Contact-induced Damage in Ceramic Coatings on Compliant Substrates: Fracture Mechanics and Design

Simple explicit relations are presented for the onset of com-peting fracture modes in ceramic coatings on compliant sub-strates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near-contact area. The critical load relations are expressed in terms of well-documented material parameters (elastic modulus, toughness, hardness, and strength) and geometrical parame-ters (coating thickness and sphere radius). Data from selected glass, Al2O3 and ZrO2 coating materials on polycarbonate substrates are used to demonstrate the validity of the relations. The formulation provides a basis for designing ceramic coat-ings with optimum damage resistance. I