A finite element analysis of stationary crack tip fields in a pressure sensitive constrained ductile layer

Polymeric ductile adhesive layers joining two elastic adherends is a common feature in various technological applications. Such joints can fail by ductile rupture involving interface debonding and void formation. It has been observed that, unlike in metals, the yield behaviour of polymers is affected by the state of hydrostatic stress. In the present study, the effect of pressure sensitivity of yielding on the stress and deformation fields near a stationary crack tip in a constrained adhesive layer is examined. To this end, finite deformation, finite element analyses of a cracked, sandwiched adhesive layer are carried out under plane strain, small-scale yielding conditions for a wide range of mode mixities. The Drucker-Prager constitutive equations are employed to represent the behaviour of the layer. Both dilational and non-dilational plastic flow are considered. It is found that the stress levels in the layer decrease with increasing pressure sensitivity irrespective of mode mixity. The effect of pressure sensitivity on the notch tip deformation, and near tip plastic mode mixity, is also investigated. Finally, theoretical predictions are made about the variation of fracture toughness with mode mixity due to interface debonding. (C) 2000 Elsevier Science Ltd. All rights reserved.