Characterization of the Fatigue Damage of Advanced Ceramic Composites by Scanning Acoustic Microscopy

Abstract

In this report we demonstrate the use of the scanning acoustic microscope (SAM) for non-destructive characterization of fatigue damage in SiC fiber composites. Four continuous fiber ceramic composites (CFCC) samples, subjected to fatigue damage, were studied by scanning acoustic microscopy. The damaged samples were inspected by the high-frequency Ernst Leitz Scanning Acoustic Microscope (ELSAM) and the lowfrequency time-resolved acoustic microscope developed at the Institute of Biochemical Physics (IBCP), Moscow. It has been demonstrated that the high-frequency microscope provides a powerful means of detecting subsurface cracks in composite matrix. In a previously published paper (Manghnani et al. 2000), the low-frequency acoustic microscope was chosen to study the internal fatigue damage in samples without any preparation for SAM investigation. The surface of the fiber sample was rough because of the thick fiber bundles breaking at the surface. It was shown that internal cracks (several millimeters in length) propagated parallel to the sample surface and could be detected by the time-resolved acoustic microscope (Manghnani et al. 2000). In this report we show that a small subsurface crack of several millimeters in length becomes visible after polishing the sample surface. Most of the observed cracks run perpendicularly to the bundles of fibers. Samples with different fatigue loading cycles were thus investigated with SAM, and findings are presented here.