Abstract:

Objective Three-dimensional(3-D) woven fabric is an fabric structure wherein the upper and lower layers of fabric are interconnected using warp or weft yarns to form an angle interlock structure. Due to their exceptional mechanical properties, 3-D woven composites have gained increasingly popularity in aerospace and military applications. While most research has focused on the failure mechanism of angle interlock woven composite (AIWC) under dynamic load, it is crucial to also consider the various loads that AIWCs endure in practical engineering applications, partications in quasi-static environments. Although the quasi-static load is implicit, the damage and failure resulting from such load cansignificantly impact materials safety, underscoring the importance of studying the mechanical properties of AIWCs in quasi-static environments.

Method In this study, 3-D woven composites were prepared using the vacuum assisted resin transfer molding (VARTM) technique. Subsequently, their bending and compression properties were investigated through three-point bending and compression experiments. X-ray computed tomography (XR-CT) technology was employed to observe microstructural damage profiles and analyze the failure mechanism of the material.

Results In the three-point bending test, the maximum load on the 3-D woven composites reached 1 108.3 N, the bending strength reached 136.43 MPa, and the bending modulus was close to 20 GPa. The primary failure modes of the material included resin compression fracture on the upper and lower surfaces, fiber layer delamination, and warp yarn tension fracture on the lower surface. In terms of compression resistance in the thickness direction, the 3-D woven composites exhibited favorable pefformance. Under compression load, the material experienced significant shear failure along the 45° direction in the thickness, accompanied by resin fragmentation and wavy delamination in both longitudinal and latitudinal directions. Additionally, compression expansion was observed in the latitudinal section. These phenomena were attributed to the appearance of the shear band, resulting in relative slippage of the resin near the shear band and higher shear loads on the straight weft yarns. The bending sections of the warp and straight weft yarns experienced compression against each other. Ultimately, when the yarns reached their extreme limits, the warp and weft yarn fractured, leading to material failure.

Conclusion In conclusion, this study successfully prepared 3-D woven composites using the VARTM technique. The three-point bending test demonstrated that the bending strength of 3-D angle interlocking woven composites reached 136.43 MPa, with a bending modulus close to 20 GPa, indicating excellent bending performance. The main failure modes of the material were matrix cracking, fiber fracture on the lower surfaces, and delamination. The material exhibited good compression resistance in the thickness direction, with a compressive stress reaching 266.17 MPa. The primary failure mechanism in the thickness direction under compression loads was shear failure. In the investigation of the mechanical properties of 3-D woven composites, several aspects require further observation. Firstly, since the material is composed of different warp and weft yarns, it is crucial to study its mechanical properties in different directions. Additionally, apart from the experimental process, the accuracy of the experiments can be verified through finite element simulations and comparison with experimental results.

Key words: angle interlock structure, composite, angle interlock woven composite, carbon fiber, bending property, compression property, failure mechanism