J-integral analysis of the mixed-mode fracture behaviour of composite bonded joints

Abstract

ABSTRACTTo increase the confidence in the design of adhesive structures, it is important to be able to accurately predict their strength and fracture properties (e.g. critical strain energy release rate in tension, JIC, and shear, JIIC). Since in most cases the applied loads induce mixed-mode crack growth, it is highly relevant to address fracture under these conditions. This work presents an experimental study using the Single-Leg Bending (SLB) test on specimens bonded with three adhesives, to study and compare their mixed-mode fracture properties. For this purpose, the J-integral method was applied to estimate the tensile (JI) and shear fracture energy (JII). Framing the obtained values in several fracture envelopes enabled to select which power-law failure criterion is more appropriate for each adhesive. Moreover, the tensile and shear cohesive zone model (CZM) laws were obtained for each adhesive by the direct method. Overall, a very good agreement on the fracture properties was obtained between specimens of the same adhesive. The CZM laws for each adhesive also showed a good correspondence between specimens, resulting in a novel methodology for integrated mixed-mode material characterization of structural adhesives for possible use to design adhesive joints.