Crack front pinning by design in planar heterogeneous interfaces

The propagation of an interfacial crack front along the weak plane of a thin film stack is considered. A simple patterning technique is used to create a toughness contrast within this perfectly two-dimensional weak interface. The transparency of the specimens allows us to directly observe the propagation of the purely planar crack obtained during a DCB (Double Cleavage Beam) test. The effect on the crack front morphology of macroscopic unidimensional patterns in the direction of propagation is studied. In these weak pinning conditions, the geometry of the front quantitatively agrees with the first order expansion proposed by Gao and Rice (H. Gao and J.R. Rice, J.Appl.Mech., 56:828-838, 1989) which accounts for the effect of the interfacial crack front geometry on the stress intensity factor.