THE EFFECT OF RESIDUAL-STRESSES ON THE DEBONDING OF COATINGS .1. A MODEL FOR DELAMINATION AT A BIMATERIAL INTERFACE

An analysis is presented of how a general set of residual stresses is predicted to influence the debonding behaviour of a coating. This is o riented towards relatively thick coatings, in which significant throug h-thickness variations of residual stresses may occur. A through-thick ness deposit crack is assumed to exist and the external loading is pur e bending. An expression for the interfacial strain energy release rat e, G(i), comprised of three terms, due to the applied loading, to the residual stresses and to an interaction term dependent on both, is der ived. An experimental procedure to characterise the residual stress di stribution is described. During interfacial fracture, the crack path, and therefore the loading state at the crack tip, are pre-determined b y the plane of weakness. Since the critical value of G(i) for interfac ial failure has been observed to be a function of this loading state, a procedure is described for determining the phase angle characterisin g it for a given applied load and residual stress state. The results o f these analyses are presented for various generalised residual stress states. In the second part of this pair of papers, the model is appli ed to experimental data for thermally sprayed coatings.