Applied Composite Materials最新文献

Triangular defects generated during the Automated Fiber Placement (AFP) process in double-curvature composite structures are a common flaw that significantly affects structural mechanical properties. This study systematically investigates the formation mechanisms of triangular defects, examines their various geometries, and analyzes their stacking behavior across different plies in relation to mechanical performance. The goal is to determine the AFP trajectory design strategy to balance the processability of layup and the performance of the structure for the engineering products. The findings indicate that defect geometry has a relatively minor effect on specimen performance. However, the number of defects and their overlap considerably influence structural behavior. Specifically, a 0° triangular defect in the first ply reduces tensile properties by 13.5%, whereas a 3° defect in the same ply decreases tensile performance by 17.5%. Notably, the presence of two overlapping 3° defects results in a 33.5% reduction in tensile properties, and three overlapping 3° defects lead to a 41.3% decline. Consequently, the design of AFP trajectories for composite structures should aim to minimize the occurrence of triangular defects. Moreover, defects in the same orientation across different plies should be staggered to avoid overlap in the thickness direction, thereby reducing the risk of structural failure. In addition, finite element (FE) simulation analysis demonstrates that the deviation between the triangular defect model and experimental results remains within ± 8%, with deviations for single-ply defects below 5%. This simple FE model and test method are considered reliable and can be utilized for trajectory design, triangular defect analysis, and the control of triangular defects in large size composite structures, thereby enhancing defect management in AFP, and promote the engineering project forward.

Evaluating the damage tolerance of CFRP structures with wrinkle defects under impact loading is crucial for safe service of the composite structures. In this study, the impact tests and compression tests after impact on CFRP specimens with two different wrinkle sizes under three different impact energies are conducted. The damage tolerance of CFRP specimens under varying impact energies and wrinkle defects is evaluated through impact response and compression response. The results indicate that, corresponding to the theory, the maximum contact force exhibits significant stepwise increase with the increase of impact energy no matter what kind of wrinkle size. However, it should be emphasized that, under the same impact energy, the effect of the wrinkle size on the impact performance is not significant with the variation rate of the maximum contact force less than 10%. In terms of impact damage, the specimens subjected to higher impact energy exhibit severe delamination, and the effect of wrinkle size on impact delamination under the same impact energy is more significant at higher impact energy. As for the compression response, due to the effect of the impact damage and wrinkle fibers, the impact energy and wrinkle size both have significant effect on the residual compressive strength. Moreover, the wrinkle fibers play a dominant role in the compression failure mode of the specimen, while the impact damage caused by impact energy influences the extent of the compression failure of the specimen.

The carbon fiber needled composite material uses the needled preform as the reinforcing phase and has extremely excellent properties. Current research has revealed the basic relationships among the needling process parameters, porosity, and the properties of carbon fibers. However, these studies have not made in-depth observations of the sliding tendency of fibers between the composites during the needling process, as well as the generation and variation trends of pores. Especially, the research on the needled preform is still far from adequate. The internal structure of the carbon fiber preform is extremely complex. Structural characteristics such as diverse fiber morphologies and random fiber distributions have not been fully studied. In the research on the key structural characteristics inside the preform, there is a lack of an effective means to comprehensively, deeply, and accurately parameterize and characterize the internal structure. This defect prevents us from having an in-depth understanding of the preparation and performance optimization processes of the carbon fiber preform, and also makes it impossible to provide accurate predictions and guidance for its performance in practical applications. In view of this, this study conducts parametric modeling of the needled carbon fiber preform, analyzes the internal structure of the preform and performs parameter characterization, constructs a finite element model to study its needling behavior, studies the dynamic behavior of the fibers inside the preform, and analyzes the influence of density on the needling behavior.

The influence of the stacking sequence on the mechanical behavior of composite laminates is unquestionable, being one of the most important definitions for structural design. Recently, a novel stacking sequence was proposed in the literature, named Double-Double (DD), demonstrating a great homogenization capability and suitability for optimization procedures due to its double-helix characteristic. However, most DD studies are dedicated to unidirectional carbon fiber reinforced polymers (CFRP). The goal of the present investigation is to extend the DD application to woven glass fiber reinforced polymers (GFRP) for the first time. The stiffness equivalence between DD and quadriaxial (QUAD) is derived based on the classical laminate theory, indicating that it is possible to obtain DD and QUAD woven laminates with the same in-plane stiffness. Tensile tests are carried out to demonstrate experimentally the equivalence between DD and QUAD not only considering the stiffness, but also the laminate strengths. An analytical modeling is implemented to evaluate the laminate failure by applying the Hashin criterion, which is compared with the experimental results and achieved reliable estimations. The influence of multiaxial stress states is also discussed in this study, and the results show that the difference between DD and QUAD strengths is not greater than 10%. At last, a parametric analysis of the strengths of DD laminates is performed. The results highlight that, despite it is theoretically possible to define an equivalent QUAD for the DD with the highest strength, it is not applicable in practice because it would require a large number of plies.

The use of ceramic matrix composite (CMC) in blades is crucial for improving aero-engine performance. However, designing complex fiber architectures while considering manufacturing constraints poses significant challenges for blade design and evaluation. Manufacturing constraints specifically refer to fiber continuity constraints and fiber path curvature constraints. Here, a cross-scale design methodology and a static strength evaluation system for CMC blades were established and subsequently applied to the design of shrouded blades. The cross-scale design method adequately considered the variety and differences in fiber-architecture molding methods. Weaving parameters were optimized through a cost-effective, simulation-driven design. The blade performance and structural integrity were balanced under manufacturing constraints. The developed static strength evaluation system was used to compare the performance of different designs through simulation analysis and critical tests. No defect was found in the CMC blade prototypes after holding a load for 2 min at 1.15 times their maximum rotational speed. This demonstrated sufficient static strength and confirmed the effectiveness of the design methodology and evaluation system.

Achieving robust low-resistance electrical contact with carbon fibres embedded in polymeric matrices is a challenge, and different electrode fabrication methods mostly post-curing the composite have been examined in the literature. This paper investigates the use of metallic foils co-cured on the top surface of carbon fibre reinforced polymer (CFRP) composites to form stable electrodes. The effects of different electrode materials and their geometric variations on the interface resistance (IR) between CFRP and electrodes are studied experimentally. Finite element (FE) analysis is used to estimate the spread resistance (SR), providing a reliable measure of IR for various electrode–CFRP configurations. Copper is found to be the optimal electrode material and has a low IR per unit electrode area ranging from 2.5 × 10⁻⁴ Ωmm⁻² to 1 × 10⁻³ Ωmm⁻² independent of geometric parameters. Pull-off tests demonstrate that the co-cured electrodes exhibit acceptable mechanical bonding with the composite layer. Compared to other electrode fabrication methods, the co-curing technique is significantly easier, less invasive and more cost-effective, as it eliminates the need to alter or induce surface damage in CFRP specimens.

Graphical Abstract

Co-cured metal foils simplify electrode fabrication in CFRP and achieves stable, low interface resistance

In this study, an integrated composite antenna structure was designed and fabricated to investigate its behavior under low-velocity impacts with energy levels ranging from 10 J to 100 J. The specimens were positioned and supported in accordance with ASTM D7136 standards, while post-impact compression tests followed ASTM D7137 protocols. Numerical models were developed using ABAQUS finite element (FE) software to validate experimental results, including impact response curves, damage morphologies, and compression failure modes. Both experimental and simulation results demonstrated strong agreement, confirming the accuracy of the constitutive model. Additionally, electromagnetic performance evaluations through experiments and simulations verified the structural integrity and functional reliability of the antenna under varying impact conditions.

Metal matrix composite (MMC) sheets with well-dispersed reinforcements can be continuously produced using the accumulative roll-bonding (ARB) method. However, carbon fibers (CFs), an ideal reinforcement for MMCs, have not been extensively utilized due to the poor wettability of carbon/aluminum system. This study addresses this issue by modifying the fiber surface with copper (Cu) coating and applying this new reinforcement to Aluminum matrix composites (AMCs) produced via the ARB method. The results demonstrate that copper coated CFs (Cu-CFs) were well-dispersed throughout the matrix with appropriate ARB cycles. The surface treatment improved the spatial uniformity of the reinforcement, enhanced interfacial bonding, and refined the matrix grains. Consequently, the Cu-CF/Al composites exhibited the highest tensile strength (187.8 MPa) compared to composites reinforced with uncoated CFs (131.9 MPa) and monolithic Al without CFs (122.7 MPa). These findings suggest that combining ARB with electroless copper coating holds broad prospects in materials engineering, providing a valuable area of study for enhancing composite material performance.

This work aims to assess the potential of commercially available PA 6,6 nanofibrous mats when incorporated to large scale filament winding process. The conventional wet winding process was employed on a specially designed flat mandrel to manufacture uni-directional composite laminates. A49-12 K carbon fibers and cryogenic-compatible CTD 7.1 epoxy resin was employed. The winding process was temporarily paused at the mid-plane thickness to introduce a pre-crack using a 12 μm non-adherent film and to place PA66 nanofibers with an aerial weight of 3 g/m². The winding process then resumed. Laminate curing was performed in an autoclave oven for 3 h at 80^oC under nitrogen environment. Flat wound laminates were then cut into end notched flexure (ENF) test samples in accordance with ASTM D7905/D7905M-19. ENF tests were performed at room temperature (RT) and cryogenic conditions in a liquid nitrogen bath. Test results suggested that mode II strain energy (G_IIc) of interlayered laminates were 35% higher than the one of neat laminates when tested at room temperature. On the contrary, addition of polymeric nanofibrous interlayers reduced G_IIc by 40% in cryogenic conditions. Fractographic analysis suggested that the improvement at RT was primarily due to (i) toughening at the resin rich pockets inherent by the tow-undulation effect in wet winding (ii) crack deflection in irregular tow-tow interfaces. The reduction in G_IIc was attributed to synchrony of several factors, namely dominance of fiber/matrix debonding due to thermal contraction at fiber/resin interfaces, elevated brittleness of the polymeric nanofibers and pre-mature cracking due to nanofiber/resin debonding.

In this paper, an architecture-based approach is proposed to enhance the quasi-static crushing behaviour of trigger-free composite energy-absorbing structures. To validate the proposed methodology, specimens with an inner diameter of 32 mm and a wall thickness of ~ 1 mm were manufactured and tested under axial quasi-static compression (20 mm/min) using a filament winding technique. Two sets of samples were fabricated by including an external CFRP mesh to enhance the hoop strength and promote progressive crushing. By comparing the test results with those of the base material, a remarkable influence of the outer layer on the crash performance (> 50% of the SEA) was registered, despite a negligible increase in weight. Furthermore, since geometric modifications (e.g., edge chamfering) were unnecessary to achieve progressive crushing because of the contribution of the outer mesh, this approach can be further explored to simplify the manufacturing process of energy-absorbing structures.