On the transition between adhesive and cohesive modes of debonding during peeling of thin plates bonded with an epoxide adhesive

A transition from an adhesive mode of debonding at low debonding rate to a cohesive mode at high debonding rate was observed when peeling assemblies consisting of thin metallic plates bonded with an epoxide adhesive. Stable cohesive debonding was found to be characterised by a river pattern aspect of the debond surfaces and by an increase of the apparent debonding resistance with increasing debond extension. Mechanisms are proposed for the initiation and extension of cohesive debonding. Second phase nodules in the adhesive are shown to be the sites of nucleation of cavities. Initiation of cohesive debonding is ascribed to the onset of this cavitation, which is promoted by the increase of the adhesive yield strength with straining rate. Cohesive debond extension is analysed in terms of a meniscus instability mechanism whereas the R-curve behaviour is related to the finger-like extension of the debond front.