POSTFAILURE SUBSIDIARY CRACKING FROM INDENTATION FLAWS IN BRITTLE MATERIALS

Vickers indentation sites in ceramics have been examined after specimen failure from median/radial indentation cracks. Evolution of a new cracking pattern of ''ortho-lateral'' cracks, originating at the intact corners of the Vickers indentation and running orthogonal to the classic-lateral cracks and parallel to the new fracture surface, has been observed. In some instances postfailure extension of the classic-lateral cracks toward the surface was also observed. Enhanced residual tensile stress from relaxation of constraints on the indentation-plastic cavity by the generation of a fracture surface is postulated to drive the subsidiary cracking. A simple qualitative model to explain this phenomenon is presented. Possible implications of such postfailure subsidiary cracking on residual-stress-driven flaws, postmortem fractography, and wear in ceramics are discussed.