Progressive damage visualization and tensile failure analysis of three-dimensional braided composites by acoustic emission and micro-CT

Tensile failure and damage visualization based on progressive damage mechanics of three-dimensional braided composites were investigated. The complementary nondestructive testing technology combining acoustic emission with X-ray micro-computed tomography was used to analyze signal parameters, mechanical performance and internal damage morphology. The damage evolution results indicate that progressive damage will result in the reduction of Felicity ratio, stiffness stability and ultimate carrying capacity of specimen. The tightening cracks and load oscillation are the omens of instability failure and catastrophic failure of the specimen respectively. The specimen mainly experiences the initiation and propagation of cracking and debonding but there are multiple damage mechanisms in the failed specimen, which is consistent with the fact that deformation is not obvious until the huge deformation occurring in the final failure. In addition, longitudinal cracks first develop along the path of the least resistance between yarns under low tensile stress, and transverse cracks initiate and propagate along a relatively straight path under high tensile stress. In brief, progressive increasing tensile load can eventually cause instantaneous catastrophic failure to the specimen.