Interface cracking phenomena in constrained metal layers

The deformation in thin ductile metal layers bonding elastic adherends is constrained. This constraint produces stress distribution with a large component of hydrostatic tension, such that the normal stress on the interfaces can greatly exceed the tensile flow strength of the layer material. The interaction of such stress fields with small incipient interface cracks is studied in this paper. Three models are analyzed: (a) pre-existing stationary cracks, (b) cracks which ''nucleate'' on a pre-loaded interface, and (c) cracks which grow along the pre-stressed interface, shielded by a thin plasticity free region. A striking feature is a highly selective size dependence of the cracking process. A crack having a diameter roughly one half the layer thickness experiences significantly higher loading intensity than either larger or smaller cracks. This feature is related to recent experimental observations on interface debonding at thin ductile layers. Copyright (C) 1996 Acta Metallurgica Inc.