Interfacial mixed-mode fracture characterization of adhesively bonded joints

This paper presents an application of fracture mechanics to determine interfacial mixed-mode fracture properties of adhesively bonded aerospace material systems using the numerical and experimental methods. By means of the finite-element results, correction factors were applied to the specimens with different adherends and a polynomial fit was proposed to evaluate the stress intensity factors of a modified version of Arcan specimen with an interface crack subjected to mixed-mode loading. The finite-element analyses of bonded joints were studied using various materials and different crack length along the interface. The interaction J-integral method was used to separate the mixed-mode stress intensity factors at the interface crack-tip under different loading conditions. The mixed-mode fracture toughness tests were carried out using specimens consisting of several combinations of adhesive, composite and metallic adherends over a wide range of loading angles. Stress intensity factors and associated energy release rates were obtained for various cases of interest. The result of fracture toughness tests revealed that the interfacial fracture of bonded joints is strong under the shearing-mode loading but weak to the opening-mode loading. Several criteria for interface fracture under mixed-mode conditions were examined and compared to test results obtained with different adherends specimens.