Crack kinking from an initially closed interface crack

One studies crack kinking from an interface crack when this crack is closed prior to kinking but open after it. Contact is assumed to occur without friction. This problem was considered very recently by the authors in the special case of some homogeneous material (ordinary crack). One establishes the relation between the stress intensity factors just before and just after the kink. From there, and using Goldstein and Salganik's famous principle of local symmetry, one derives the value of the kink angle. This value is somewhat surprisingly found to depend only very weakly on the mismatch of elastic properties between the materials.