Development of a simple mixed-mode fracture test and the resulting fracture energy envelope for an adhesive bond

Abstract

Characterizing the fracture energy of bonded adhesive joints over a range of mode mixities often requires special fixtures or a variety of test configurations. By pairing a tapered and a constant thickness adherend, a hybrid double cantilever beam (DCB) specimen is proposed. This asymmetric tapered DCB configuration can be used to determine the fracture energy as a function of mode mixity. As the debond propagates, the relative stiffness of the adherends varies in a systematic manner, resulting in a range of mode mixities from 0° to approximately 20°. Strain energy release rates were obtained using corrected beam theory and a finite element fracture analysis. Single-leg bending tests were used to determine the fracture energy at mode mixity up to 56°. Constant thickness and tapered DCB tests were used to determine the mode I fracture energy. The resulting fracture envelope was constructed in order to show the dependence of the fracture energy on mode mixity for a two part acrylic adhesive.