A mode I crack parallel to the interfaces in a periodically layered medium

The plane problem of a single crack in a periodically layered bimaterial composite is considered. For the case of a long crack loaded by opening normal tractions, the universal relation obtained between the Mode I and Mode II stress intensity factors show that the most dangerous crack location lies in the midplane of the layer. This crack location of the Mode I finite length crack is examined in detail. A closed form expression of the Green's function for a single dislocation is derived and the problem is reduced to a singular integral equation of the first kind. The study of the dependence of the normalized stress intensity factor upon the crack length reveals a wavy nonmonotonic behavior. A simple analytic formula for the limiting case of a semi-infinite crack is derived. It is found to be valid for a broad range of parameters.