Failure process identification in C/SIC samples with a range of tensile performance using acoustic emission

C/SiC composites are important hot-structural materials for future aeronautical applications. However, due to the complexity of the processing method and microstructure, C/SiC often displays a varied mechanical performance. To identify the failure processes of C/SiC made of different size fiber bundles under mechanical load, acoustic emission (AE), an effective continuous damage monitoring technique, was used to monitor tensile tests of C/SiC composites. Combined with the SEM observation on the fracture surface, five damage mechanisms were identified, and their evolution was described. It was found: (1) the main damage mechanisms of C/SiC prepared by the precursor impregnation-pyrolysis (PIP) process under tensile load are matrix cracking, fiber cluster fracture, and fiber cluster pull-out friction; (2) the size of fiber bundles makes the distribution of matrix defects in fiber bundles vary greatly, which has an important influence on the macroscopic properties and damage evolution process of materials; (3) for the C/SiC composites with a lager fiber bundle, lots of matrix cracks appear in the matrix in the fiber bundle at the early stage of loading, which leads to the decrease of material stiffness, in the later stage of loading, the large energy damage such as fiber cluster fracture and matrix cracking between fiber bundles appear and increase rapidly, which accelerates the fracture failure process of the material.