Alkalization significantly enhanced printing quality. Silanization reduced fiber attrition and doubled the fiber aspect ratio. TPU particles facilitated the 3D printing of biocomposites. For the first time, the hybrid strategy doubled the impact strength of PLA. [ABSTRACT FROM AUTHOR]

High‐performance engineering thermoplastics are important emerging materials, particularly when processed using additive manufacturing technologies. One of the most important among these is polyetherimide, also known as PEI or ULTEM. Using the fused filament fabrication (FFF) additive manufacturing (AM) process to form this material is a good option, but it is difficult to control the properties in some cases due to the very high processing temperature compared with most engineering thermoplastics. One way to "even‐out" the properties is to wrap the specimens in continuous glass or carbon fibers embedded in a thermosetting matrix, as this allows strategic placement and orientation of reinforcement. This also complements the natural structure of the FFF‐manufactured materials, helping to minimize the amount of additional weight that needs to be added to a part. To further knowledge in this area, the present study explored and compared the interlaminar tensile strength of FFF‐processed PEI/ULTEM 9085 specimens and compared them with ones wrapped in carbon fibers with a 2‐part resin matrix. Experiments were performed in accordance with the guidelines given in the ASTM D6415 standard and replicated five times. Variations were introduced in thickness of the specimen and raster angle during the manufacturing process to identify the significant impact of the failure. The results show a fall in interlaminar tensile strength with increasing specimen thickness and a very large effect from natural printing defects in the samples. The carbon fiber wrap decreased the ILTS but made the results far more consistent between experimental runs. This study provides a good, replicated dataset on the performance of raw and fiber‐wrapped FFF‐processed ULTEM 9085 and gives insights into the structural behavior of the material that will be useful for use in design decisions and material selection. Highlights: Polyetherimide, also known as PEI/ULTEM, is a high‐performance engineering thermoplastic.Explored the interlaminar tensile properties (ILTS) of this material using ASTM D6415.Raster angle, thickness, and use of fiber wrap were experimental parameters.Fiber wrap was found to have little effect on strength but made results more consistent.Results are useful for material selection and design decisions using PEI. [ABSTRACT FROM AUTHOR]

This study is centered on the analysis of composite component additive manufacturing, via fused filament fabrication (FFF), comprising of 316L stainless steel particles in a polymer matrix. It examines the impact of several process factors of FFF, including extrusion speed, layer height, and extrusion temperature, on the density and surface roughness with the goal to minimize porosity. The independent and interaction impacts of these parameters were investigated using a central composite design technique. The technique of analysis of variance was utilized to determine the influence of relevant factors. Regression analysis was used to establish statistical models linking the parameters to green density and surface roughness. The green density was enhanced by reducing the layer height from 0.2 to 0.1 μm and decreasing the nozzle speed from 100 to 20 mm min−1. The surface roughness was improved by using a slow printing speed and minimum layer height. The ideal temperature range for producing favorable results in terms of green density and surface roughness during extrusion was found to be between 235 and 240°C. Significant correlations were found between the parameters and the green density and surface roughness. A genetic algorithm was used as an optimisation tool to determine the thresholds that would provide the highest green density and the lowest surface roughness values. The porosity of the samples generated with the optimized settings was evaluated using microtomography scans. The methodology presented here can be applied to composite and standard polymeric filament printing to determine optimal printing parameters. Highlights: Blend of stainless steel 316L and polymer was used for fused filament fabrication.Printing speed and layer height were the dominating for density and roughness.Height 0.2 mm, speed 20 mm s−1, and temperature 239°C resulted 4.73 g cm−3 density and 21.09 μm roughnessMicrotomography revealed porosity of 1.7% in the optimized sample. [ABSTRACT FROM AUTHOR]

Fused filament fabrication (FFF) has become the preferred method for 3D printing of thermoplastic polymer parts due to its cost-effectiveness in comparison with powder- or resin-based 3D printing methods in both machines and materials. It also holds the potential to replace injection molding for small batch production, due to significantly reduced tooling costs, lead time, and the ability to create complex structures. However, the mechanical strength of polymer parts fabricated using this method is significantly lower than those produced using injection molding; this issue is worse in printed polymer composites due to undesirable rheological behaviors of infills during the filament extrusion process. This study investigates the use of an in-process orbiting laser pre-deposition heating technique aimed to enhance the mechanical strength of carbon fiber–reinforced filament in FFF. In this work, the mechanical strength, strain, and fracture behavior are investigated. This innovative technology increases tensile strength from 17.4 to 34.9 MPa at 0.45 W laser power and increases strain from 0.028 to 0.084. Moreover, the laser-treated samples exhibit marked differences in fracture surface characteristics when compared to control samples. The adoption of this approach can provide a solution to the main barrier to the adoption of FFF 3D for engineering and industrial applications. [ABSTRACT FROM AUTHOR]

Polyetheretherketone is a promising material for implants due to its good mechanical properties and excellent biocompatibility. Its accessibility to a wide range of applications is facilitated by the ability to process it with an easy-to-use manufacturing process such as fused filament fabrication. The elimination of disadvantages associated with the manufacturing process, such as a poor surface quality, is a main challenge to deal with. As part of the mass finishing process, centrifugal disc finishing has demonstrated good results in surface optimization, making it a promising candidate for the post-processing of additively manufactured parts. The objective of this study is to identify the key parameters of the centrifugal disc finishing process on the waviness of additively manufactured PEEK specimens, which has not been investigated previously. The waviness of the specimen was investigated by means of confocal laser scanning microscopy (CLSM), while weight loss was additionally tracked. Six parameters were investigated: type, amount and speed of media, use of compound, amount of water and time. Type of media, time and speed were found to significantly influence waviness reduction and weight loss. Surface electron microscopy images demonstrated the additional effects of deburring and corner rounding. Results on previous studies with specimens made of metal showed similar results. Further investigation is required to optimize waviness reduction and polish parts in a second post-processing step. [ABSTRACT FROM AUTHOR]

There is a growing need to address waste generated from Fused Filament Fabrication (FFF) 3D printing activities. This study explores the mechanical recycling of waste polylactic acid (PLA) accumulated from failed 3D printing operations and PLA biocomposite filaments containing nanocellulose fibres. FFF 3D printable filaments were produced via melt mixing and extrusion of virgin PLA containing varying amounts of waste PLA. The chemical, thermal and thermomechanical characterisation of each specimen was evaluated using Fourier‐transform infrared spectroscopy (FTIR), simultaneous thermal analysis (SDT), dynamic mechanical analysis (DMA), and uniaxial tensile analysis (UTA). A desktop FFF 3D printer was used to fabricate UTA and DMA test specimens. The thermal stability of the filament specimens containing waste derived from the failed 3D prints were comparable with that of the commercial filaments. However, a 11% decrease in the onset of thermal degradation is observed for the filament containing waste biocomposites. The specimens containing waste PLA exhibited higher crystallinity and storage modulus. UTA results revealed similar tensile strength and % elongation, except for the specimen containing 50% waste PLA which exhibited a 29% decrease in tensile strength. This work successfully demonstrates mechanical recycling as a viable waste management strategy for waste materials generated during FFF 3D printing. [ABSTRACT FROM AUTHOR]

Due to their low mechanical strength, the limited applications of fused filament fabrication (FFF)-printed products eventually intrigued researchers to overcome this problem through several approaches. Powder addition reinforcement (PAR) has been recognized as the oldest among the proposed techniques. However, several studies have shown the drawbacks of this technique concerning the poor bond between the printed polymer matrix and powder filler, as well as the nozzle clogging that often occurs during the printing process. In this study, a novel powder addition method using equipment that enables powder delivery with a continuous and intermittent flow was conducted. A composite sample was prepared by printing polylactic acid (PLA) filament combined with iron oxide (Fe3O4) powder particles. The results showed that the printed PLA/Fe3O4 samples obtained from processing with intermittent particle flow had better quality compared to those processed by continuous particle flow. However, both the continuous and intermittent powder addition experienced a negative effect due to rapid cooling caused by air exposure during the printing process. Nonetheless, the novel technique proposed in this study could show the ability to avoid nozzle clogging that might occur during the printing of PLA/Fe3O4 composite samples. [ABSTRACT FROM AUTHOR]

Cranioplasty is the procedure that is frequently used to treat deficiencies in the skull bone brought on by skull abnormalities in bone, traumatic skull fractures, bone malignancy, and infections. In surgery, biocompatible materials with unique properties have been utilized. Given the functionality and aesthetic standpoint, the human skull approach for repairing and restoring the abnormalities is hugely challenging. Polymethylmethacrylate (PMMA) cement, based on a dough-like material formed by combining two powdered polymer and liquid monomer components, is considered one of the earliest materials to treat cranial defects. Regarding the development of the latest additive manufacturing technologies, 3D printing has become a promising method for creating cranial implants customized to each patient. This study uses a solid basic medical grade PMMA material as a basis filament for the fused filament fabrication (FFF) process. This paper presents a high-quality model and manufacturing of a left parietal-temporal implant in the human skull based on computed tomography CT images. It evaluates the fitting accuracy and topographical roughness of the PMMA cranial implant. The results proved that the root means square error values for the deviation between the cranial implant's physical model and its planned model are (0.628, 0.833, and 0.650 mm) and implant roughness measurements are (2.5, 2.81, and 3.23 μm). The implemented framework outlined in the present study indicates that the contour continuity between implant-skull overlap, fitting accuracy, implant roughness topography, and the cosmetic outcome achieved entirely satisfactory results. Highlights: Reconstructed the skull defect by using mouldless 3D printing PMMA to manufacture high-quality patient-specific cranial implants directly. A qualitative and quantitative evaluation of implant dimensional accuracy is given and ensure the contour continuity between implant-skull overlap is ensured. Evaluate the cranial implant surface topography. [ABSTRACT FROM AUTHOR]

In recent years, material extrusion-based additive manufacturing, particularly fused filament fabrication (FFF), has gained significant attention due to its versatility and cost-effectiveness in producing complex geometries. This paper presents the characterization of seven novel materials for FFF and twenty-two commercially available filaments in terms of X-ray computed tomography (CT) numbers, as tissue mimicking materials for the realization of 3D printed radiological phantoms. Two technical approaches, by 3D printing of cube samples and by producing cylinders of melted materials, are used for achieving this goal. Results showed that the CT numbers, given in Hounsfield unit (HU), of all the samples depended on the beam kilovoltage (kV). The CT numbers ranged from +411 HU to +3071 HU (at 80 kV), from −422 HU to +3071 HU (at 100 kV), and from −442 HU to +3070 HU (at 120 kV). Several commercial and custom-made filaments demonstrated suitability for substituting soft and hard human tissues, for realization of 3D printed phantoms with FFF in CT imaging. For breast imaging, an anthropomorphic phantom with two filaments could be fabricated using ABS-C (conductive acrylonitrile butadiene styrene) as a substitute for breast adipose tissue, and ASA-A (acrylic styrene acrylonitrile) for glandular breast tissue. [ABSTRACT FROM AUTHOR]

Both the nacre‐like bionic microstructure and the spiral laminated bionic configuration exhibit superior damage‐tolerance characteristics. On the basis of this observation, the design concept of the bionic helical‐interlayer configuration is innovatively integrated into the design of a bionic nacre‐like honeycomb structure. By systematically studying different spiral angles of honeycomb's interlayer stacking forms, their influence on the structural performance is deeply discussed with four‐point bending tests. Mechanical samples are carefully prepared using short carbon fiber reinforced polyamide composites (i.e., PA6‐CF) through conventional fused filament fabrication (FFF) 3D printing technology, where the accuracy and reliability of the designed bio‐inspired samples are ensured. The experimental results reveal significant improvements in bending strength and elastic modulus across various bionic nacre‐like honeycomb spiral structures compared to uniformly overlap configurations. In particular, the SH‐7.5 sample shows a remarkable 35.47% increase in bending strength and a 65.10% increase in elastic modulus over the SH‐11.25 sample. SEM‐based microstructural analyses are carried out to further explore the fracture mode of the carbon fibers, implied the helical configuration adopted in the nacre‐like honeycomb structure enhances the flexural resistant ability of the PA6‐CF composites. The findings above bear important guiding significance and reference value for the design of lightweight and high damage‐tolerance composite structures. Highlights: A novel bio‐inspired structure is implemented to improve the mechanical performance of fused filament fabricated polyamide composites, where the bionic spiral helical configuration is integrated into high‐fracture‐resistance nacre‐like honeycomb structures.Mechanical testing results indicate that a helix angle under 10° results in a significant improvement in the structural performance of flexural strength.Microstructural analysis reveals that the helical configuration enhances the load‐bearing functionality of reinforcing carbon fibers in the printed polyamide composites.FFF 3D printing enables further implementation of the proposed bio‐inspired novel structure for lightweight and damage‐tolerant composite applications with high customization demands. [ABSTRACT FROM AUTHOR]

Polyether-ether-ketone (PEEK) is a recently commonly used high-performance thermoplastic material with high heat resistance, high chemical resistance, high water resistance, and high wear resistance. Polyether-ether-ketone products with complex structures manufactured through the 3D printing process of fused filament fabrication (FFF) are emerging in the medical field. However, similar to other plastics, PEEK materials are also hygroscopic. This may have an impact on 3D printed products. The effect of storage time of filament on 3D printed PEEK products under specific temperature and humidity conditions has not been further explored. This study is mainly to explore the moisture absorption of PEEK filament for different storage time and the effect of moisture absorption on the performance of 3D printed PEEK products. The correlation between storage time and moisture absorption is verified by experiment. It is found that moisture will affect the surface quality of PEEK products. In addition, the mechanical test results show that the increase in the amount of water absorbed leads to the decrease of material properties, such as tensile strength, density, and hardness. Therefore, it is recommended to store unused or leftover PEEK filaments under vacuum drying conditions. For PEEK filaments that are being printed, it should be ensured to replace them every less than 24 h.Article Highlights: PEEK filament absorbed moisture over time, affecting 3D printed product surface quality. Longer storage time correlated with decreased mechanical properties of 3D printed PEEK. Unused PEEK filaments should be stored under vacuum drying conditions. [ABSTRACT FROM AUTHOR]

Short carbon fiber‐reinforced polymer composites are desirable for many additive manufacturing (AM) applications as they are light and structurally strong. The process parameters in fused filament fabrication (FFF) significantly affect the mechanical properties of SFRP parts. In this work, three‐point bending tests are carried out to investigate the flexural behavior of 3D‐printed polyamide 12 carbon fiber (PA12‐CF) specimens. An L18 Taguchi design of experiments with Gray relational analysis is applied to optimize the FFF parameters. It is shown that build orientation has the most influence on flexural properties and the distribution of short fibers has an additional effect. For a rectilinear infill pattern, the maximum flexural strength of the part was realized at the printing speed, layer thickness, and extrusion temperature of 30 mm/s, 0.15 mm, and 270°C, respectively. With these parameters, the flexural strength of the part is 119.9 MPa and the flexural modulus is 3038 MPa. For a concentric infill pattern, the flexural strength of the part is 15.8% higher at 138.8 MPa. The flexural modulus is also higher at 3692 MPa. This study's results contribute toward optimizing FFF parameters to suit the specific flexural loading requirements of an AM part. [ABSTRACT FROM AUTHOR]

In the fused filament fabrication (FFF) based additive manufacturing process, finding optimum printing parameters for achieving the required mechanical properties of the FFF-built part is challenging. In this study, a representative volume element (RVE) based mesoscale approach was developed to describe the influences of printing parameters on the mechanical behaviors of the 3D printed parts. It was shown that the stress-strain curves up to failure obtained from RVE simulations were well verified by experimental tensile test data of printed PLA samples. Then, effective tensile properties of samples manufactured using different raster angles (0°, 45°/−45°, and 90°) and a wide range of layer heights and widths were predicted and correlated with their respective local damage occurrences. The raster angle strongly affected the elastic modulus and tensile strength. The orientation between interlayer voids and loading direction governed local stress distribution, interface failure, and total deformation of FFF samples. An increased layer height and decreased layer width resulted in a more significant fraction of voids between layers and thus lowered stiffness and tensile strength. The introduced RVE model can serve as a simple tool for determining homogenized responses and studying local stress-strain developments and failure of complex printed parts according to the used printing parameters. [ABSTRACT FROM AUTHOR]

This study presented a comprehensive computational fluid dynamics-based model for fused filament fabrication (FFF) three-dimensional (3D) printing multiphase and multiphysics coupling. A model based on the framework of computational fluid dynamics was built, utilizing the front-tracking method for high precision of multiphase material interfaces, a fully resolved simulation at the mesoscale explores the underlying physical mechanism of the self-supported horizontal printing. The study investigated the influence of printing temperature and velocity on the FFF process, exhibiting a certain self-supporting forming ability over a specific range. The results indicated that during the printing of large-span horizontal extension structures, the bridge deck material transitions from initial straight extension to sagging deformation, ultimately adopting a curved shape. The straight extension distance is inversely proportional to the depth of the sagging deformation. Additionally, the study revealed that printing temperature primarily affected the curing time of the molten material, while printing velocity fundamentally affected the relaxation time of both thermal and dynamic characteristics of the material. [ABSTRACT FROM AUTHOR]

The development of multi-material filaments has enabled fused filament fabrication-based additive manufacturing to address demand for high-performance lightweight multifunctional components. In this study, polylactic acid (PLA) and acrylonitrile butadiene styrene based filaments with metallic reinforcements of magnetic iron (MI), stainless steel (SS), bronze (Br), copper (Cu), Bismuth (Bi), and Tungsten (W) were investigated to elucidate their complex processing–structure–property relationships. The microstructure of 3D-printed materials were characterized by microscopy and analyzed to determine the metal cross-sectional area percentage and the relationship between metal reinforcement, the polymer matrix, and porosity. Compression testing was conducted in directions parallel and perpendicular to the build direction in order to evaluate the effect of orientation and metal reinforcement on the mechanical properties. 3D-printed specimens experienced either fracture through print layers or layer-wise interfacial rupture for loads applied perpendicular and parallel to the print layers, respectively. A dependence of yield strength on loading orientation was observed for Br-PLA, Cu-PLA, SS-PLA, Bi-ABS, and W-ABS; however, MI-PLA and pure ABS specimens did not exhibit this sensitivity. Metal reinforcement also influenced the magnitude of compressive yield strength, with MI-PLA and SS-PLA demonstrating increased strength over Br-PLA and Cu-PLA, while ABS demonstrated increased strength over Bi-ABS and W-ABS. These results demonstrate the importance of considering orientation in printing and applications, the trade-off between various metallic reinforcements for added multifunctionality, and the potential of these tailored polymer composites for novel 3D-printed structures. [ABSTRACT FROM AUTHOR]

This systematic review interrogates the literature to understand what is known about the environmental sustainability of fused filament fabrication, FFF (also known as fused deposition modeling, FDM), based on life cycle assessment (LCA) results. Since substantial energy demand is systematically addressed as one of the main reasons for ecological damage in FFF, mitigation strategies are often based on reducing the printing time (for example, adopting thicker layers) or the embodied energy per part (e.g., by nesting, which means by printing multiple parts in the same job). A key parameter is the infill degree, which can be adjusted to the application requirements while saving printing time/energy and feedstock material. The adoption of electricity from renewable resources is also expected to boost the sustainability of distributed manufacturing through FFF. Meanwhile, bio-based and recycled materials are being investigated as less impactful alternatives to conventional fossil fuel-based thermoplastic filaments. [ABSTRACT FROM AUTHOR]

The present work reports the fabrication via FFF-3D printing of 3- and 8-YSZ electrolytes, which are considered the current state-of-the-art of electrolyte materials for high temperature fuel cells (i.e., SOFCs), using filaments with ceramic loadings in the 65 to 75 wt% range. Filaments, green bodies and sintered specimens have been produced and fully characterised using thermal, structural, morphological, rheological and electrochemical techniques. The 3D printed electrolytes exhibit chemical stability under the debinding and sintering conditions, without significant microstructural changes when compared to conventional press and sinter processing and very high relative densities, compatible with SOFC operation, i.e. > 95%. The conductivity of the 3D printed electrolytes was 0.05 and ≈ 0.1 S/cm at 1000 °C, for 3- and 8-YSZ respectively, which is very close to the values typically reported for conventionally processed zirconia electrolytes. These results confirm the potential application of FFF-3D printing technology towards the production of a new generation of electrochemical devices for energy production, such as SOFCs, with larger volumetric and surface energy densities and without their current geometrical limitations. [ABSTRACT FROM AUTHOR]

The excellent tribological properties of copper are well known, therefore it is commonly used in components whose tribological characteristics have a high impact. Thanks to the characteristics of Additive Manufacturing it is possible to manufacture parts incorporating copper particles. However, the main mechanical studies are related to performance under tensile-compression or bending conditions and the tribological properties remain understudied and this means that there is no knowledge of the possible performance of parts obtained using additive techniques with these particles. For this reason, this article proposes to carry out a study on a polymeric Additive Manufacturing process, specifically, Fused Filament Manufacturing, which is the most widely used process at present and where it is possible to obtain thermoplastic matrix filaments with different types of reinforcements. In this case, a reinforcement of metallic nature will be chosen, such as copper particles, where the properties of this material will be exploited. The aim is to find out how the basic manufacturing parameters, layer thickness and temperature, influence the tribological behaviour of the parts obtained with this process. [ABSTRACT FROM AUTHOR]

Fusion-based material extrusion additive manufacturing, commonly known as fused filament fabrication (FFF), is a layer-by-layer manufacturing process known for creating custom components, specializing in complex geometries, with applications in the aerospace, automotive, medical, as well as many other industries. Due to the critical nature of these industries, it is imperative to understand the relationship between the AM material in question, the nature of the resultant damage, and the impact of these two parameters on the future performance of the component. The purpose of this study is to investigate the relationship between low-velocity impact and the resultant damage in common functional FFF materials and to develop methods of visualizing that damage using ultrasonic nondestructive evaluation. Coupons of a nylon feedstock infused with and without 10% chopped carbon fiber were fabricated using an Essentium HSE printer and impacted at various energies. The extent of the damage was visualized using ultrasonic testing (UT), in which significant internal cracking was observed. Four-point bend testing was utilized to compare behavior of the material prior to impact at a lower impact energy (3J), and a higher impact energy causing visual fracture (7J). X-ray CT was also performed on two samples to validate UT findings. [ABSTRACT FROM AUTHOR]

This review aims to provide an overview of sustainable approaches that can be incorporated into well‐known procedures for the development of materials, pre‐ and post‐treatments, modifications, and applications of 3D‐printed objects, especially for fused filament fabrication (FFF). Different examples of conductive and non‐conductive bespoke filaments using renewable biopolymers, bioplasticizers, and recycled materials are presented and discussed. The main final characteristics of the polymeric materials achieved according to the feedstock, preparation, extrusion, and treatments are also covered. In addition to recycling and remanufacturing, this review also explores other alternative approaches that can be adopted to enhance the sustainability of methods, aiming to produce efficient and environmentally friendly 3D printed products. Adjusting printing parameters and miniaturizing systems are also highlighted in this regard. All these recommended strategies are employed to minimize environmental damage, while also enabling the production of high‐quality, economical materials and 3D printed systems. These efforts align with the principles of Green Chemistry, Sustainable Development Goals (SDGs), 3Rs (Reduce, Reuse, Recycle), and Circular Economy concepts. [ABSTRACT FROM AUTHOR]

Additively manufactured polymer structures often exhibit strong anisotropies due to their layered composition. Although existing methods in additive manufacturing (AM) for improving the mechanical properties are available, they usually do not eliminate the high degree of structural anisotropy. Existing methods for continuous fiber (cF) reinforcement in AM can significantly increase the mechanical properties in the strand direction, but often do not improve the interlaminar strength between the layers. In addition, it is mostly not possible to deposit cFs three-dimensionally and curved (variable–axial) and, thus, in a path that is suitable for the load case requirements. There is a need for AM methods and design approaches that enable cF reinforcements in a variable–axial way, independently of the AM mounting direction. Therefore, a novel two-stage method is proposed in which the process steps of AM and cF integration are decoupled from each other. This study presents the development and validation of the method. It was first investigated at the specimen level, where a significant improvement in the mechanical properties was achieved compared to unreinforced polymer structures. The Young's modulus and tensile strength were increased by factors of 9.1 and 2.7, respectively. In addition, the design guidelines were derived based on sample structures, and the feasibility of the method was demonstrated on complex cantilevers. [ABSTRACT FROM AUTHOR]

Abstract 3D printing technologies such as fused filament fabrication (FFF) offer great opportunities to enable the fabrication of complex geometries without access to a workshop or knowledge of machining. By adding filler materials to the raw filaments used for FFF, the material properties of the plastic can be adapted. With the addition of neutron absorbing particles, filaments can be created that enable 3D printing of neutron shielding with arbitrary geometry. Two materials for FFF are presented with different mixing ratios of hexagonal Boron nitride (h-BN) and Polylactic acid (PLA). BNPLA25 with 25 %wt h-BN and BNPLA35 with 35 %wt h-BN are compared to the commercially available Addbor N25 material. To qualify the applicability of BNPLA25 and BNPLA35 as shielding material for neutron instrumentation, such as neutron imaging, we investigated the overall neutron attenuation, the influence of non-optimized print settings, as well as characterized the incoherent neutron scattering and the microstructure using neutron imaging, and time-of-flight small-angle-neutron-scattering. Finally, the tensile strength of the material was determined in standardized tensile tests. The measured neutron attenuation shows excellent agreement with analytical calculations, thus validating both the material composition and the calculation method. Approximately 6 mm (8 mm) BNPLA35 are needed for $$1\times 10^{-3}$$ 1 × 10 - 3 transmission of a cold (thermal) neutron beam. Lack of extrusion due to suboptimal print settings can be compensated by increased thickness, clearly visible defects can be mitigated by 11–18% increase in thickness. Incoherent scattering is shown to be strongly reduced compared to pure PLA. The tensile strength of the material is shown not to be impacted by the h-BN filler. The good agreement between the measured attenuation and calculation, combined with the adoption of safety factor enables the quick and easy development as well as the performance estimation of shielding components. BNPLA is uniquely suited for 3D printing neutron shielding because of the combination of non-abrasive h-BN particles in standard PLA, which results in a filament that can be printed with almost any off-the-shelf printer and virtually no prior experience in 3D printing. This mitigates the slightly lower attenuation observed as compared to filaments containing $${\hbox {B}_{4}}\hbox {C}$$ B 4 C , which is highly abrasive and requires extensive additive manufacturing experience.

Abstract This study presented a comprehensive computational fluid dynamics-based model for fused filament fabrication (FFF) three-dimensional (3D) printing multiphase and multiphysics coupling. A model based on the framework of computational fluid dynamics was built, utilizing the front-tracking method for high precision of multiphase material interfaces, a fully resolved simulation at the mesoscale explores the underlying physical mechanism of the self-supported horizontal printing. The study investigated the influence of printing temperature and velocity on the FFF process, exhibiting a certain self-supporting forming ability over a specific range. The results indicated that during the printing of large-span horizontal extension structures, the bridge deck material transitions from initial straight extension to sagging deformation, ultimately adopting a curved shape. The straight extension distance is inversely proportional to the depth of the sagging deformation. Additionally, the study revealed that printing temperature primarily affected the curing time of the molten material, while printing velocity fundamentally affected the relaxation time of both thermal and dynamic characteristics of the material.

Abstract This work investigates the viability of discerning the raster pattern of additively manufactured components using high frequency ultrasonic nondestructive testing. Test coupons were fabricated from poly cyclohexylenedimethylene terephthalate glycol using the fused filament fabrication process, in which layers were deposited at various predetermined raster angles. Each printed part was scanned using spherically focused, high-resolution, ultrasonic transducers of various peak frequencies between 7.5 and 15 MHz. From the captured waveform data, images are extracted to observe the raster pattern in a layer-by-layer manner, with the results from the 10 MHz element yielding the best performance. An in-house MATLAB script was developed to analyze the transducer signal to investigate C-scan images at various depths throughout the component. From the resulting C-scan images, one can consistently identify the proper raster orientation within 2°–4° in each of the first 10 deposited layers, with the accuracy decreasing as a function of depth into the component. Due to signal attenuation, there is insufficient data at depths beyond the 11th and 12th layer, to properly analyze the present data sets accurately. Validation was performed using X-ray computed tomography scans to demonstrate the accuracy of the ultrasonic inspection method.

Understanding the external and internal factors during an additive manufacturing (AM) process is crucial, as they can significantly affect the final product's performance. Efforts have been made to unwind the product, process, property, and performance (PPPP) relationships. The conventional experimental approaches can lead to boundless runs, resulting in exorbitant costs for research and development. Hence, developing, adapting, and validating numerical models is essential to achieving the desired performance of 3D-printed products with lesser resource utilization. In this study, numerical and experimental techniques were used to perform the PPPP relationship assessment on material extrusion 3D-printed parts. Three infill designs (rectangular, triangular, and hexagonal), with layer heights (0.1 mm, 0.125 mm, and 0.2 mm), and three different materials (carbon fiber-reinforced polyamide-6 (PA6-CF), polyamide-6 (PA6), and acrylonitrile butadiene styrene (ABS)), were selected for the investigation. Taguchi's design of experiments (DOE) method was used to limit the number of numerical simulations and experimental runs. A thermomechanical numerical model was utilized to perform the material extrusion process simulations and mechanical performance prediction of the specimens. Subsequently, the samples were 3D-printed and tested mechanically to validate the numerical simulation results. The dimensional, distortion, and mechanical analysis performed on numerical simulation results agreed well with the experimental observations.

The expansive utility of polymeric 3D-printing technologies and demand for high- performance lightweight structures has prompted the emergence of various carbon-reinforced polymer composite filaments. However, detailed characterization of the processing–microstructure–property relationships of these materials is still required to realize their full potential. In this study, acrylonitrile butadiene styrene (ABS) and two carbon-reinforced ABS variants, with either carbon nanotubes (CNT) or 5 wt.% chopped carbon fiber (CF), were designed in a bio-inspired honeycomb geometry. These structures were manufactured by fused filament fabrication (FFF) and investigated across a range of layer thicknesses and hexagonal (hex) sizes. Microscopy of material cross-sections was conducted to evaluate the relationship between print parameters and porosity. Analyses determined a trend of reduced porosity with lower print-layer heights and hex sizes compared to larger print-layer heights and hex sizes. Mechanical properties were evaluated through compression testing, with ABS specimens achieving higher compressive yield strength, while CNT-ABS achieved higher ultimate compressive strength due to the reduction in porosity and subsequent strengthening. A trend of decreasing strength with increasing hex size across all materials was supported by the negative correlation between porosity and increasing print-layer height and hex size. We elucidated the potential of honeycomb ABS, CNT-ABS, and ABS-5wt.% CF polymer composites for novel 3D-printed structures. These studies were supported by the development of a predictive classification and regression supervised machine learning model with 0.92 accuracy and a 0.96 coefficient of determination to help inform and guide design for targeted performance. [ABSTRACT FROM AUTHOR]

3D printing of thermoplastics through local melting and deposition via material extrusion additive manufacturing provides a simple route to the near net‐shape manufacture of complex objects. However, the mechanical properties resulting from these 3D printed structures tend to be inferior when compared to traditionally manufactured thermoplastics. These unfavorable characteristics are generally attributed to the structure of the interface between printed roads. Here, we illustrate how the molecular mass distribution for a model thermoplastic, poly(methyl methacrylate) (PMMA), can be tuned to enhance the Young's modulus of 3D printed plastics. Engineering the molecular mass distribution alters the entanglement density, which controls the strength of the PMMA in the solid state and the chain diffusion in the melt. Increasing the low molecular mass tail increases Young's modulus and ultimate tensile strength of the printed parts. These changes in mechanical properties are comparable to more complex routes previously reported involving new chemistry or nanoparticles to enhance the mechanical performance of 3D printed thermoplastics. Controlling the molecular mass distribution provides a simple route to improve the performance in 3D printing of thermoplastics that can be as effective as more complex approaches. [ABSTRACT FROM AUTHOR]

Solid composites used in material extrusion additive manufacturing have experienced considerable expansion over the past 5 years, incorporating functional properties into 3D‐printed objects. This paper presents a systematic review that aims to: (I) analyze the current state of development in the field; (II) quantify and categorize the adopted polymeric matrices, reinforcing materials, feedstock shapes, characterization strategies, and extrusion mechanisms; and (III) identify the applications, limitations, and trends for future research. The PRISMA statement was followed and the databases Scopus, Web of Science, and PubMed were consulted. Among the 116 included studies, the use of customized filaments surpassed the commercially available ones, with particulate matter being the most common form of filler when melt‐mixed with the polymer. Polyamide is the most widely adopted matrix (30.3%), followed by PLA (22.0%) and ABS (17.4%). In terms of reinforcements, carbon fiber (32.4%), glass fiber (12.5%), and ceramics (12.5%) compose the podium as the most frequently used, with nanofillers receiving increasing attention. In the conducted analysis, no standardized protocols were identified that clearly encompassed the entire process from feedstock formulation to technical prototype fabrication. At last, recycling, exploration of biodegradable materials, and 4D printing were identified as the main opportunities for future research. Highlights: Reinforced polymers enable the enhancement of properties for 3D‐printed parts.Composite feedstock is usually formulated and mixed before printing.3D printers with filament‐ or screw‐based extrusion mechanisms have been used.Mechanical and morphological analyses are common in material characterization.No identified applications were employed in real‐world scenarios. [ABSTRACT FROM AUTHOR]

In recent years, the number of studies focusing on the additive manufacturing has increased seriously to elucidate the critical points such as physical, chemical, and mechanical properties. Contrary to common trends and for the first time in the literature, this experimental endeavor aims to comprehend the combined impact of reinforcement type and heat treatment on the wear features of additively manufactured polyamide 6 (PA6) composites. As reinforcement materials, glass, and carbon fibers were utilized and all samples were created through the fused filament fabrication. Half of the samples were subjected to annealing treatment after the main production, and characterization works were performed using a fused emission scanning electron microscope, differential scanning calorimetry, and dynamic mechanic analysis. From the outcomes, it is seen that heat treatment has a positive effect on the hardness, and wear resistance of the composites. Besides, glass fiber‐reinforced samples display lower friction coefficient and lower volume loss results than other samples. For all samples, secondary annealing causes a positive impact on wear endurance in most cases. On the other side, the wear mechanism of the tested samples changes with the test force level and reinforcement type. At lower test forces, abrasive wear‐induced debris parts are detected on the deformed surfaces of PA6 and carbon‐added samples, but this case is opposite for the highest force of 40 N. Highlights: Additive manufacturing was underlined as a promising way to create polymer composites with high dimensional accuracy.The combined effect of secondary annealing and reinforcement type on the wear resistance of 3D‐printed PA6 composites was examined for the first time in the literature.Carbon and glass fibers were compared to explore their effect on friction coefficient and wear behavior of polymer composite samples produced via FFF technology.Hardness and surface roughness measurements were used to comprehend the dry sliding wear results.Depending on the increasing test force levels and reinforcement type, deformation, and abrasion mechanisms were analyzed. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is often used to create designs inspired by topology optimization and biological structures, yielding unique cross-sectional geometries spanning across scales. However, manufacturing defects intrinsic to AM can affect material properties, limiting the applicability of a uniform material model across diverse cross-sections. To examine this phenomenon, this paper explores the influence of specimen size and layer height on the compressive modulus of polycarbonate (PC) and thermoplastic polyurethane (TPU) specimens fabricated using fused filament fabrication (FFF). Micro-computed tomography imaging and compression testing were conducted on the printed samples. The results indicate that while variations in the modulus were statistically significant due to both layer height and size of the specimen in TPU, variations in PC were only statistically significant due to layer height. The highest elastic modulus was observed at a 0.2 mm layer height for both materials across different sizes. These findings offer valuable insights into design components for FFF, emphasizing the importance of considering mechanical property variations due to feature size, especially in TPU. Furthermore, locations with a higher probability of failure are recommended to be printed closer to the print bed, especially for TPU, because of the lower void volume fraction observed near the heated print bed. [ABSTRACT FROM AUTHOR]

Ultrasonic guided waves (UGWs) based structural health monitoring (SHM) systems are widely used in several engineering fields for real‐time damage detection, since they are particularly sensitive to material local changes, induced, i.e., by a damage. This paper aims to investigate on the use of SHM systems in additively manufactured laminate. Specifically, a flat panel made of XSTRAND GF30‐PA6 material, fabricated by Ultimaker S5 fused filament fabrication (FFF) based 3D printer, is used as a case study. Signals recorded by a piezoelectrics (PZTs) array are analyzed to highlight the dispersive behavior of symmetric, S0, mode along different measurement paths in the excitation frequency range of 100–300 kHz. [ABSTRACT FROM AUTHOR]

Taking crustacean organisms in nature as prototypes helps improve the design of protective gears. Drawing inspiration from the high-damage-tolerance helical-structured cuticle of the American crayfish, we conduct an optimization of processing parameters for Fused Filament Fabrication 3D printing products. Various values of in-plane raster angle and interlayer thickness are employed to replicate the damage-resistant feature mimicked from nature. The effect of flexural resistances on 3D-printed three-point bending specimens is being investigated using a combination of four helical printing raster angles at four different layer thicknesses. Acrylonitrile-butadiene-styrene (ABS) and glass fiber-reinforced ABS (ABS-GF) are employed as material models. A Dino-lite handheld microscope and a Keyence VHX-7000 optical microscope are used to characterize the microstructure of the samples' fracture resistance after the three-point bending test. Explanations of the mechanism of fracture resistance for helical structures are given. The results show that the specimen with a layer thickness of 0.04 mm and a spiral angle of 30° has the highest bending strength and bending elastic modulus among all the tested specimens. When compared with the layer thickness of 0.16 mm, the bending strength and bending elastic modulus of the ABS helix specimen with a layer thickness of 0.04 mm are increased by 6.45% and 2.67%, and those of the ABS-GF helix specimen are increased by 21.21% and 10.03%, respectively. The microstructural observation of the samples reveals that the spiral specimens with a helix angle of 11.25° have a greater displacement of crack propagation to resist the damage extending inside when resisting fracture. Our bio-inspired study presents an alternative approach to comprehensively optimize FFF printing parameters for enhanced mechanical performance. [ABSTRACT FROM AUTHOR]

Fused Filament Fabrication (FFF) is a 3D (three-dimensional) printing technology that allows the production of polymers with a wide range of infill densities and unlimited geometric variations. Because of this flexibility, mechanical properties can be optimized by tuning printing parameters. However, the energy consumption during fabrication varies significantly for different printing settings. In the present study, both maximum fracture force and minimum energy consumption of 3D printed PLA (Polylactic Acid) are achieved together by optimizing the printing parameters using CPA (Cyclical Parthenogenesis Algorithm) optimization algorithm. Firstly, a quasi-static penetration test is performed to measure the maximum fracture force. The energy consumption of each specimen is also calculated. Then, maximum fracture force and energy consumption are modeled and integrated into the optimization algorithm. As a result, the three most convenient parameter levels are 84%, 6.83 mm, and 0.19 mm for infill ratio, specimen thickness, and layer height, respectively. While high infill ratio values and specimen thickness increase mechanical performance, these parameter levels are disadvantageous for energy consumption. As a result of optimization, parameters that provide balanced strength and energy consumption were obtained. Fracture force and energy consumption are 1829.87 N and 134.56 W, respectively for the validation experiment of the optimal solution. [ABSTRACT FROM AUTHOR]

The objective of this study is to design a biomimetic hybrid structure inspired by nacre, and conch shells and compare how the compressive characteristics change when key geometric design parameters are varied. Nacre, also known as mother of pearl, has a host of traits, suitable for survival, like its stiffness and strength. Conch, which is a common name for a number of sea snails, possesses a unique cross-lamellar structure which has a tough outer layer to resist penetration from the sharp-toothed attacks of predators, and a nacreous inner layer which can dissipate energy. A novel nacre–conch–nacre inspired sandwich core structure is designed and fabricated with fuse filament fabrication using acrylonitrile styrene acrylate filament according to the ASTM C365 standard for the flatwise compression test of sandwich core structures. Three key design parameters, namely the wall thickness, the thickness between two nacre walls, and the angle of conch were selected and varied to form nine different iterations of this design. An Abaqus finite element analysis was validated by experimental testing using an Instron 8801 servo-hydraulic universal testing machine. The results showed that conch-inspired structures' compression properties depend on wall thickness and angle. The sample with 2 mm wall thickness and 45° conch angle had the highest compressive strength of 3.62 MPa, while the sample with 1 mm wall thickness and 50° conch angle had the lowest at 2.09 MPa. These findings suggest this structure could be used in lightweight armor, car, and aerospace parts. [ABSTRACT FROM AUTHOR]