Trans-scale characterization of interface fracture in peel test for metal film/ceramic substrate systems

In order to describe the interfacial fracture behaviors of the metal thin film with nano- or microscale thickness peeled on the ceramic substrate, a trans-scale mechanics model has been adopted. In the trans-scale mechanics model, both the strain gradient effect and surface/interface effect are considered. In addition, two fracture process models are used in present study, which are the cohesive zone model and the virtual internal bond model. Using the trans-scale mechanics theory and the interface models, the size effect of the interfacial separation strength between the metal thin films and the ceramic substrates is analyzed systematically by using the peel test. The results show that the fracture process zone size could be taken as the indicator of the trans-scale interface fracture characterization. The interface effect should be considered when the fracture process zone size is at the nanoscale, and the obtained interfacial separation strength is much higher than the conventional separation strength. The material length scale parameters of the metal films are determined by comparing the interfacial energy release rate predicted by the scale theories with the experimental results, which shows that the material length scale parameter could be regarded as the size of active plastic zone in the small scale yielding case during the peeling process