AE monitoring for control of carbon-carbon pyrolysis

Abstract

A capability has been developed for monitoring the AE (acoustic emission) activity in carbon-carbon composites during pyrolysis. Small flat sheets of 2-D woven laminates heated at factory-representative (slow) rates exhibit two stages of intense activity. The first occurs during carbonization, and the second during cool-down. In both cases the emission amplitudes are fairly low and apparently result from microcracking within the matrix and between the matrix and fibers. The driving stresses during heating are due to gas pressure, matrix shrinkage, and thermal expansion. The cool-down emissions are presumed due to thermal stresses. It was possible to force delaminations to occur by rapid heating. Delaminations generate easily identifiable large-amplitude, long-duration emissions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>