Investigation of Flexural Progressive Damage of Three-Dimensional Braided Composites by Acoustic Emission and Micro-CT

Three-dimensional four-direction is the most widely used braided structure in the field of three-dimensional braiding. For purpose of improving the mechanical properties of this kind of braiding in a certain direction, three-dimensional five-directional braid has been developed. The aim of this work is to investigate the progressive damage and failure behavior of three-dimensional five-directional braided composites subjected to three-point bending. To comprehensively analyzing the damage process of 3D five-directional braided composites, a variety of non-destructive testing methods is used, involving acoustic emission, digital image correlation and X-ray micro-computed tomography. Among them, the acoustic emission response behavior of the composite damage process is monitored in real time, and the displacement and strain field at different stages are calculated by the digital image correlation method. More importantly, the microscopic damage morphology of the materials is visualized by using X-ray, and the analysis results are supplemented and verified. Through analyzing the experimental results, the obvious Kaiser effect is observed, and the acoustic emission signals are concentrated in the middle and late stages of loading and directly related to the cumulative degree of damage. In addition, the position of the strain and displacement set from the deformation measurement is consistent with the damage evolution from the micro-computed tomography observation.