RESIDUAL-STRESSES AROUND VICKERS INDENTS

The residual stresses generated by Vickers indentation in brittle mate rials and their changes due to annealing and surface removal were stud ied in 4 mol% yttria partially stabilized zirconia (4Y-PSZ). Three exp erimental methods to gain information about the residual stress field were applied: (i) crack profile measurements based on serial sectionin g, (ii) controlled crack propagation in post indentation bending tests and (iii) double indentation tests with smaller secondary indents loc ated around a larger primary impression. Three zones of different resi dual stress behavior are deduced from the experiments. Beneath the imp ression a crack free spherical zone of high hydrostatic stresses exist s. This ''core'' zone is followed by a transition regime where indenta tion cracks develop but still experience hydrostatic stresses. Finally , in an outward third zone, the crack contour is entirely governed by the tensile residual stress intensity (elastically deformed region). A nnealing and surface removal reduce this crack driving stress intensit y. The specific changes of the residual stresses due to the post inden tation treatments are described and discussed in detail for the three zones.