Energy release rate analysis for adhesive and laminate double cantilever beam specimens emphasizing the effect of residual stresses

The mode I energy release rate, including the effect of residual stresses, was evaluated for both adhesive and laminate double cantilever beam specimens. The energy release rate can be partitioned into a mechanical term and a residual-stress term in beam theory. The beam-theory mechanical term is not very accurate, but can be corrected by a slight modification to a previous correction factor. This correction factor accounts for crack tip rotation of the specimen arms. The beam-theory residual-stress term is very accurate for a wide range of specimen geometries; it can be used without correction. The consequence of ignoring residual stresses is that one measures an apparent toughness instead of a true toughness. The error between the apparent toughness and true toughness can be calculated for a given specimen geometry and amount of residual stresses. Such errors can be large and are often larger than the correction required for crack-tip rotation effects. In double cantilever beam specimens used to study laminate delamination, the errors are large when the delaminating arms, considered by themselves, are unsymmetric laminates. Some experimental methods are suggested which can be used to correct for residual stress effects.