Numerical analysis of indentation-induced cracking of brittle coatings on ductile substrates

Cracking of hard coatings during indentation is studied using the finite element method. The coating is assumed to be linear elastic, the substrate is elastic-perfectly plastic and the indenter is spherical and rigid. Through-thickness cracks are modeled using cohesive surfaces, with a finite strength and fracture energy. The interface between the coating and the substrate is also modeled by means of cohesive zones but with interface properties. The primary potential locations for the initiation of coating cracks are the coating surface close to the contact edge and the coating side of the interface in the contact region, where high values of tensile radial stress are found. Circumferential cracks are found to initiate from the coating surface and to propagate towards the interface. The initiation and advance of a crack is imprinted on the load-displacement curve as a kink. The spacing between successive cracks is found to be of the order of the coating thickness. The influence of other material and cohesive parameters on the initiation of the first crack and spacing between successive cracks is also investigated. (C) 2002 Elsevier Science Ltd. All rights reserved.