Characterizing Dynamic Fracture Behavior of Adhesive Joints under Quasi-Static and Impact Loading

An experimental evaluation of the dynamic fracture properties of an automotive epoxy is presented. Pronounced stick-slip behavior was observed in both quasi-static and impact tests of aluminum and composite adherends bonded with this adhesive. An experimental technique for conducting low speed impact of adhesively bonded automotive composite joints is presented. Based on the use of a modified drop tower, mode I, II, and mixed mode values for critical energy release rate were determined to create a fracture envelope for the composite/epoxy system. Because load measurements are erratic and unreliable at higher test rates, displacement-based relationships were used to quantify these energy release rates. Displacement data were collected with an imaging system that utilizes edge detection to determine displacement profiles, end displacements, and opening displacements where applicable. Because of the resolution of the image-based approach being used, determining crack length experimentally is difficult. As a result, numerical methods based on edge detection algorithms were developed to objectively determine the crack length based on the available experimental data in mode I, II, and mixed mode I/II configurations.