Carbon Fiber-reinforced Composites Research Articles

Enhanced interlayer strength in 3D-printed PA12 composites via electromagnetic induction post-processing

Weak interlayer strength remains a critical limitation in the application of material extrusion 3D-printed parts. Herein, a non-contact method, electromagnetic induction post-processing, is proposed to address this issue. This method aims to enhance the weak interlayer strength of 3D-printed PA12 samples by introducing Fe3O4 particles for induced heat generation under alternating magnetic fields. The heat generation characteristics, surface morphology, crystallization behavior, and interlayer performance of 3D-printed samples subjected to induction post-processing are systematically investigated. The results indicate that a remarkable improvement in the interlayer strength of 3D-printed PA12 samples can be achieved through induction post-processing. Tensile strength along the Z-direction (perpendicular to the printing plane) exhibits a distinct increase of 218.3 %, while interlayer tear strength can rise by 328.1 %. Improvement in interlayer strength results from heat generation driving interfacial resin diffusion. Additionally, induction post-processing results in localized surface smoothing and a slight reduction in the crystallinity of the 3D-printed sample. Compared to traditional methods like in-oven heat treatment (annealing), induction post-processing offers higher efficiency by circumventing the initial constraints of heat transfer. Furthermore, the concept of selective induction heating (SIH) is proposed to achieve non-contact, localized heating by adjusting the composition of thermoplastics during printing. SIH holds good promise for applications in 3D-printed continuous carbon fiber-reinforced thermoplastic composites, including mold-free forming, complex surface welding, and repair (particularly in narrow and inaccessible areas).

Mechanical Characterization and Production of Various Shapes Using Continuous Carbon Fiber-Reinforced Thermoset Resin-Based 3D Printing.

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.

An anchor-inspired interface for improving interfacial properties of carbon fiber-reinforced high-performance thermoplastic composites

Carbon fiber-reinforced thermoplastic composites are promising materials with many application prospects. However, surface inertness of CFs weakens the interfacial properties of these composites. Therefore, in this study, an anchor-inspired structure was designed and grafted onto CFs by using an anchor-inspired segmented copolymer, comprising of polyimide as the “chain” and polyhedral oligomeric silsesquioxane (POSS) as the “anchor”. In combination with atom transfer radical polymerization with the advantage of controllable molecular weight, degree of polymerization of the anchor-shaped structure with the best compatibility with poly (phthalazinone ether nitrile ketone) (PPENK) resin was pre-determined through molecular dynamics simulations, which reduced the experimental costs. The results of X-ray photoelectron spectroscopy indicated the successful connection of the numerous anchor-shaped structures to the CFs. Compared to composite made of origin fibers and PPENK, the interfacial shear strength at the microscopic level and interlaminar shear strength at the macroscopic level of grafted CF and PPENK composite increased by 184.9 % and 44.2 %, respectively. This is mainly attributed to the synergistic effect of mechanical interlocking and interfacial interaction between the anchor-shaped structure and the PPENK resin. This study serves as a feasible path to enhance the interfacial adhesion of composites by designing an anchor-shaped structure of organic macromolecules and inorganic nanoparticles on CFs.

Process design and experimental study on drilling operations of a hybrid aluminum/carbon fiber reinforced polymer/titanium composite

ABSTRACT Carbon fiber reinforced composites (CFRP) are increasingly used in aviation and automotive industries. To enhance rigidity and fatigue resistance, aluminum (Al) and titanium (Ti) alloys are used together with CFRP materials. Drilling is a common method for manufacturing these hybrid composite stacks. This study examines the impact of process parameters, temperature, tool wear, thrust force, and torque on CFRP/Al/Ti hybrid composites during dry machining. Tests were conducted at various drilling speeds, feed rates, and stack orders using a solid carbide (WC) cutting tool. Results indicate that feed rate has a significant effect on the process outputs. The temperature remains low as the feed rate rises. The delamination factor is the highest in the Ti\\CFRP\\Al stack. In addition, delamination and temperature rise with increasing cutting speed. Finally, while the Al\\CFRP\\Ti stacking order performs poorly in terms of tool wear, it is measured more than 330 micrometers at the lowest feed rate.

Copper metallization of carbon fiber-reinforced epoxy polymer composites by surface activation and electrodeposition

The application of polymer metallization in lightweight and high-strength materials for the sporting goods, automotive, aerospace and construction sectors has attracted considerable attention. The present study aims to deposit a thin, uniform copper (Cu) layer on an epoxy‑carbon fiber (epoxy-Cf) composite material for lightweight, high-frequency radio reflector applications (Ka-Band and higher frequencies) required in space missions. In this work, a surface-activated electroplating technique in which the surface of the substrate is activated with a Sn/Ag system, followed by conventional electroplating is studied. Surface activation deposits layers of conducting metal ions on the surface of the epoxy-Cf composite, which significantly improves the electrical conductivity of the composite surface. The subsequent electrodeposition takes place from a CuSO4 solution with a pH value of 4 at three different current density values of 0.05 A/dm2, 0.5 A/dm2 and 1 A/dm2. The presence and abundance of metallic Cu over epoxy-Cf composite were confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The morphology and elemental composition of the coating were characterized by scanning electron microscopy equipped with energy dispersive spectroscopy. With current density and coating thickness, morphology of the deposit changed from cauliflower-like to spherical along with grain refinement. Microhardness test shows a hardness of 330 HV and the pull-off adhesion test gave a bond strength of 1.69 MPa for 27.56 μm thick copper deposit. A major challenge encountered during the deposition of Cu is the oxidation of the metal followed by immediate tarnishing. This issue has been effectively addressed by employing benzotriazole solution as a protective agent.

Ultrarapid soldering Cf/Al by inactive solder by ultrasonic assistance

Ultrasonic vibration was applied when soldering carbon fiber-reinforced aluminum composites (Cf/Al) in this work. The effects of ultrasonic action time on joint formation, carbon fiber distribution, and mechanical properties of the joints were studied. Results show that, with the assistance of ultrasonic vibration, inactive solder can wet the carbon fiber within dozens of seconds at low temperature (250 °C). Short ultrasonic action time leads to minor erosion of aluminum substrate, thereby restricting the movement of carbon fibers into joint. Extensive erosion of the aluminum occurs with prolonged ultrasonic action time. A uniform distribution of carbon fibers in joint is achieved at 60 s. Wetting of carbon fiber is characterized by amorphous-nanocrystalline oxides on its surface, which can be attributed to the elevated temperature and pressure induced by the cavitation of the solder. Extending ultrasonic time enhances the hardness and the shear strength of the joint. The failure cracks propagate through the substrate when ultrasonic time exceeds 15 s. This work provides referential value when soldering materials with low surface energies.

Comparing Degradation Mechanisms, Quality, and Energy Usage for Pellet- and Filament-Based Material Extrusion for Short Carbon Fiber-Reinforced Composites with Recycled Polymer Matrices

Short carbon fiber (sCF)-based polymer composite parts enable one to increase in the material property range for additive manufacturing (AM) applications. However, room for technical and material improvement is still possible, bearing in mind that the commonly used fused filament fabrication (FFF) technique is prone to an extra filament-making step. Here, we compare FFF with direct pellet additive manufacturing (DPAM) for sCF-based composites, taking into account degradation reactions, print quality, and energy usage. On top of that, the matrix is based on industrial waste polymers (recycled polycarbonate blended with acrylonitrile butadiene styrene polymer and recycled propylene), additives are explored, and the printing settings are optimized, benefiting from molecular, rheological, thermal, morphological, and material property analyses. Despite this, DPAM resulted in a rougher surface finish compared to FFF and can be seen as a faster printing technique that reduces energy consumption and molecular degradation. The findings help formulate guidelines for the successful DPAM and FFF of sCF-based composite materials in view of better market appreciation.

Clinching of Carbon Fiber-Reinforced Composite and Aluminum Alloy

The extensive use of carbon fiber-reinforced composites and aluminum alloys represents the highest level of automotive body-in-white lightweighting. The effective and secure joining of these heterogeneous materials remains a prominent and actively researched topic within the scientific community. Among various joining techniques, clinching has emerged as a particularly cost-effective solution, experiencing significant advancements. However, the application of clinching is severely limited by the properties of the joining materials. In this work, various clinching processes for the joining of composites and aluminum alloys reported in recent research are described in detail according to three broad categories based on the principle of technological improvement. By scrutinizing current clinching technologies, a forward-looking perspective is presented for the future evolution of clinching technology in terms of composite–aluminum joints, encompassing aspects of tool design, process analysis, and the enhancement of joint quality. This work provides an overview of current research on clinching of CFRP and aluminum and serves as a reference for the further development of clinching processes.

Phase stability of W-containing high-entropy carbide with silicon addition at high temperatures

Reactive melt infiltration (RMI) is a typical method to produce carbon fiber-reinforced ultra-high temperature ceramic matrix composites (Cf/UHTCs), for which the molten Si is a very general and practical infiltrator. High-entropy carbide (HE-carbide) is a newly developed promising matrix phase of Cf/UHTCs. Understanding the phase equilibrium relation in the HE-carbide and Si reaction system can provide accurate guidance on designing the RMI process for preparing HE-carbide matrix composites with controlled phases and microstructure. This study systematically investigates W-containing HE-carbide and Si addition reactions at high temperatures. Samples with nominal starting compositions of (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C-xSi (HEC-xSi, x = 2.5, 5 and 10 wt%) are prepared by spark plasma sintering technique at 1500 °C and 1700 °C with an axial pressure of 40 MPa for 10 min. The results show that adding 2.5 wt% or 5 wt% Si removes carbon from the HEC matrix, forming SiC and stable equimolar (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C1-x phase with carbon deficiency at high temperatures. In contrast, besides the SiC phase, the addition of 10 wt% Si in the HEC matrix may form unstable transient phases of (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C1-x with supersaturated carbon deficiencies at high temperatures, which finally decomposes into non-equimolar HE-carbide (Ti0.2Zr0.2Hf0.2Ta0.2W0.2-y)C1-z and metal silicide WSi2 phases. The effects of the HEC and Si reactions on the microstructure evolution of the samples during sintering are discussed. Meanwhile, the mechanical properties of the samples with the reaction resulting microstructure are measured and briefly discussed.

Comparison of Mechanical Property Simulations with Results of Limited Flexural Tests of Different Multi-Layer Carbon Fiber-Reinforced Polymer Composites.

This article is focused on the experimental study of flexural properties in different multi-layer carbon fiber-reinforced polymer (CFRP) composites and correlations with the results of finite element method (FEM) simulations of mechanical properties. The comparison of the results shows the possibility of reducing the number of experimental specimens for testing. The experimental study of flexural properties for four types of carbon fiber-reinforced polymer matrix composites with twill weaves (2 × 2) was carried out. As input materials, pre-impregnated carbon laminate GG 204 T and GG 630 T (prepreg) and two types of carbon fiber fabrics (GG 285 T and GG 300 T (fabric)) were used. Multi-layer samples were manufactured from two types of prepregs and two types of fabrics, which were hand-impregnated during sample preparation. The layers were stacked using same orientation. All specimens for flexural test were cut with the longer side in the weft direction. Pre-impregnated carbon laminates were further impregnated with resin DT 121H. Carbon fabrics were hand-impregnated with epoxy matrix LG 120 and hardener HG 700. To fulfill the aim of this research, finite element method (FEM)-based simulations of mechanical properties were performed. The FEM simulations and analysis were conducted in Hexagon's MSC Marc Mentat 2022.3 and Digimat 2022.4 software. This paper presents the results of actual experimental bending tests and the results of simulations of bending tests for different composite materials (mentioned previously). We created material models for simulations based on two methods-MF (Mean Field) and FE (Finite Element), and the comparative results show better agreement with the MF model. The composites (GG 285 T and GG 300 T) showed better flexural results than composites made from pre-impregnated carbon laminates (GG 204 T and GG 630 T). The difference in results for the hand-impregnated laminates was about 15% higher than for prepregs, but this is still within an acceptable tolerance as per the reported literature. The highest percentage difference of 14.25% between the simulation and the real experiment was found for the software tool Digimat FE 2022.4-GG 630 T composite. The lowest difference of 0.5% was found for the software tool Digimat MF 2022.4-GG 204 T composite. By comparing the results of the software tools with the results of the experimental measurements, it was found that the Digimat MF 2022.4 tool is closer to the results of the experimental measurements than the Digimat FE 2022.4 tool.

Quasi-static uniaxial compression and low-velocity impact properties of composite auxetic CorTube structure

Auxetic structures are gaining great attention due to their unique contraction deformation characteristics under compression and impact. In this paper, high performance carbon fiber-reinforced composites are used to fabricate the auxetic structure consist of corrugated sheets and tubes (CorTube). The quasi-static uniaxial compression and low-velocity impact properties of composite CorTube structure are explored. The response of the composite CorTube structures under quasi-static compression loads are analyze through a combination of theoretical analysis, simulations, and experimental tests. Additionally, drop-weight impact tests are conducted using a rigid impactor with a hemispherical head to examine the effects of impact energy levels, impact locations, and corrugated sheet thickness on the impact response of CorTube structure. Enhancing corrugated sheet-tube bonding via modified cross members and reducing tube crushing during quasi-static compression are notable findings. The results also highlight the remarkable auxetic properties of the composite CorTube under low-speed impact, and the impact resistance could be enhanced by increasing the corrugated sheet thickness and stiffness. Various failure modes were observed, including cracks, pits, tube crushing, and delamination. Significantly, peak-impacted specimens exhibited greater maximum displacement with lower peak impact forces. This study offers insights into the deformation and failure modes of auxetic CorTube structures under low-velocity impact.

Electronic effects of substituents on the properties of recyclable epoxy resins containing aromatic acetal groups

Both environmental and economic concerns are pioneering the development of recyclable thermosetting polymers. In this study, three liquid acetal-containing di-epoxide monomers (ADEs) with different para-substituted (-OCH3, -Cl and –NO2) phenyl groups were synthesized. The refractive indices and viscosities of the three di-epoxide liquids increase in the sequence of ADE-3 (-OCH3), ADE-1 (-Cl) and ADE-2 (-NO2). Once cured with methylhexahydrophthalic anhydride, the three cured ADEs exhibit high glass transition temperatures (181–218 °C). Due to the presence of dynamic acetal bonds, all three cured ADEs are reprocessable, repairable, weldable, and degradable. Interestingly, the electronic effect of the substituents on the phenyl group significantly impacts the structural configuration, reprocessability and degradation behaviors of the resultant cured ADEs. As the electron-withdrawing effect of the substituents on the phenyl group increases, the stress relaxation rates of the cured ADEs decrease at the same temperature. Under optimized reprocessing conditions, the reprocessed ADE-1 (-Cl) and ADE-2 (-NO2) resins show the highest (117 %) and lowest (67 %) retention rates for tensile strength, respectively. The degradation rates of the three cured ADEs in the acidic solutions decrease with increasing the electron-withdrawing effect of the substituent on the phenyl group. Finally, a di-epoxide curing system based on ADE-3 was applied to prepare carbon fiber-reinforced composites, and nondestructive recovery of the carbon fibers was attained by degradation of the resin matrix.

Additive manufacture of programmable multi-matrix continuous carbon fiber reinforced gradient composites

Bio-inspired gradient materials and structures, including cartilage scaffolds, soft actuators, and sensors, demonstrate significant potential applications in the fields of biomedicine, robotics, and flexible electronics. This paper introduces a novel method for fabricating continuous fiber-reinforced gradient composites using additive manufacturing techniques. In-situ impregnation 3D printing of two distinct matrix materials and continuous fibers was realized utilizing a specially designed multi-channel nozzle. This allowed for the personalized distribution of matrix materials within the composite by controlling the extrusion rates. Employing polylactic acid (PLA) and thermoplastic polyurethane (TPU), which possess differing mechanical properties, as matrix materials, the study examined the tensile and three-point bending mechanical properties of continuous carbon fiber-reinforced PLA/TPU (CCFR-PLA/TPU) composites with varying ratios of the two matrix materials. Moreover, the ability to control the distribution of matrix materials enabled the tailoring of gradient composites. Additionally, this research investigated the fabrication and compression behavior of gradient thin-walled structures and lattice structures composed of CCFR-PLA/TPU composites. The findings suggest that this programmable, multi-material, continuous carbon fiber-reinforced composites additive manufacturing approach can fabricate composites with a broad spectrum of tunable mechanical properties.

Simulation of tensile fatigue crack propagation in carbon fiber unidirectional laminates under progressive fatigue damage model

Abstract This paper predicts and analyzes the tensile fatigue crack propagation of carbon fiber reinforced unidirectional laminates at high-stress levels using the carbon fiber stiffness strength degradation formula. The results show that different paving modes significantly affect crack propagation and stress distribution. Under the 45° layup, two cracks appeared. The upper crack expanded along the fiber direction, and the lower crack first appeared as a horizontal crack at the constrained end and then along the fiber direction. Under 0° layering, vertical cracks appear at the prefabricated crack tip, and the crack direction is the same as the loading direction. At a -45° layup, two cracks appeared at the prefabricated crack tip, and then the lower crack extended to the integral separation of the test piece. In addition, the strain characteristic analysis shows that the strain increases and decreases rapidly during crack propagation. This study has a certain reference value for further understanding of fatigue crack propagation characteristics of carbon fiber-reinforced composites.

PAN-precursor to carbon fibre: An investigation of manufacture and material properties for varying comonomer composition

This study presents the conversion of polyacrylonitrile (PAN) co-polymers containing methyl acrylate (MA) and varying concentrations of itaconic acid (IA) comonomers, from precursor fibre into carbon fibre using pilot scale continuous processes. The impact of itaconic acid on fibre processability, thermal behaviour, energy consumption, and final mechanical properties during thermal oxidative stabilization (TOS) and carbonization are investigated. Itaconic acid concentration varies from 0.3 to 3 wt % and with increasing concentration of itaconic acid, the precursor fibre exhibited lower exothermicity and enhanced reactivity, resulting in 7 % less energy consumption during stabilization. Higher itaconic acid content led to improved carbon fibre properties. A 20 % increase in tensile strength was recorded for carbon fibres containing the highest amount of itaconic acid along with a higher amount of graphitic structure and carbon yield. Overall, this study explores the impact of precursor design on fibre properties as a route to the manufacture of carbon fibre with reduced embodied energy. The results of this study illustrate pathways to improve the efficiency and effectiveness of carbon fibre production, and to ultimately create high-performance, lightweight, and more sustainable carbon fibre-reinforced composites.

Experimental and numerical study on moisture diffusion behavior of 3D woven composite

In this paper, a meso-scale finite element model was established to investigate the moisture diffusion in 3D woven carbon fiber reinforced composites (CFRCs), and to analyze the internal stresses caused by hygroscopic deformation. To quickly obtain the mesoscopic moisture diffusion parameters, an optimization procedure that fitted the simulation results to the experimental results was implemented to achieve automatic inverse identification of each parameter. The homogenized analytical models for describing the moisture diffusion in yarns and resin, specifically Fick’s and Langmuir-type models, were evaluated. The results indicated that Langmuir-type model provided more accurate fitting results, attributed to its consideration of anomalous moisture absorption. Furthermore, the internal stress induced by moisture absorption was analyzed for composites aging at 82 °C over different time intervals. The accumulation of hygroscopic stress was observed at the intersection of warp and weft yarns, as well as at the interface between the weft yarn and matrix.

Optimising Recycling Processes for Polyimine-Based Vitrimer Carbon Fibre-Reinforced Composites: A Comparative Study on Reinforcement Recovery and Material Properties.

We investigated the recycling process of carbon fibre-reinforced polyimine vitrimer composites and compared composites made from virgin and recycled fibres. The vitrimer matrix consisted of a two-component polyimine-type vitrimer system, and as reinforcing materials, we used nonwoven felt and unidirectional carbon fibre. Various diethylenetriamine (DETA) and xylene solvent ratios were examined to find the optimal dissolution conditions. The 20:80 DETA-xylene ratio provided efficient dissolution, and the elevated temperature (80 °C) significantly accelerated the process. Scaling up to larger composite structures was demonstrated. Scanning electron microscopy (SEM) confirmed effective matrix removal, with minimal residue on carbon fibre surfaces and good adhesion in recycled composites. The recycled nonwoven composite exhibited a decreased glass transition temperature due to the residual solvents in the matrix, while the UD composite showed a slight increase. Dynamic mechanical analysis on the recycled composite showed an increased storage modulus for nonwoven composites at room temperature and greater resistance to deformation at elevated temperatures for the UD composites. Interlaminar shear tests indicated slightly reduced adhesion strength in the reprocessed composites. Overall, this study demonstrates the feasibility of recycling vitrimer composites, emphasising the need for further optimisation to ensure environmental and economic sustainability while mitigating residual solvent and matrix effects.

Mechanical characterization of 3D-Printed carbon fiber-reinforced polymer composites and pure polymers: Tensile and compressive behavior analysis

AbstractFused deposition modeling (FDM) 3D printing is widely utilized for producing thermoplastic components with functional purposes. However, the inherent mechanical limitations of pure thermoplastic materials necessitate enhancements in their mechanical characteristics when employed in certain applications. One strategy for addressing this challenge involves the incorporation of reinforcement materials, such as carbon fiber (CF), within the thermoplastic matrix. This approach leads to the creation of carbon fiber-reinforced polymer composites (CFRPs) suitable for engineering applications. The utilization of CFRPs in 3D printing amalgamates the benefits of additive manufacturing, including customization, cost-effectiveness, reduced waste, swift prototyping, and accelerated production, with the remarkable specific strength of carbon fiber. This study encompasses tensile and compressive testing of distinct material compositions: recycled polylactic acid (rPLA), PLA enriched with 10 wt.% carbon fiber, pristine polyethylene terephthalate glycol (PETG), and PETG bolstered with 10 wt.% carbon fiber. Tensile tests adhere to the ASTM D3039 standard for specimens of rectangular shape, while the ASTM D695 standard governs the compressive testing procedures. Additionally, an inquiry into the influence of the primary 3D printing build orientation parameter on the tensile and compressive strengths of diverse materials was conducted. The outcomes reveal that rPLA exhibits superior mechanical properties in both tensile and compressive tests, irrespective of flat or on-edge build orientations. In the context of tensile strength analysis, it is noteworthy that rPLA demonstrated a superior performance, surpassing CFPLA by 30% in flat orientation and exhibiting a remarkable 39.2% advantage in on-edge orientation. Moreover, PLA reinforced with carbon fiber exhibits superior tensile and compressive properties compared to its PETG counterpart. A comparative analysis between CFPLA and CF-PETG indicates that CF-PLA demonstrates higher tensile strengths, with increases of 26.6 and 27.6% for flat and on-edge orientations, respectively. In the context of compressive strength analysis, rPLA surpassed CFPLA, PETG, and CF-PETG by 23.7, 53, and 67%, respectively. Intriguingly, the findings indicate that the incorporation of 10 wt.% carbon fiber diminishes the tensile and compressive properties in comparison to pure PETG.

Machine learning-based determination of Mode II translaminar fracture toughness of composite laminates from simple V-notched shear tests

This paper presents a novel method for measuring the translaminar crack resistance curve of composite laminates under Mode II shear loading. A machine learning (ML)-based approach is utilized to extract the inapparent information of the crack resistance curve from the translaminar shear strength measurements obtained from simple V-notched shear tests. The entire campaign is built on the framework of the Finite Fracture Mechanics (FFM) combined with Finite Element Method (FEM). Special emphasis is made on the nonlinear mechanical behavior of composites under shear stress since the original FFM models are designed for quasi-brittle materials. With the well-trained recurrent neural network model, the Mode II R-curve of composite laminate can be obtained with un-notched and V-notched shear strength values as inputs. Experiments were conducted on carbon fiber-reinforced composites to validate the accuracy of the R-curve obtained by the proposed approach and that by the traditional compact shear test. The successful implementation of the method suggests a more convenient and low-cost way of obtaining this important damage-related parameter for composites.

Research on Microwave Pyrolysis Recovery and Reuse Performance of Carbon Fiber Composites.

Carbon fiber-reinforced resin matrix composites find extensive applications across various industries. However, their widespread use also generates significant waste, leading to resource depletion and environmental concerns. Studying the production of composite materials using recovered carbon fiber is imperative to mitigate the environmental impact associated with waste from carbon fiber-reinforced resin matrix composites and optimize resource utilization. In this study, carbon fiber was reclaimed using the microwave pyrolysis-oxidation process. The reclaimed carbon fiber underwent a cutting process to produce shorter carbon fibers tailored to specific requirements, which were then used to fabricate composite plates reinforced with epoxy resin. The mechanical characteristics of the composite were analyzed, along with SEM, XPS, infrared, Raman, and contact angle analyses conducted on the recovered carbon fiber. The test findings suggested minimal variation in the surface morphology of the recovered carbon fiber materials. Post-recovery, an increase in the quantity of oxygen-containing functional groups was observed on the carbon fiber surface. Additionally, the contact angle between the carbon fiber surface and the epoxy adhesive decreased. The mechanical properties of the composite produced from the recovered carbon fiber decreased, including the impact strength, tensile strength, and bending strength, with the impact strength dropping by 24.14%, tensile strength by 15.94%, and bending strength by 8.24%, while maintaining overall reusability, thus paving the way for the comprehensive utilization of carbon fiber resources.