Applied Composite Materials最新文献

The long-term electromagnetic interference shielding performance of hybrid epoxy nanocomposites was investigated after sustained hydrothermal ageing. Epoxy matrices were co-filled with multi-walled carbon nanotubes (MWCNTs, 0.05–1 vol%) and carbon-coated copper nanoparticles (Cu@C, 5 vol%) and then immersed in a 0.1 wt% NaCl solution at 80 °C for 1000 h. Gravimetric analysis revealed a maximum mass uptake of about 1 wt%, followed by partial leaching of low-molar-mass species. Ageing induced a one-order-of-magnitude rise in room-temperature conductivity (up to 0.21 S m⁻¹) and a sixfold increase in effective permittivity (ε′ ≈ 1100 at 0.573 kHz). During a single heating–cooling cycle to 500 K, the electrical conductivity showed almost the exact same behaviour as seen in non-aged composites, indicating low to no effect of hydrothermal ageing on structural relaxation or thermally activated epoxy-filler interactions. Across the 26–37 GHz Ka-band, total shielding effectiveness (SE_T) remained 4–9 dB with absorption (up to 0.67) dominating over reflection. A slight (< 2 dB) enhancement in the low-frequency range of Ka-band was recorded. The combination of a resilient microstructure and stable EMI performance shows that MWCNT/Cu@C/Epoxy hybrids offer durable, hydrothermally stable shielding, which is ideal for humid or saline conditions in marine or aircraft settings, especially for radar-related systems.

Damage caused by low velocity impacts in composite materials may go undetected, resulting in significant damage being unnoticeable. This phenomenon has been studied using experiments and simulations on a typical composite material, Toray T1225 LM-PAEK UD Tape, following impacts with varying energy levels. To the authors’ knowledge, there is a lack of information on thermoplastics and compression after impact (CAI) in the publicly available literature, and there have been insufficient results and discussions regarding CAI tests on thermoplastic composite materials at the relatively high levels of impact used, especially with the rise in the use of thermoplastic materials for the advanced air mobility market. This paper provides experimentally gathered data and describes a numerical approach to aid in the prediction of CAI strength for materials that are of interest to the advanced air mobility market. It has been observed that compressive strength decreases significantly even for a range of damage growth and levels of impact energy. This decrease occurs with damage (dent depth) below 0.1 inches (2.54 mm (mm)) and impact energy well below 30 Joules, even though the resulting damage may be barely visible. Finite element (FE) simulation was carried out to better understand the development and growth of damage in the composite material during the CAI tests. There exist a few restrictions to implement a high-fidelity CAI model. Dynamic instability resulting from the impact must be suppressed during compression by employing mass scaling with a significantly low target time increment. The complexity of problems and need for detail make current models take days to run, even on high performance computing (HPC) clusters. Therefore, a “simplified” CAI test was implemented in ABAQUS using symmetric boundary conditions (BCs), even when the composite had +/-45° plies and lacked full symmetry. This approach allowed testing different quarters of the full CAI specimen to identify which one showed the most damage and lowest compressive strength. The design ultimate load (DUL) has been selected based on the experimental and simulation results, considering a safety factor suitable for the ranges of static loadings when barely visible impact damage (BVID) occurs.

This study focuses on T700 composite bolted single-lap joints, systematically investigating how varying impact energies and locations affect the connection performance of bolted structures. The energy value for altering the failure modes of single-lap joints is explored through experimental methods. A high-precision numerical model is established to analyze the damage mechanism of the failure behavior in CFRP bolted single-lap joints after impact. The results indicate that, when the impact energy exceeds 25 J at location A, the failure load of the test specimen significantly decreases, with a reduction rate exceeding 15.49%. The primary failure mode transitions from bearing failure to a delamination-dominated mixed failure, and the bolt tilting angle during failure will change obviously. Under impact with energy of 25 J, the failure load exhibits significant regional variations in the bolted single-lap joints. In which, the lap zone demonstrates optimal residual performance with only a 2.65% reduction, while the lower plate exhibits the most severe degradation, experiencing a 23.96% decrease. This study can provide critical insights for damage-tolerant design of composite bolted joints in aerospace structural applications.

Fabric forming is widely recognized for its efficiency in producing fiber-reinforced composite preforms, but defect suppression in preforms with double-curvature geometries are limited. This study investigates the effect of the blank holder gap (BHG), defined as the distance between the blank holder and the die, on yarn local buckling by developing a forming testbench with adjustable BHG for experimental analysis. Furthermore, a macroscopic finite element model was established to analyze the influence mechanism. With the BHG decreasing, in-plane friction force exerted on the fabric by the blank holder and die increases, which hinders the passive drawing of the warp yarns by the weft yarns. This elevated friction reduces the in-plane bending deformation of the warp yarns and lowers the likelihood of local buckling. However, the increased friction force also intensifies the slippage between adjacent yarns, enlarging the gaps between them and consequently reduces the fiber volume fraction of the component. These findings offer valuable guidance for optimizing BHG to achieve a balance between yarn local buckling suppression and slippage in the forming of complex composite preforms.

Carbon nanotube (CNT)-reinforced fiber composites show great promise in aerospace and defense due to their lightweight nature, high strength-toughness balance, and broadband microwave absorption. This review systematically examines the mechanical reinforcement and wave-absorption mechanisms in CNT composites. We focus on the key challenge of synergizing mechanical and electromagnetic performance, analyzing recent advances in multiscale modeling and intelligent optimization algorithms. Research shows that CNT dispersion morphology, alignment, and content critically control material properties: randomly dispersed CNTs enhance interlaminar strength through balanced interfacial stress, while axially aligned CNTs improve mechanical load-bearing. Magnetic-CNT heterointerface designs optimize impedance matching and energy dissipation for broadband absorption. Molecular dynamics-finite element coupled models and multi-objective optimization algorithms reveal dynamic links between microstructures and macro-properties, providing a theoretical framework for dual-functional “mechano-electromagnetic” materials. Future work must address bottlenecks in nanoscale characterization accuracy, cross-scale design, and environmental adaptability to advance industrial applications of load-bearing microwave-absorbing composites.

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This study investigates the fabrication and characterization of short carbon fiber-reinforced epoxy composite honeycomb structures with moderate to high strength, featuring triangular (T), hexagonal (H), and square (S) core designs. These structures are produced using direct ink writing (DIW) 3D printing with customized epoxy inks formulated with 10–40 wt% carbon fibers and rheological modifiers to achieve desired shear-thinning and yielding properties for precise printing of complex geometries. This fabrication approach allowed for mold-free fabrication of bioinspired honeycomb structures with variable core geometries and cell sizes, achieving superior surface finish and dimensional accuracy compared to 3D-printed continuous carbon fiber reinforced thermoplastic composites. The mechanical performance of these structures was engineered by altering geometric configurations, material compositions, and infill densities (30–50%). In-plane compressive tests showed stiffness improvements of 59%, 43%, and 47%, and strength gains of 106%, 93%, and 162% in triangular, hexagonal, and square honeycomb cores, respectively, as infill density increased from 30 to 50% for ink with 40 wt% carbon fiber. Specific strength followed similar trends. Comparisons with scaling laws indicated comparable strength for triangular cores, lower strength for square cores, and higher strength for hexagonal cores, surpassing previously reported values. This study demonstrates the potential of DIW combined with engineered inks to fabricate advanced composite honeycomb cores with tailored properties, offering promising applications in lightweight, high-performance structural designs.

This study investigates the damage process and residual compressive strength of three-dimensional four-directional braided carbon fiber composites under simultaneous impact conditions. By designing different braiding angles between the two impact positions, impact point spacings, and impact methods, impact experiments were conducted on specimens with 15° and 30° braiding angles using an impact energy of 30 J, along with ultrasonic C-scan for damage detection. Experimental results show that when the impact point spacing is small, the simultaneous impact effect is significant, leading to a larger damage area and lower residual strength. In contrast, when the impact point spacing is large, the damage area decreases, and the residual strength increases. Different braiding angle significantly influence the damage propagation of the specimens. The specimens with a 15° braided angle exhibit damage primarily along the longitudinal direction, whereas the specimens with a 30° braiding angle show more uniform damage. The impact method has a minimal effect on the remaining strength of the 15° specimens, indicating their superior strength performance, whereas the 30° specimens exhibit a more pronounced nonlinear failure mode. This study provides a theoretical basis for optimizing the performance of composite materials under complex impact environments.

This study investigates the water absorption behavior of 3D-printed amorphous PEEK and short carbon fiber-reinforced PEEK (PEEK-CF) produced via fused deposition modeling. Water uptake was measured in distilled and seawater over extended exposure (~1125 h). PEEK-CF samples in seawater exhibited the highest absorption by mass (~6% increase), while PEEK and PEEK-CF in distilled water reached ~4% increase by mass, and PEEK in seawater reached ~4% increase by mass. The elevated water uptake observed in PEEK-CF compared with unreinforced PEEK is attributed to osmotic pressure and voids at the fiber-matrix interface. Diffusion behavior of the amorphous PEEK and PEEK-CF deviated from Fickian kinetics and followed the Vas-power model (modified Lucas-Washburn equation) more closely. Moisture exposure had a notable impact on mechanical properties: PEEK-CF showed up to a 32% reduction in tensile modulus, whereas the mechanical properties of unreinforced amorphous PEEK remained largely unaffected by water absorption. A modified rule of mixtures incorporating knockdown factors for water uptake, fiber length, and orientation accurately predicted the observed mechanical degradation. These findings underscore the need to consider moisture effects when designing with 3D-printed PEEK-CF composites.

In this study, a combination of numerical simulation and experiment was used to systematically investigate the mechanical response characteristics and damage mechanisms of countersunk hole angles (60°, 90°, 120°) on filled-hole composite laminates and countersunk hole laminates under axial tensile loading. Based on acoustic emission technology to monitor the damage evolution in real time, the damage patterns under static tensile conditions were identified and classified by combining with K-means clustering algorithm. A three-dimensional finite element model was constructed by ABAQUS platform, integrating 3D Hashin failure criterion, B-K damage criterion and zero-thickness cohesive layer method, and the VUMAT subroutine was used to characterize the material failure behavior. The results show that the countersunk hole angle significantly affects the location of delamination damage initiation. Four main damage modes were observed experimentally: fiber/matrix debonding (0–110 kHz), matrix cracking (110–250 kHz), delamination (250–350 kHz) and fiber breakage (350–400 kHz). The tendency for different damage modes to occur in the laminate changes as the countersunk hole angle changes. The comparative analysis of filled hole tension (FHT) and open hole tensile (OHT) of laminates shows that countersunk bolts reduce the stiffness and ultimate load, but increase the failure displacement. The results provide an important theoretical basis for the structural optimization of composite laminates.

This study explores additive manufacturing of carbon fiber-reinforced thermoplastic composites using the Composite-Based Additive Manufacturing (CBAM) process. Carbon/Nylon 12 and Carbon/PEEK composites were fabricated and evaluated through mechanical (compression, tensile, flexural, and impact) and thermal (DSC and TGA) tests. Carbon/PEEK exhibited superior mechanical performance, with 97.5% higher tensile strength, 79.8% higher elastic modulus, and 59.6% higher flexural strength compared to Carbon/Nylon 12. Thermal testing showed that Carbon/PEEK had higher thermal stability, beginning degradation at 350 °C versus 298 °C for Carbon/Nylon. These results indicate that CBAM-fabricated Carbon/PEEK composites are suitable for applications requiring high strength and temperature resistance.