a1 Materials Science and Engineering Laboratory, National Institutes of Standards and Technology, Gaithersburg, Maryland 20899
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.
(Received July 20 1992)
(Accepted February 10 1993)
p1 Guest scientist on leave from the Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015.