Identification of Failure Modes of Carbon-Carbon Composites at Various Processing Stages Using the Acoustic Emission Technique

Abstract

In the fabrication of carbon-carbon (C/C) composites, the first carbonization process is crucial, as the mechanical properties of the composite are completely altered at this stage. Some predominant effects of this process, in the composite, are development of delaminations, fiber breaks, distributed porosity and formation of transverse cracks in the matrix. These effects are to some extent, beneficial, during latter processing of the composite. However, excessive occurrence of any of these effects is undesirable. Keeping this in view, the present study focuses on the utilization of acoustic emission (AE) (as a nondestructive evaluation (NDE)) technique for identification and characterization of failure modes of C/C composites at several processing stages of C/C composites. Primarily, acoustic emission (AE) has been used to study the failure modes of C/C composites at the as-cured, carbonized and densified stages using AE parameters such as the peak amplitude, event duration and energy content of the AE signals. These parameters have been related to the initiation and progression of matrix cracking, fiber breakage and delaminations which occur in the composite at the as-cured, carbonized and densified stages.