On the scale effect in the thin layer delamination problem

Influence of layer thickness on the stress distribution in the vicinity of a crack tip is examined, taking into account the fact that the conventional stress intensity factor concept becomes invalid if the thickness of the layer is not much more than the size of the fracture process zone. An eigen-problem is considered which is characterized by two asymptotes. The first is a near one; it is formed in a small vicinity of the crack tip in the layer thickness scale. The second asymptote is a far one in the same scale. The regions of validity of these asymptotes are determined and shown to depend upon layer thickness, material parameters and crack tip speed. The complete stress distribution in front of the crack is obtained, as well. Some conclusions are made concerning the stress distribution and energy release rate for the general problem. Mode III crack propagation is considered in detail.