Experimental study on compressive fatigue behavior and failure mechanism of 3D five-directional braided composites

The purpose of this research is to study the fatigue behaviors of 3D five-directional braided composites with different braiding angles subjected to longitudinal and transversal compression loads. Compressive fatigue tests were conducted under cyclic stress ratio of R = 0.1 with frequency at f = 5 Hz to study fatigue characteristics by establishing cyclic creep curves, hysteresis loop curves, peak stress ratio curves. The results show that parameters of braiding angle, load direction and stress level affected the fatigue behaviors of braided composite. With evolution of hysteresis loops, permanent strain increased gradually and deformation resistance ability of composites decreased, damage was further increasingly accumulated, the stiffness degradation characteristics was observed. The failure modes and damage evolution were identified by analyzing the evolving damage processes. Generally, the damages got serious with cracks propagation, matrix cracking, fibers breakage, interface debonding between fibers and matrix, which finally resulted in the structure damage.