Off-axis bending behaviors and failure characterization of 3D woven composites

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.