Revised notched coating adhesion test to account for plasticity and 3D behaviour

Abstract

Specialized polyamide-imide coating on a CuSn10Pb10 substrate, a material combination utilized often in modern bearing applications, is fabricated using the solvent casting method. The coating adhesion is studied using the well-known notched coating adhesion (NCA) test. Conventionally, the critical strain required to cause the debond propagation is determined by visual observation and indirectly linked to measured strain data to calculate fracture toughness. Here, digital image correlation (DIC) is used to systemically study the coating deformations during testing that enables quantitative determination of the instantaneous debond length. With the introduced method, the critical strain to induce the debond of the coating and the propagation of the debond can be determined for non-elastically behaving specimens reliably. The coating’s debond onset is studied with virtual crack closure technique (VCCT) here. The method can take 3D effects into account in detail and provides a sophisticated method to determine the critical energy release rate. Additionally, cohesive zone modelling (CZM) is used to simulate debond progression. Nonlinear stress–strain responses are observed taking place both with the coating and the substrate materials. The results emphasize that the coating plasticity has a remarkable role in the test behaviour which needs to be taken into account in the revised analysis.