Acousto‐ultrasonic evaluation of carbon‐carbon composites at different processing stages

Abstract The final form of a carbon‐carbon (C/C) composite is a consequence of a series of complex processing stages, during which significant changes occur in material microstructure and properties (thermal, physical, and mechanical). Owing to the uncertainties in the processing steps, material integrity and quality assurance is a matter of concern. The present study focuses on acousto‐ultrasonic (AU) evaluation of plain and eight‐harness (8H) satin weave fabric reinforced C/C composites. Studies pertaining to ex‐situ AU testing of C/C composites at various stages of processing are presented. The sensitivity of AU in identifying such defects as fiber breakage and misaligned fibers is also considered. AU signatures were interpreted in the time and frequency domains through well‐known approaches, such as measurement of stress wave factor (SWF) and spectral moment computation. The results indicated strong qualitative and quantitative correlations between the parameters obtained from time and frequency domain features of the AU signal and the evolving microstructure of carbon‐carbon at various processing stages. An important application of this work will be in the establishment of AU for in‐situ process monitoring of C/C composites.