Tensile damage evolution of 2D SiC(f)/BN(i)/(SiC-B4C)(m) composites based on acoustic emission pattern recognition

The tensile test of 2D SiC_(f)/BN_(i)/(SiC-B₄C)_(m), with acoustic emission (AE) online monitoring, was carried out to study the mechanical properties and failure mechanism. Using the pattern recognition technique to find out the relationship between AE signals and damage mechanisms, an improved sentry function was proposed by choosing the AE energy of fiber breakage instead of the AE energy in its definition. Combined with the cumulative trend of each class of the AE signals, the damage evolution process was identified. It is found that the entire loading process includes four stages: (a) the linear elastic stage, there have sporadic AE events; (b) the initial damage stage, the matrix cracking contributes 80.4% of the AE energy and leads to the non-linear behavior of the stress-displacement curve; (c) the damage development stage, in which all types of damage continuously happen; and (d) the damage acceleration stage, dominated by fiber breakage that accounts for 60.1% of the AE energy. The improved sentry function has a decreasing trend during the fourth stage, which provides an early warning before failure, and gives a reliable ultimate strength.