ABSTRACT
Two types of radial cracks are generated at indentations in Y-TZP materials. These are “trapped” cracks within the contact-induced transformation zone surrounding the indentation impression and “well-developed” cracks which extend beyond the transformation zone boundary. The probability of generating a well-developed versus a trapped crack is dependent on the transformability of the material (determined by the stabilizer content and grain size) and on the indentation load. The effect of applied stress on well-developed and trapped cracks is investigated by in situ measurements of crack size as a function of a superimposed bending stress. Well-developed cracks grow in stable equilibrium to failure. Weakly trapped cracks escape from the contact-induced transformation zone to well-developed form at high stresses, and exhibit stabilized growth before failure. Strongly trapped cracks do not pop in to well-developed form, but fail spontaneously.
