Indenter/coating modulus mismatches and load location effects on contact damage in curved brittle-based bi-layer structures

This paper summarizes some of the recent advances that have been made as a result of contact damage tests on bi-layer structures containing one brittle layer on a polymeric support base. The effects of indenter modulus (hard/soft indenters) and of the sate of loading (load location reference to the specimen axis of symmetry) on contact damage in bi-layer systems were investigated. Convex specimens having curvature of 12 mm inner coating diameter and 1mm thick were produced, and loaded along the axis of symmetry and off axis at 45o using flat indenters of six different moduli. The influence of indenter modulus on radial crack initiation and damage evolution was examined in respect to the load location, with particular attention paid to the relevance of such damage to lifetime-limiting failures of biomechanical layered systems. The results of this study illustrates that the fracture behaviour of brittle layered structures is not dominated by certain parameters. Critical loads for initiation of radial cracks are sensitive to indenter modulus (hardness) but not sensitive to load location. Load location plays an important role in crack propagation and subsequent damage patterns, especially at specimen margins.