Effects of residual stresses in the blister test

An analysis of the blister test, which is used as a method for measuring the fracture toughness of interfaces, is presented. The fracture toughness has been determined as a function of the critical loads needed to cause delamination. In most thin-film composites, residual stresses are present and the effect of these is incorporated in the analysis. For isotropic materials with equibiaxial residual stresses, and a pressure or a point load applied to the film, the fundamental shape of the delamination is circular due to symmetry. Closed-form solutions for the energy-release rate and mixedness of modes have been derived for circular crack fronts. One effect of compressive inplane stresses is a possible loss of stability of the circular crack front. Numerical results for the combinations of normal loads and residual stresses which result in crack front instabilities have been obtained and compared with experimental observations. © 1993.