On the bondline thickness effect in mixed-mode fracture characterisation of an epoxy adhesive

Abstract

ABSTRACT In-situ testing as a method for fracture characterisation of adhesives has received increased attention in recent years. Previous studies show that the fracture properties of the adhesive determined by in-situ testings are influenced by the bond-line thickness. In this work, the effect of the bond-line thickness on the fracture properties of a two-component epoxy ductile adhesive under mixed-mode loading is investigated. Double Cantilever Beam (DCB) and Mixed-Mode Bending (MMB) tests with different mixed-mode ratios were conducted. A recently proposed data reduction technique based on the J-integral approach was employed for the determination of strain energy release rate (SERR) of the epoxy adhesive under mixed-mode loading. Results showed that the fracture properties – particularly critical SERR GC- in in-situ testing is not only a function of bond-line thickness but also the ratio of mode mixity. Increase in the bond-line thickness led to an increase in GIC under pure mode I tests up to 40%. However, this trend was not observed under mixed-mode loadings due to the different type of constraints existing in the MMB tests.