Applied Composite Materials最新文献

Dynamic axial crushing tests were performed on C-section carbon fiber reinforced polymer (CFRP) composite stanchions used in sub-cargo area of aircraft to evaluate their dynamic response under high-speed axial crushing load. A numerical model based on the continuum damage mechanics (CDM) was developed, with calculated failure modes and crushing loads closely matching experimental results, validating the model’s accuracy and reliability. The influence of equivalent axial stiffness and lay-up sequence on the crushing failure modes and energy absorption characteristics of the stanchions was investigated. A mathematical relationship among the specific energy absorption (SEA), average crushing load and equivalent axial stiffness was fitted. The results showed that, compared to single lay-ups, hybrid lay-up configurations exhibited superior structural stability and energy absorption performance. In particular, lay-up configurations with higher equivalent axial stiffness significantly enhanced both the SEA and average crushing load. Furthermore, when the equivalent axial stiffness was held constant, variations in lay-up sequence had a relatively minor effect on the energy absorption characteristics. However, if the axial stiffness of the outermost plies was significantly reduced by consecutively placing 90° plies on the outermost plies, the axial stability of the stanchion deteriorated rapidly, leading to a pronounced decrease in its energy absorption performance.

Honeycomb structures have garnered significant attention due to their outstanding mechanical properties, including high strength, high stiffness, and excellent energy absorption capabilities. This paper innovatively incorporates circular arcs and support structures based on the configuration characteristics of positive and negative Poisson’s ratio cells, designing three novel circular arc honeycomb configurations and their combination forms. Specimens were fabricated using FDM technology. Through uniaxial compression and three-point bending tests, the quasi-static compression and bending properties of these structures were systematically investigated. Finite element simulations provided in-depth insights into deformation mechanisms and stress evolution during compression. Results indicate that the negative Poisson’s ratio with arc and support structure exhibits superior compressive performance, achieving a compressive ultimate strength of 2.6 MPa and a specific energy absorption of 3815.9 J/kg. Compared to conventional honeycomb structures, the specific energy absorption value increased by 3.15 times. Finite element analysis indicates that the arc design effectively disperses stress and enables stable progressive folding. With its high specific strength (6.9 MPa·cm³/g), the negative Poisson’s ratio structure with arcs is suitable for lightweight applications. Bending test results show that the positive Poisson’s ratio arc structure exhibits the highest average crush force (249.1 N) and specific energy absorption (158.8 J/kg) due to arc-induced shear stress dispersion. Combining the three unit cells enhances the mechanical properties of individual cells, with the failure sequence of the composite structure following the strength gradient of the unit cells. This study achieves synergistic optimization of lightweighting, load-bearing, and energy-absorption performance through structural innovation combined with additive manufacturing technology. It provides valuable reference for structural design and application in aerospace, transportation, and building protection fields.

This work examines the joining performance of metal-polymer composite single-lap joints (SLJs) enhanced with 316 L stainless steel Z-pins manufactured through fused filament fabrication (FFF). The Z-pin arrays and steel substrates were co-printed using FFF, and then subjected to debinding and sintering processes. The resulting structure was subsequently combined with polyphenylene sulfide (PPS) through an injection molding direct joining (IMDJ) process to create durable 316 L-PPS composite SLJs. The results show that incorporating FFF-fabricated Z-pins significantly enhance the joining performance of metal-polymer SLJs. A detailed investigation into the effects of pinning density and Z-pin alignment on polymer melt behavior and joint performance revealed that higher pinning densities and vertically aligned Z-pins (90° angle) resulted in superior joint strength. This configuration enhanced PPS melt flow, minimized interfacial defects, and achieved the highest shear strength—improving by up to 113.1% compared to unreinforced joints. The improved mechanical response is primarily due to the Z-pins’ ability to dissipate energy through mechanisms such as interfacial sliding and localized deformation, which hinder crack initiation and growth. This study presents a distinctive strategy for engineering metal-polymer composite joints, enabling the fabrication of multifunctional hybrid structures with enhanced performance.

Conventional honeycomb structures face problems of local buckling, brittle fracture, and insufficient energy absorption efficiency under out-of-plane compression. To address these limitations, this study investigates a bio-inspired spiderweb-like honeycomb structure using 3D-printed short carbon fiber reinforced nylon composite. Specimens of spiderweb-like and conventional hexagonal honeycomb structures were fabricated via fused deposition modeling technology. Through quasi-static compression tests and finite element simulation, deformation modes and energy absorption characteristics of different honeycomb structures were comparatively analyzed. Results demonstrate that the spiderweb-type honeycomb structure achieves significant improvements in load-bearing capacity and energy absorption efficiency through hierarchical collapse mechanisms and coordinated deformation of multiple plastic hinges. Compared to conventional hexagonal honeycombs with equivalent wall thickness, the spiderweb structure exhibits 221% greater load bearing capacity and 94% higher specific energy absorption. When compared to conventional hexagonal honeycomb structures with the same area density, the spiderweb honeycomb shows a specific energy absorption increase of about 35% and a total energy absorption increase of 93.9%. Additionally, parametric studies reveal that hierarchical design parameters r (the ratio of the side lengths of the inner and outer honeycomb layers) in the spiderweb structure plays an important role in the distribution of plastic hinges and plateau stress. When r is in the range of 0.4 to 0.6, the structure achieves uniform stress distribution and maintains high load-bearing capacity through anti-symmetric buckling and progressive folding deformation. However, when r = 1 or r < 0.4, the structure undergoes global buckling or brittle fracture, leading to a decrease in energy absorption performance. This work develops a design framework for bio-inspired hierarchical composites with tailored energy absorption performance, demonstrating specific parameter configurations that achieve superior energy absorption for aerospace and automotive applications.

This study developed four different T-joint configurations: simple hybrid T-joints combining 3D printed polylactic acid (PLA) or carbon-fiber-reinforced PA12 (PA12 CF) with carbon fiber reinforced polymer (CFRP) laminates, as well as two additional T-joint configurations reinforced with carbon fiber overwrap layers. The four T-joint types were systematically evaluated through quasi-static monotonic tensile and shear tests, coupled with finite element simulations using the continuum damage mechanics and cohesive zone modeling. Experimental results show that the carbon-fiber-overwrapped 3D-printed PLA T-joint (PLA-O-T-joint) achieved maximum tensile and shear loads of 3548.9 N and 5625 N, respectively, whereas the carbon-fiber-overwrapped 3D-printed PA12 CF T-joint (PA-O-T-joint) exhibited the highest tensile and shear stiffness values of 799.2 N/mm and 1308 N/mm, respectively. Although PA12 CF itself outperformed PLA in terms of strength, stiffness, and ductility, when joined with CFRP laminate, PLA exhibited better interfacial bonding with the laminates. Failure mode analysis indicated that the carbon fibre overwrapped (O-type) joint method effectively enhanced load transfer, shifting the failure mode from interface debonding to fracture of the 3D printed web, thereby improving damage tolerance. Numerical simulations were consistent with experimental findings, with multiple Hashin failure parameters in the PA-O-T-joint reaching critical values, revealing a coupled failure mechanism involving fibre breakage and matrix cracking. This study highlights the excellent adhesion behaviour between PLA and epoxy resin, as well as the broad application potential of PA12 CF-based hybrid structures in engineering. Adhesion performance can be further improved through interface-enhancing co-curing design concepts and optimisation of overwrap carbon fibre layers, to meet the requirements of lightweight and high-strength composite structures.

In-situ consolidation (ISC) is a highly efficient and cost-effective technology that holds great promise for the manufacturing of thermoplastic composite structures. However, the use of localized heating during ISC inevitably introduces significant temperature and strain gradients. Accurate measurement of temperature and strain using fiber Bragg grating (FBG) sensors is essential for process optimization and control. Yet, the rapidly evolving and highly non-uniform thermal fields present in ISC pose substantial challenges to the decoupling of temperature and strain signals in FBG sensing. In this paper, a novel proxy-point decoupling method for multipoint temperature and strain monitoring is proposed. In this method, based on the premise of spatially repeatable temperature histories along the layup path, temperature data acquired at a remote point are used to compensate strain values at a nearby location, for the first time, enabling online, multipoint, and simultaneous monitoring of temperature and strain both in-plane and through-thickness during the ISC process. We refer to the points used for acquiring temperature data as proxy-point. Building on this approach, the study investigates the through-thickness distributions of temperature and stress, analyzes the residual strain in the manufactured components, and reveals the evolution mechanisms of temperature, stress, and strain during ISC process. The deformation behavior of the composite structures is further elucidated, offering technical references for temperature control in ISC processes.

Automated fiber placement (AFP) enables the efficient fabrication of fiber-reinforced composites. However, the complex geometries of aircraft components often require fiber directions with variable angles, complicating the simultaneous satisfaction of three key manufacturing constraints in AFP path planning: path alignment, path parallelism and path curvature. To address it, a field-based partition framework is developed via singularity construction. First, the vector heat method smooths fiber directions to reduce geodesic curvature. Then, benefiting from the singularities that are constructed by eliminating the vector curl, the ply surface is partitioned from the singularities into patches with improved parallelism of each patch’s vector field. The final laying paths are generated on each partition by parallel offsetting the initial path that comprehensively considers fiber directions over the partition. Compared with the exiting path planning strategy, the proposed method finds higher-quality tow paths with enhanced fiber alignment, lower curvature, fewer partitions and full tow coverage, providing a new paradigm for AFP path planning on complex surfaces.

Foam sandwich structures are widely used in the aerospace, transportation, defense industries and architecture due to their exceptional mechanical properties and physical characteristics. However, the impact resistance of these structures is significantly affected by their sandwich core. In this study, three types of foam sandwich panels were fabricated using uniform multi-layer foam, positive-density-gradient foam, and negative-density-gradient foam as core materials. The effects of core density distribution on the failure morphology, energy absorption characteristics, impact resistance, and damage evolution process of sandwich structures were systematically investigated through drop-weight low-velocity impact tests at energy levels of 20 J, 40 J, and 80 J, combined with finite element numerical simulations. The results indicate that the three specimen types exhibit fundamentally similar failure modes. Under equivalent impact energy conditions, the negative-density-gradient foam sandwich structure demonstrates optimal impact resistance. The positive-density-gradient and uniform-density specimens display progressive failure characteristics during impact damage propagation. In contrast, the negative density-gradient structure manifests face sheet and upper foam layer load-bearing failure, while the underlying low-density foam undergoes plastic deformation, with both synergistically resisting the impact load. The findings of this study provide a theoretical foundation for the design and optimization of impact-resistant sandwich structures.

In this work, the tensile failure mechanisms of 48 K large-tow carbon-fiber-reinforced composite notched structures are systematically investigated through integrated experimental and numerical approaches. Two layup configurations, [-45/0/45/90]_S and [0/90/0/90]_S, with varying notch diameters (0, 4, 8, 12 mm), are experimentally characterized using DIC and microscopic techniques. A macro-meso coupled finite element model integrating Hashin and Gu criteria is developed to analyze stress distribution, damage progression, and failure modes. Experimental results reveal that the [0/90/0/90]_S laminates exhibited higher ultimate strengths but pronounced nonlinearity due to 0° layer dominance, while [-45/0/45/90]_S laminates demonstrated crack bifurcation and interlayer delamination under shear-axial coupling. Notch diameters significantly influenced failure modes: smaller apertures triggered localized 0° yarn fractures, whereas larger notches induced multi-crack coalescence and strain field “spindle-shaped” distributions. The simulation model achieved prediction errors below 9.63% for stiffness and 9.29% for strength, validating its accuracy in capturing interlaminar interactions. Macro/meso fracture analysis confirms fiber-matrix debonding and matrix crushing in ± 45° layers, highlighting the interplay between notch geometry and mesoscale defects. These findings provide critical insights for optimizing large-tow composite joining designs in marine and offshore engineering applications.

This paper investigates the effect of exposure of glass fiber reinforced plastic (GFRP) laminates with epoxy resins to air and a synthetic poly-alpha-olefin (PAO) oil at 180 °C for 500 h (h) and 1000 h. The test is intended for prequalifying material systems for the intended use of the laminates as a composite seal of a stator lamination to enable a directly cooled electric motor. Three commercially available amin curing and one non-commercial anhydride curing epoxy resin systems are investigated. The results of the mechanical testing indicate post curing effects for the epoxy resins during exposure. These translate to higher moduli in the laminates and for most systems the strength rises as well. These effects dominate the change in mechanical properties for the commercial systems making these systems well suited for the intended use case. However, for one commercial and the noncommercial system, some properties drop after exposure to cooling fluid (CF) e.g. in the transverse tensile test. Here a decrease of the fiber-matrix adhesion is the identified cause. This in turn is caused by a moderate laminate quality which is evident by visible imperfections of the laminate. Thermal properties are mostly affected by the chosen temperature and time of exposure, not so much by the ambient medium. From our findings we conclude that the exposure to PAO oils of the chosen systems is not as severe as the findings from other authors suggest. Therefore, the investigated laminates are prequalified for the intended use. In addition, through the successful subsequent use of our results, we find, that the identified test is suitable for prequalifying GFRP for the use in directly cooled electric motors.

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