Application Of Acoustic Emission Technique In Damage Inspection Of Braided C/SiC Composite

The acoustic emission technology (AE) was used to investigate the damage mechanism of C/SiC composite under tensile tests. The tensile and load /unload /reload tensile tests of single fiber bundle, 2-D woven and 3-D braided C/SiC composites were performed. AE characteristic parameters and waveforms were collected over the entire stress/strain curve. AE characteristic of C/SiC composite damage evolution was analyzed using multi-parameters analytical method, features of C/SiC composite damage evolution were also found. Spectrum analysis was performed to determine the micro-mechanism of damage evolution of C/SiC composites. A damage model was applied to describe the C/SiC composite damage with AE relative energy, and a damage criterion was present for the C/SiCs.Experimental results indicate that:The AE characters of single bundle, 2-D woven and 3-D braided C/SiC composite are different because of their different structures, damage mechanisms and developing progress, which can be verified by micrographic examination on specimens' initial state and fractography.AE accumulative relative energy is related to the damage evolution of C/SiC composites closely. Especially for 3-D braided composites. Damage process includes two main stages: damage initiate period and badly damage period. The spectrum analysis shows different frequency characteristics for different damage patterns of C/SiC composite. And through all the damage process, many damage modes co-exit, never in a pure mode.. Damage evolution equations in the tensile process were formulated, using AE accumulative relative energy as a damage variable, based on single bundle model, average rod model and volume-averaged model, for single bundle, 2-D woven and 3-D braided C/SiC composites respectively. Modification factors were given according to the relationship between elastic modulus reduction and tensile stress. The empirical elementarily formulas of damage evolution in tensile loading were given quantitatively, and verified by experiments.