ON THE SCALE EFFECT IN THE THIN-LAYER DELAMINATION PROBLEM

Influence of layer thickness on the stress distribution in the vicinit y of a crack lip is examined, taking into account the fact that the co nventional stress intensity factor concept becomes invalid if the thic kness of the layer is not much more than the size of the fracture proc ess 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 i s a far one in the same scale. The regions of validity of these asympt otes are determined and shown to depend upon layer thickness, material parameters and crack tip speed. The complete stress distribution in f ront of the crack is obtained, as well. Some conclusions are made conc erning the stress distribution and energy release rate for the general problem. Mode III crack propagation is considered in detail.