MIXED-MODE-I, MIXED-MODE-II, AND MIXED-MODE-III FRACTURE CHARACTERIZATION OF ADHESIVE JOINTS

This paper examines mixed-Mode I-II-III fracture of adhesive joints us ing a new experimental method. The expressions used for the average en ergy release rate in Mode I, Mode II, and Mode III along the idealized straight crack front of a cracked, generalized adhesive sandwich are based on beam theory, the J-integral and a beam-on-elastic foundation model. Fracture experiments were performed with adhesively bonded, obl iquely-loaded, equal adherend, split-cantilever-beam (SCB) specimens o f different widths and loading angles, using two different adhesives. It was seen that the fracture surface had an arrowhead shape for small loading angles (similar to that of SCB-type specimens), and a thumbna il shape for larger loading angles (similar to that of double-cantilev er-beam (DCB)-type specimens). Moreover, a sharp step was observed in the thickness of the residual adhesive half-way across the specimen wi dth. When no Mode I was present, the effect of a Mode II loading compo nent on the critical energy release rate G(C) was different from the e ffect of Mode III for one epoxy, but was the same for the other. The a ddition of Mode I caused the effect on G(C) of Mode II to be similar t o that of Mode III for both adhesives.