۱- Introduction

۲- Experimental details

۳- Results and discussion

۴- Conclusions

References

Abstract

This paper presents the influence of the off-axis angles on the flexure behaviors of three-dimensional (3D) woven carbon/epoxy composites. Four kind of samples with different angles, 0 degree, 30 degree, 45 degree and 90 degree, are experimentally tested via three-point bending method. The immersion focused ultrasound imaging and micro-computed tomography (Micro-CT) techniques are employed to investigate the deformation and damage mechanisms in the specimens fractured in bending. Results indicate that the stress-deflections of on-axis (0 degree and 90 degree) samples exhibit obvious quasi-brittle behaviors, whereas those of off-axis (30 degree and 45 degree) samples show important ductile features. Furthermore, the dominant failure mechanism of on-axis samples are identified to be inter-ply delamination and fiber bundle fractures, whereas those of off-axis samples are matrix cracks and tows debonding.

Introduction

۳D woven preforms and their composites as structural components are being used increasingly for the aircraft and space applications owing to their excellent out-of-plane properties for delamination resistance and impact damage resistance [1-3]. In the past few years, researchers have mainly focused on the in-plane mechanical behaviors, while the bending large-deformation and failure mechanisms are still systematically unclear. This can be attributed to the variability and complexity of the microstructure, and the limitation of the experimental technology. Furthermore, 3D woven composites are highly anisotropic, leading to the obvious orientation-dependence. In practice, 3D woven composite materials acquire the load carrying capacities not only along the two principal directions coinciding with the warp and weft axes, but also along any other bias directions. Consequently, an improved understanding of the off-axis bending behaviors and failure characterizations of 3D woven composites will be helpful for researchers in designing and constructing the high-performance materials.