Stress and energy analysis of toughness measurement for adhesive bonds

Abstract

Fracture toughness of structural adhesives is an important design parameter characterized by the critical stress intensity factor K c or the fracture energy J c . Sandwich-type Double Cantilever Beam (SDCB) specimen is widely used for the measurements of toughness of adhesives. The energy analysis of SDCB, as presently modelled, accounts only for the cantilever part of the adherent which is assumed fixed at the crack tip. The contribution of the adhesive layer to the displacement at the points of load application and thus to the energy balance is ignored. Experiments, however, indicate a strong effect of thickness and elastic properties of the adhesive on the toughness measurement. A model is proposed to account for the adhesive layer. The model analyses adhesive-adherend interaction and expresses the energy release rate in terms of bond thickness, specimen dimension and adhesive-adherend properties. It is shown that the contribution of the adhesive layer to the measured quantity is significant.