Mixed-mode fracture toughness of a structural adhesive by the single-leg bending test

Abstract

To 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 the perception of fracture under these conditions. This work presents an experimental study using the Single-Leg Bending (SLB) test on specimens bonded with Araldite® 2015, to study and compare the 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 the fracture envelope enabled to select which power-law failure criterion is more appropriate for the Araldite® 2015. Moreover, the tensile and shear cohesive zone model (CZM) laws were obtained for the adhesive by the direct method. Overall, a very good agreement on the fracture properties was obtained between specimens. The CZM laws 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.