Contact damage of curved zirconia/epoxy bi-layers

Abstract

Contact damage of a curved bi-layer system, consisting of a brittle zirconia coating (Y-TZP) on a compliant polymeric substrate from indentation by a hard tungsten carbide sphere is investigated. The specimens are loaded axially at their top surface. The failure evolution and critical loads to initiate radial cracking in curved zirconia/epoxy bi-layer specimens are compared to those of flat bi-layers with the same thickness. The onset of fracture is observed in situ using a video camera. Finite element modelling is used to evaluate the stress distribution in the zirconia coating, and to confirm experimental data. It is demonstrated that in all specimens, cone cracking occurs prior to radial cracking, with the latter being defined as the primary mode of failure. Increasing the curvature has little effect on the critical load to initiate radial cracking, but causes unstable crack propagation towards the extremities of the specimen resulting in catastrophic failure. The results of this study provide useful guidelines from the data trends, and for extending the system to tri-layers.