Characterization of subsurface damage in ceramic‐matrix composites by confocal scanning laser microscopy

Abstract

SUMMARYThe techniques of confocal scanning laser microscopy (CSLM) and reflected‐light microscopy (RLM) have been combined in a study of the subsurface damage in continuous‐fibre reinforced ceramic‐matrix composites (CMCs).The damage was induced by subjecting a composite to Vickers hardness indentation tests and single‐particle impacts. The subsurface damage was viewed conventionally by RLM at specific depths, following material removal by standard metallographic techniques. Mechanical sectioning, however, is time‐consuming and may introduce artefacts in the crack patterns. Consequently CSLM was employed to provide a rapid, non‐destructive analysis of the subsurface damage.In the classic description of elastic‐plastic indentation of monolithic ceramics, there are two major types of crack: radial cracks, which grow out from the elastic‐plastic boundary perpendicular to the surface, and lateral cracks, which are on planes approximately parallel to the surface. In CMCs radial cracks were found to be restricted to the near‐surface region. Lateral cracks, however, were located a few micrometres from the free surface.Preliminary analysis of damage about impact sites by mechanical sectioning and CSLM has shown that the crack patterns are similar to those observed in indentation fracture. The topographical‐mapping facility of the CSLM has been used to detail the radius of damage about an impact site, which has been found to increase with increasing impact velocity.