Opening-mode fractures of a brittle coating bonded to an elasto-plastic substrate

Abstract

An elasto-plastic fracture model is presented to study the opening-mode fractures for an alumina coating fully bonded to an aluminum substrate undergoing large tensile deformation. The periodic stress field in the coating layer is described by one section between two adjacent cracks. The coating material is brittle and elastic; whereas the substrate exhibits elasto-plastic behavior that is characterized with a bi-linear hardening plastic function. For simplicity, a one-dimensional elasto-plastic model is employed to the substrate; an elasto-plastic shear lag model is used to describe the stress transfer from the substrate to the coating; and a plane strain formulation is derived for stress analysis in the coating. Explicit solutions have been derived for the coating-substrate system under different loading stages. When the applied load is in the linear elastic state, the elastic field in the coating is verified with the finite element results. When the substrate yields, the fracture energy release rate can be calculated and the corresponding elasto-plastic fracture analysis is conducted. Experimental characterization has been further conducted to validate the present model, which in overall predicts the fracture initiation, infilling and saturation in the coating successfully. The present formulation is general and can be applicable to other types of coating – ductile substrate systems.