Substrate plasticity assumes an important role in the durability of adhesive bonds. The research investigates the effect of plastic deformation on the strain energy release rate. Two systems were considered. The notched coating adhesion test consisted of a single steel adherend coated with a rubber toughened epoxy. The adhesive thickness varied and the specimen was placed in tension. Results showed that the strain energy release rate was somewhat independent of plastic deformation, but that it was often affected by the quality of the initial debond. The second system, the double cantilever beam, consisted of LaRC PETI-5 adhesive sandwiched between two steel substrates. In this case, we varied the adherend thickness and pulled the specimen apart. Due to an inadequate surface treatment, no conclusive results were obtained. However, after an appropriate treatment is found, strain energy release rate values can be calculated and the energy required to plastically deform the adherends will be analyzed.