Effects of bondline discontinuity during growth of interface cracks including stability and kinetic considerations

The effects of a single discontinuity/void on the mode I interface crack growth under a constant loading rate are investigated experimentally and analytically. To account for a coexistence of the void and the crack tip process zone, a new unit pattern model is derived. The crack growth path is composed from the three distinctive zones: (1) The initially bonded crack front vicinity region--carrying the majority of the loading--is of finite length and modelled as a series of elastic springs. (2) The discontinuity region is modelled as a simple beam not carrying any surface tractions. (3) The far field is of infinite length and represented with elastic springs. In this model, the constant loading rate boundary conditions are fully considered. Subsequently, the kinetic effects associated with the specimen geometry and the presence of the discontinuity are attempted using the generalized Griffith's theory. A very good agreement between the experimental and the analytical results is observed for both the load response and the R curves for all void-to-process zone length ratios. A new light and a more profound appraisal of the equilibrium paths are gained.