Zener's crack and the M-integral

In a pair of bonded solids, the interface may block dislocation gliding. The pileup may cause a crack to nucleate either on the interface, or in one of the solids. The model, proposed by Zener half a century ago, has been analyzed in various forms. This note shows that the energy release rate of the crack can be calculated by an application of the M-integral. Both solids are anisotropic, and the interface is flat. The result leads to a discussion of the crack orientation.