Search Results (99)

Thermoplastic in situ Automated Fiber Placement (AFP) is an additive manufacturing method currently investigated for its suitability for the production of aerospace-grade composite structures. A considerable expense in this process is the manufacturing and preparation of a mold in which a composite part can be manufactured. One approach to lowering these costs is the use of a 3D-printable thermoplastic mold. However, AFP lay-up on a 3D-printed mold differs from the usage of a traditional metallic mold in various aspects. Most notable is a reduced stiffness of the mold, a lower thermal conductivity of the mold, and the need for varied process parameters of the AFP process. This study focuses on the investigation of the difference in mechanical and morphological characteristics of laminates produced on metallic and polymeric molds. To this end, the tensile strength and the interlaminar shear strength of laminates manufactured on each substrate were measured and compared. Additionally, morphological analysis using scanning electron microscopy and differential scanning calorimetry was performed to compare the crystallinity in laminates. No statistically significant difference in mechanical or morphological properties was found. Thus, thermoplastics were shown to be a suitable material for non-heated molds to manufacture in situ AFP composites. Full article

Nowadays, Fused Filament Fabrication (FFF) 3D printing offers promising opportunities for the customized manufacturing of ankle–foot orthoses (AFOs) targeted towards rehabilitation purposes. Polypropylene (PP) represents an ideal candidate in orthotic applications due to its light weight and superior mechanical properties, offering an excellent balance between flexibility, chemical resistance, biocompatibility, and long-term durability. However, Additive Manufacturing (AM) of AFOs based on PP remains a major challenge due to its limited bed adhesion and high shrinkage, especially for making large parts such as AFOs. The primary innovation of the present study lies in the optimization of FFF 3D printing parameters for the fabrication of functional, patient-specific orthoses using PP, a material still underutilized in the AM of medical devices. Firstly, a thorough thermomechanical characterization was conducted, allowing the implementation of a (thermo-)elastic material model for the used PP filament. Thereafter, a Taguchi design of experiments (DOE) was established to study the influence of several printing parameters (extrusion temperature, printing speed, layer thickness, infill density, infill pattern, and part orientation) on the mechanical properties of 3D-printed specimens. Three-point bending tests were conducted to evaluate the strength and stiffness of the samples, while additional tensile tests were performed on the 3D-printed orthoses using a home-made innovative device to validate the optimal configurations. The results showed that the maximum flexural modulus of 3D-printed specimens was achieved when the printing speed was around 50 mm/s. The most significant parameter for mechanical performance and reduction in printing time was shown to be infill density, contributing 73.2% to maximum stress and 75.2% to Interlaminar Shear Strength (ILSS). Finally, the applicability of the finite element method (FEM) to simulate the FFF process-induced deflections, part distortion (warpage), and residual stresses in 3D-printed orthoses was investigated using a numerical simulation tool (Digimat-AM^®). The combination of Taguchi DOE with Digimat-AM for polypropylene AFOs highlighted that the 90° orientation appeared to be the most suitable configuration, as it minimizes deformation and von Mises stress, ensuring improved quality and robustness of the printed orthoses. The findings from this study contribute by providing a reliable method for printing PP parts with improved mechanical performance, thereby opening new opportunities for its use in medical-grade additive manufacturing. Full article

In recent times, fiber reinforced polymer composite materials have become more popular due to their remarkable features such as high specific strength, high stiffness and durability. Particularly, Carbon Fiber Reinforced Polymer (CFRP) composites are one of the most prominent materials used in the field of transportation and building engineering, replacing conventional materials due to their attractive properties as mentioned. In this work, a CFRP laminate is fabricated with carbon fiber mats and epoxy by a hand layup technique. Alumina (Al₂O₃) micro particles are used as a filler material, mixed with epoxy at different weight fractions of 0% to 4% during the fabrication of CFRP laminates. The important objective of the study is to investigate the influence of alumina micro particles on the mechanical performance of the laminates through characterization for various physical and mechanical properties. It is revealed from the results of study that the mass density of the laminates steadily increased with the quantity of alumina micro particles added and subsequently, the porosity of the laminates is reduced significantly. The SEM micrograph confirmed the constituents of the laminate and uniform distribution of Al₂O₃ micro particles with no significant agglomeration. The hardness of the CFRP laminates increased significantly for about 60% with an increase in weight % of Al₂O₃ from 0% to 4%, whereas the water gain % gradually drops from 0 to 2%, after which a substantial rise is observed for 3 to 4%. The improved interlocking due to the addition of filler material reduced the voids in the interfaces and thereby resist the absorption of water and in turn reduced the plasticity of the resin too. Tensile, flexural and inter-laminar shear strengths of the CFRP laminate were improved appreciably with the addition of alumina particles through extended grain boundary and enhanced interfacial bonding between the fibers, epoxy and alumina particles, except at 1 and 3 wt.% of Al₂O₃, which may be due to the pooling of alumina particles within the matrix. Inclusion of hard alumina particles resulted in a significant drop in impact strength due to appreciable reduction in softness of the core region of the laminates. Full article

The effect of the interaction between silica (nS) and hydroxyapatite (nHap) nanomaterials on the characteristics of unidirectional glass-fiber-reinforced epoxy (GF/Ep) composite systems is investigated in this work. The goal of the study is to use these nanofillers to improve the microstructure and mechanical characteristics. Pultrusion was used to produce hybrid nanocomposites while keeping the GF loading at a consistent 75% by weight. The hybrid nanocomposites were made with a total filler loading of 6 wt.%, including nHap, and a nS loading ranging from 2 to 4 wt.%. The mechanical performance of the composite was greatly improved by the use of these nanofillers. Compared to neat GF/Ep, hybrid nanocomposites with 6 wt.% combined fillers exhibited increased hardness (14%), tensile strength (25%), interlaminar shear strength (21.3%), and flexural strength (33%). These improvements are attributed to efficient filler dispersion, enhanced fiber-matrix adhesion, and crack propagation resistance. Incorporating 4 wt.% nS alone improved hardness (6%), tensile strength (9%), tensile modulus (21%), interlaminar shear strength (11.4%), flexural strength (12%), and flexural modulus (14%). FTIR analysis indicated Si-O-Si network formation and increased hydrogen bonding, supporting enhanced interfacial interactions. Ultraviolet reflectance measurements showed increased UV reflectivity with nS, especially in hybrid systems, due to synergistic effects. Impact strength also improved, with a notable 11.6% increase observed in the hybrid nanocomposite. Scanning and transmission electron microscopy confirmed that the nanofillers act as secondary reinforcements within the matrix. These hybrid nanocomposites present a promising material choice for various industries, including marine structural applications and automotive components. Full article

The limited mechanical properties of composite materials, including stiffness, strength, and biocompatibility, restrict their effectiveness in biomedical applications. This research enhanced the mechanical properties and biocompatibility of polylactic acid and carbon fiber-reinforced composites (PLA/CFRCs) by incorporating multi-walled carbon nanotube (MWCNT) fillers. The methodology involved synthesizing MWCNTs and integrating them into PLA/CFRC laminates using fusion-blending, dispersion, and interlaminar spray-coating. Raman spectroscopy confirmed the presence of MWCNTs, with characteristic D and G band peaks and an I_D/I_G of 1.44 ± 0.089. SEM revealed MWCNTs in the PLA/CFRC matrix and allowed size determination, with an outer diameter range of 125–150 nm and a length of 14,407 ± 2869 nm. FTIR identified interactions between the matrix and the MWCNTs, evidenced by band shifts. TGA/DSC analysis showed thermal stability above 338 °C for all composites. The tensile tests revealed that all composites had values greater than 19 GPa for the elastic modulus and 232 MPa for the ultimate strength. Cytotoxicity assays confirmed biocompatibility, and all samples maintained a cell growth rate greater than 80%. This study highlighted the potential of nanotechnology to optimize the mechanical behavior of polymer-based composites, expanding their applicability in biomedical fields. Full article

Carbon fiber-reinforced composite stringers, which support aircraft skins in resisting tensile, compressive, and shear loads, are widely used in aircraft structures. These composite structures play a crucial role in enhancing the performance and safety of the structural integration of aircrafts. To better understand the load-bearing capacity of composite stringer structures, this study developed a novel model to study the complex failure and load transmission behavior of T800/3900S-2B fiber-reinforced composite skin-stringer structures under compressive loading. Compression strength tests were conducted on a composite stringer/skin structure, and a three-dimensional FEM was developed using Abaqus/Standard 2022. The model incorporated the modified 3D Hashin initiation criteria and Tserpes degradation law through a UMAT subroutine, which can effectively capture the in-plane ply failure and interlaminar damage. The results revealed a high degree of similarity between the load–displacement curves and failure modes (i.e., matrix compressive cracking, fiber compressive failure, and fiber–matrix shear-out failure) obtained from the simulations and those from the experiments. This study provides an efficient and accurate model to simulate the failure and load transfer of composite skin-stringer structures, offering significant advancements in understanding and predicting the behavior of these critical components. Full article

Two types of T800 grade carbon fibers, produced using distinct spinning processes, were utilized to fabricate thermoplastic prepregs via the hot melt method. These prepregs were subsequently employed to produce thermoplastic composites. A universal testing machine was used to assess the tensile, bending, and interlaminar shear properties of the composites, evaluating the impact of the two different spinning processes on their mechanical characteristics. The experimental results indicate that the dry spray wet spinning carbon fiber (T800-DJWS) exhibits a smoother surface, more regular cross-section, and more uniform distribution compared to the wet spinning carbon fiber (T800-WS), enhancing the prepreg preparation via the hot melt method. The T800-DJWS/PAEK composite demonstrates a tensile strength that is 706 MPa higher than the T800-WS/PAEK composite, while the latter exhibits a bending modulus 31 GPa higher than the former. Full article

This article is a numerical and experimental study of the mechanical properties of different glass, flax and hybrid composites. By utilizing hybrid composites consisting of natural fibers, the aim is to eventually reduce the percentage usage of synthetic or man-made fibers in composites and obtain similar levels of mechanical properties that are offered by composites using synthetic fibers. This in turn would lead to greener composites being utilized. The advantage of which would be the presence of similar mechanical properties as those of composites made from synthetic fibers along with a reduction in the overall weight of components, leading to much more eco-friendly vehicles. Finite element simulations (FEM) of mechanical properties were performed using ANSYS. The FEM simulations and analysis were performed using standards as required. Subsequently, actual beams/frames with a defined geometry were fabricated for applications in automotive body construction. The tensile performance of such frames was also simulated using ANSYS-based models and was experimentally verified. A correlation with the results of the FEM simulations of mechanical properties was established. The maximum tensile strength of 415 MPa was found for sample 1: G-E (glass–epoxy composite) and the minimum strength of 146 MPa was found for sample 2: F-G-E (G-4) (flax–glass–epoxy composite). The trends were similar, as obtained by simulation using ANSYS. A comparison of the results showed the accuracy of the numerical simulation and experimental specimens with a maximum error of about 8.05%. The experimental study of the tensile properties of polymer matrix composites was supplemented with interlaminar shear strength, and a high accuracy was found. Further, the maximum interlaminar shear strength (ILSS) of 18.5 MPa was observed for sample 1: G-E and the minimum ILSS of 17.0 MPa was observed for sample 2: F-G-E (G-4). The internal fractures were analyzed using a computer tomography analyzer (CTAn). Sample 2: F-G-E (G-4) showed significant interlaminar cracking, while sample 1: G-E showed fiber failure through the cross section rather than interlaminar failure. The results indicate a practical solution of a polymer composite frame as a replacement for existing heavier components in a car, thus helping towards weight reduction and fuel efficiency. Full article

The emerging thermoplastic composite material PEKK exhibits superior thermal stability compared to PEEK. In this work, CF/PEKK laminates were fabricated using laser-assisted heating in AFP, and the effects of repass treatment on the mechanical properties and microstructure of the laminates were compared. The results show that after a single repass treatment, the tensile strength of the laminates increased by 28.39%, while the interlaminar shear strength increased by 11.9%, likely due to the distinct load-bearing components under the two loading conditions. Additionally, the repass treatment significantly improves the fiber/resin interface and surface roughness of the laminates. Full article

The poor interlaminar fracture toughness is a critical limiting factor for the structural applications of aramid fiber/epoxy resin composites. This study investigates the effects of laser-induced graphene (LIG) and short Kevlar fibers on the interfacial toughness and damage detection of aramid composite materials. Mode II tests and tensile tests were conducted to evaluate mechanical properties and damage detection using the piezoresistive characteristics of LIG. The results indicate that LIG combined with short Kevlar fibers significantly enhances the interfacial toughness of the composites, achieving a 381.60% increase in initial Mode II fracture toughness. Although LIG reduced the tensile strength by 14.02%, the addition of short Kevlar fibers mitigated this effect, preserving the overall mechanical performance. Scanning electron microscopy (SEM) analysis revealed enhanced toughening mechanisms, including increased surface roughness, altered crack propagation paths, and fiber bridging. Additionally, LIG enabled real-time damage monitoring, showing a significant increase in resistance upon delamination or crack propagation and a marked increase in resistance upon the tensile fracture. This research indicates that the synergistic effects of LIG and short Kevlar fibers not only enhance the interlaminar toughness of aramid composites but also provide a novel strategy for effective damage detection in fiber-reinforced materials. Full article

In large format additive manufacturing (LFAM), a keener understanding of the relationship between the manufacture method and material temperature dependency is needed for the production of large polymer parts. Statistical analyses supported by material properties and a meso-structural understanding of LFAM are applied to elucidate tensile data trends. The data from LFAM polyethylene terephthalate glycol with 30% carbon fiber (CF) (PETG CF30%) panels (diagonal, horizontal, and vertical in the x-y print plane) and injection-molded specimens tensile tested at six different testing temperatures (room temperature, 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C) were used for statistical analyses. A standard deviation, a coefficient of variation, and a two-way and one-way analyses of variance (ANOVA) were conducted. The manufacturing method (44.2%) and temperature (47.4%) have a strong effect on the ultimate tensile strength, in which temperature (82.6%) dominates Young's modulus. To explain the difference between the ultimate tensile strength of vertical, diagonal, and horizontal specimens at room temperature, a visual inspection of the specimen failure was conducted and the maximum stress at the crack tip was calculated analytically. The decreased strength in the diagonal specimens resulted from the reliance on interlaminar adhesion strength. Future work will consider the effect of the void space variation on tensile strength variance. Full article

This review is a fundamental tool for researchers and engineers involved in the design and optimization of fiber-reinforced composite materials. The aim is to provide a comprehensive analysis of the mechanical performance of composites with epoxy matrices reinforced with carbon nanofibers (CNFs). The review includes studies investigating the static mechanical response through three-point bending (3PB) tests, tensile tests, and viscoelastic behavior tests. In addition, the properties of the composites’ resistance to interlaminar shear strength (ILSS), mode I and mode II interlaminar fracture toughness (ILFT), and low-velocity impact (LVI) are analyzed. The incorporation of small amounts of CNFs, mostly between 0.25 and 1% by weight was shown to have a notable impact on the static and viscoelastic properties of the composites, leading to greater resistance to time-dependent deformation and better resistance to creep. ILSS and ILFT modes I and II of fiber-reinforced composites are critical parameters in assessing structural integrity through interfacial bonding and were positively affected by the introduction of CNFs. The response of composites to LVI demonstrates the potential of CNFs to increase impact strength by reducing the energy absorbed and the size of the damage introduced. Epoxy matrices reinforced with CNFs showed an average increase in stiffness of 15% and 20% for bending and tensile, respectively. The laminates, on the other hand, showed an increase in bending stiffness of 20% and 15% for tensile and modulus, respectively. In the case of ILSS and ILFT modes I and II, the addition of CNFs promoted average increases in the order of 50%, 100%, and 50%, respectively. Full article

This study explores the enhancement of Carbon Fibre Reinforced Polymers (CFRPs) for automotive applications through the integration of modified carbon fibres (CF) and epoxy matrices. The research emphasizes the use of block copolymers (BCPs) and electropolymerisation techniques to improve mechanical properties and interfacial adhesion. Incorporating 2.5 wt.% D51N BCPs in the epoxy matrix led to a 64% increase in tensile strength and a 51.4% improvement in interlaminar fracture toughness. The electropolymerisation of CFs further enhanced interlaminar shear strength by 23.2%, reflecting a substantial enhancement in fibre–matrix interaction. A novel out-of-autoclave manufacturing process for an energy absorber prototype was developed, achieving significant reductions in production time and cost while maintaining performance. Compression tests demonstrated that the modified materials attained an energy absorption rate of 93.3 J/mm, comparable to traditional materials. These results suggest that the advanced materials and manufacturing processes presented in this study are promising for the development of lightweight, high-strength automotive components, meeting rigorous performance and safety standards. This research highlights the potential of these innovations to contribute significantly to the advancement of materials used in the automotive industry. Full article

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. Full article

Continuous carbon fiber-reinforced (CCFR) thermoset composites have received significant attention due to their excellent mechanical and thermal properties. The implementation of 3D printing introduces cost-effectiveness and design flexibility into their manufacturing processes. The light-assisted 3D printing process shows promise for manufacturing CCFR composites using low-viscosity thermoset resin, which would otherwise be unprintable. Because of the lack of shape-retaining capability, 3D printing of various shapes is challenging with low-viscosity thermoset resin. This study demonstrated an overshoot-associated algorithm for 3D printing various shapes using low-viscosity thermoset resin and continuous carbon fiber. Additionally, 3D-printed unidirectional composites were mechanically characterized. The printed specimen exhibited tensile strength of 390 ± 22 MPa and an interlaminar strength of 38 ± 1.7 MPa, with a fiber volume fraction of 15.7 ± 0.43%. Void analysis revealed that the printed specimen contained 5.5% overall voids. Moreover, the analysis showed the presence of numerous irregular cylindrical-shaped intra-tow voids, which governed the tensile properties. However, the inter-tow voids were small and spherical-shaped, governing the interlaminar shear strength. Therefore, the printed specimens showed exceptional interlaminar shear strength, and the tensile strength had the potential to increase further by improving the impregnation of polymer resin within the fiber. Full article