Applied Composite Materials最新文献

This study presents a comprehensive experimental investigation into the performance of lug structures made from Carbon Fibre Reinforced Polymers (CFRP) with three distinct lay-up configurations: Hard (L-C-H), Quasi-Isotropic (L-C-QI), and Soft (L-C-S). The behaviour of these CFRP lugs was compared against conventional metallic aluminium lugs (L-Al) to evaluate their load-bearing performance under uniaxial tensile loading. Among the CFRP configurations, the L-C-QI lay-up exhibited the highest load-bearing capacity, even surpassing that of L-Al. In contrast, the L-C-H lay-up demonstrated the lowest strength within the CFRP group. L-C-S exhibited matrix cracking near the bore hole, facilitating stress relief similar to ductile metals. The L-Al lugs underwent significant plastic deformation and ligament necking, leading to 136% higher energy absorption compared to the best-performing CFRP lug (L-C-QI). Additionally, the study found that as the Hooke’s stiffness of the lugs decreases, the angle between the failure surface and the loading direction increases, indicating a transition in failure mode from shear tear-out to net section tension. Significant delamination was observed on the bearing side of the lug bore hole in CFRP lugs, while aluminium lugs exhibited plasticity on the bearing surface and ligament necking. These findings offer insights into the static tensile behaviour and failure mechanisms of composite and metallic lug structures.

This study investigates the effects of alkali treatment, moisture exposure, and thermal cycling on the mechanical properties of woven jute fiber/epoxy composites. The samples were fabricated with a vacuum-assisted resin infusion technique with untreated and alkali-treated (5% NaOH solution – 4 h) jute fibers. Three levels of thermal cycling profile (-5 ℃ – 65 ℃) as low (50 cycles), medium (250 cycles), and high (500 cycles) were applied to samples that were designated as dry and moisture-exposed (120 h water-soaked samples). Tensile, impact, and hardness tests were conducted to understand the mechanical performance of the samples. Experimental results indicate that alkali treatment improves tensile strength by 17.68%, tensile modulus by 6.01%, and elongation at break by 2.85%, primarily due to enhanced fiber-matrix interaction. Impact strength also increased by 16.54% following alkali treatment. However, exposure to moisture and thermal cycling resulted in significant degradation. Moisture-exposed samples showed reductions of 55.54% in tensile strength, 55.58% in impact strength, and 41.46% in hardness, highlighting the detrimental effects of water absorption. Thermal cycling alone caused tensile strength reductions of 29.50% after 500 cycles due to thermal stresses and micro-crack formation. The results indicate that environmental conditions must be considered for jute/epoxy composites, particularly in humid and temperature-variant mediums. In long-term use, the products may be exposed to more severe conditions and thus the design assumptions could mismatch the practical occurrences.

Needle-punched carbon/carbon composites (NP C/Cs) are extensively utilized in aerospace applications due to their superior mechanical performance at elevated temperatures. However, it is susceptible to oxidation in high-temperature, oxygen-rich environments, leading to alterations in the structure and volume content at the material interfaces, which ultimately compromises their mechanical properties. In this study, the shape evolution curve of circular arc fiber during steady state ablation is derived. Utilizing embedded element technology, an embedded solid beam mixed element model was developed to predict the axial compression behavior of NP C/Cs both before and after oxidation. This approach not only simplifies the model but also enhances computational efficiency. The findings indicate that as the mass loss ratio increases from 0% to 16.84%, the predicted residual elastic modulus ratio decreases from 100.00% to 58.34%, while the residual compressive strength ratio drops from 100.00% to 59.82%. The strong correlation between experimental and simulation results for residual modulus and strength ratios validates the proposed model, confirming its effectiveness in predicting the mechanical performance of NP C/Cs under oxidative conditions.

This study investigates the damage and energy absorption of 3D woven Kevlar/epoxy composites under dynamic impact conditions to clarify their impact resistance. Low velocity impact tests were conducted using a drop weight tester at various velocities. Load-displacement curves and energy absorption results, combined with damage morphology analysis, were used to identify different damage modes and the critical energy for complete penetration. High-speed imaging combined with digital image correlation (DIC) technique was employed to examine the full-field strain distribution and damage evolution during the impact process. An enhanced damage-tracking algorithm was implemented, specifically designed for large out-of-plane deformations and discontinuities and could be broadly applicable to other material systems that undergo large out-of-plane deformations. Results showed that maximum load increased with impact velocity, while bending stiffness remained constant. At lower velocities (1 m/s), elastic behavior with significant rebound was observed, with no delamination or penetration. At 2 m/s, the penetration energy threshold was determined to be 44.3 J, while at 3 m/s, the composite was fully penetrated, showing increased maximum load, displacement, and plastic energy absorption. Higher impact velocities led to longer cracks, with weft cracks consistently exceeding warp cracks in length due to the straight arrangement of weft yarns, which facilitates damage propagation. Microstructural analysis identified fiber fracture, interfacial debonding, and matrix cracking as the main failure modes of the 3D woven Kevlar/epoxy composite. These findings provide valuable insights into the damage mechanisms, strain evolution, and mechanical behavior of 3D woven composites.

A microscopic mechanical model is developed to investigate the mechanical properties and damage behavior of aluminum matrix composites. The effect of particle size distribution and shapes on the properties of aluminum matrix composites is investigated by building three-dimensional (3D) representative volume elements (RVE). The particle size-dependent strengthening and mismatch of thermal expansion strengthening are considered using Taylor-based nonlocal theory of plastic. The damage of matrix is predicted based on the Gurson–Tvergaard–Needleman (GTN) theory. Shear effects are introduced to the GTN model to better describe the failure behavior at low levels of stress triaxiality. A maximum principal stress criterion is used to describe the failure behavior of SiC particles and cohesive behavior is adopted to simulate interface debonding between matrix and particles. Results show that particle size and shape have a significant effect on the failure behaviour of aluminum matrix composites.

This paper presents a numerical methodology developed for the modelling of fatigue life of PA6 long fibre thermoplastic (LFT) material with 40% glass fibre content (PA6-LFT40) produced using compression moulding for the incorporation of long fibre, which enhances the mechanical properties compared to injection-moulding. Firstly, compression moulding process simulations were performed to predict fibre orientation using Autodesk Moldflow. Model parameters for process simulation were calibrated until the predicted fibre orientation matched the orientations obtained using micro X ray-Computer Tomography on PA6-LFT40 plates. The calibrated fibre orientations were then mapped to a finite element method (FEM) solver mesh to perform standard static three point bending test. Tensile tests served as the corresponding material model inputs for the simulations. Using mapped FEM simulation, the deviation between simulation and tests were less than 10% that is much better than without mapping. Finally, using the experimentally determined Haigh diagram, three point bending fatigue testing of PA6-LFT40 at different load levels at a stress ratio of R = -1 were performed and evaluated by using FEMFAT. The predicted fatigue life at different load level showed good correlation with test results. In conclusion, the developed numerical methodology, enhances the predictive modelling of fatigue life of compression moulded LFT Composites.

This study investigates the impact of basalt fiber recovery on the mechanical properties of basalt fiber-reinforced composite laminates via a thermal recycling process in air at 500 °C. Laminates were produced using a hand lay-up technique with six layers of bidirectionally woven basalt fibers and polyester resin. Thermal analyses (DSC and TGA) established that 500 °C is the optimal temperature for complete combustion of the polyester matrix, which is fully removed with minimal impact on the fiber surface. The energy released during resin combustion, measured using the Mahler-bomb method, was evaluated for potential reuse to improve energy efficiency in the recycling process. The basalt fibers exhibited exceptional thermal stability, showing only a 1.75% mass loss during the process. Recovered fibers retained their original continuous woven structure, enabling the fabrication of new laminates. Chemical and morphological assessments of the recycled basalt fibers via Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) confirmed minimal alterations in fiber properties. Mechanical testing using three-point bending revealed that the recycled laminates experienced a decrease in flexural strength and flexural modulus of approximately 10.39% and 4.51%, respectively, compared to virgin laminates. Furthermore, the failure mechanisms differed between the two systems: while virgin laminates failed through a combination of fiber breakage, matrix cracking, and interlayer delamination, the recycled laminates predominantly exhibited interfacial failure. As a result, these findings support the feasibility of recycling basalt fibers with minimal impact on mechanical performance, presenting a sustainable approach for composite material reuse.

This study investigates the viscoelastic behaviour of fibre-reinforced composite sandwich structures (FRPSSs) for marine applications, with an emphasis on the impact of seawater exposure on their damping properties. FRPSSs composed of E glass-fibre/epoxy facesheets and various PVC foam core configurations were evaluated using tensile and dynamic mechanical analysis tests. Moisture uptake during seawater exposure was tracked using gravimetric methods. All samples followed Fickian moisture absorption patterns, which led to reductions in load-bearing capacity, with tensile strength and elastic modulus declining by 35.4% and 8.4%, respectively. Type B specimens showed a 38% greater reduction in storage modulus compared to Type A, while Tan δ increased by 10% for Type A and 5.7% for Type B, indicating higher strain energy dissipation. Type A specimens exhibited superior stiffness and energy dissipation post-exposure. The higher Tan δ indicated greater strain-energy dissipation and a transition toward more viscous behaviour, implying accelerated degradation over time. Prony-series parameters were extracted to support the development of numerical viscoelastic models for optimizing FRPSS designs, enhancing their resistance to out-of-plane damage in marine environments.

The mechanical and fracture behaviors of A359/SiC composites are profoundly influenced by their complex microstructural characteristics, which are not fully understood. Existing micromechanical models often oversimplify particle geometry, neglecting nonconvex shapes, and fail to comprehensively capture the interplay between particle aspect ratio, particle volume fraction, stress distribution, and damage mechanisms. In this study, a novel microstructure-based micromechanical finite element modeling method that incorporates nonconvex particle shapes is proposed to accurately represents the realistic geometry of SiC particles. This approach enables the analysis of how particle characteristics, such as aspect ratio and volume fraction, influence the stress distribution, damage initiation, and fracture propagation in A359/SiC composites. The model accounts for all potential fracture modes, including brittle cracking of SiC particles, ductile damage of the aluminum matrix, and particle–matrix interface debonding. Results demonstrate that the tensile strength and elongation both increase as the particle aspect ratio rises. Needle-shaped particles exhibit superior load bearing capacity and serve as more effective reinforcements compared to stubby-shaped particles. Although increasing the particle volume fraction enhances the fracture strength of the composite, the elongation is reduced concurrently due to the brittleness of the particles and the intensified stress concentration. This study provides a significant advancement over previous models by incorporating realistic particle geometries and offering new insights into the role of microstructure in governing the mechanical and fracture behaviors of A359/SiC composites. The findings are critical for property optimization and material design of A359/SiC composites.

The composite bolted T-joint, consisting of internal laminate skeleton and external skin, presents substantial potential for replacing aluminum alloys as the primary load-carrying connection structure. However, its complex failure mechanisms and numerous design parameters pose challenges for engineering applications. To identify critical design parameters significantly impacting its bending performances, a validated finite element model of this T-joint under bending loads was established. Using uniform design and multiple linear regression methods, the significance of 15 design parameters related to machining, configuration, and resin properties on bending performances was systematically investigated and the effect mechanisms of certain parameters were discussed. The results show that parameters such as the base panel bolt hole radius (r_B), corner radius (r_C), the thickness of the upper surface skin (t_U), base panel skeleton (t_{S_B}), and lug skeleton (t_{S_L}) have significant positive effects. Failure of the resin area between the skin and skeleton results in localized weak stress area in the skin, thereby reducing the overall load-carrying capacity of the joint. r_B has an optimal value that balances bending performances and fastener weight. The final failure location of the joint is either in the base panel skeleton or lug skeleton, depending on the relative thickness of each. Additionally, when designing composite T-joints with multiple configuration components for primary load-carrying connections, it is advisable to place weak load-carrying positions away from the load-carrying core.