Flexural damage behavior of carbon fiber three-dimensional braided composites using acoustic emission and micro-CT

Some factors such as braiding architectures and braiding angles may cause differences in the damage mechanism of three dimensional braided composites. To address this issue, the damage evolution and deformation process of three dimensional (3D) four-directional (4D) and three dimensional (3D) five-directional (5D) braided composites are detected by digital image correlation (DIC) methods and acoustic emission (AE) technology under three-point bend loading conditions, respectively. Furthermore, the internal damage characteristics of the fractured composite specimens are observed by micro-computed tomography (mirco-CT). The microscopic damage morphology observed by micro-CT has a good correlation with the distribution characteristics of displacement and strain fields, while peak amplitude and peak frequency distributions of AE signals can explain the whole process of damage evolution of the composites. The AE characteristics, microscopic damage morphology and damage-related out-of-plane deformation of 3D4D and 3D5D braided composite specimens with different braiding angles are compared with each other and cross validated. The results show that 3D5D braided composites is strengthened by adding axial yarns in the braiding direction, so it has higher delamination resistance. In addition to this, due to the degree of orientation of the fibers of the specimen with small braided angle is high, the process of damage is shorter and the deformation is smaller.