Unified Adhesive Strength Evaluation for Various Geometries and Loading Conditions using the Edge Interface Crack Method

Abstract

In adhesive joints, debonding usually starts from the interface edge due to the singular stress field at the edge. This is the reason why adhesive strength can be expressed as a constant ISSF (Intensity of Singular Stress Field). However, since the singular stress field and the singularity index vary depending on the local edge geometry at the interface end, the ISSF method cannot be applied to such different local geometries directly. In this study, therefore, a fictitious edge interface crack is assumed at the interface end to evaluate the adhesive strength for different local geometries. In this paper, first, the general expression of the SIF (Stress Intensity Factor) of an edge interface crack useful for butt joint are shown. Next, this edge interface crack method is applied to evaluate the adhesive strength of the lap joints when the local geometries at the interface end are different. The results show that the critical SIFs K_1c are almost constant for all local lap edge geometries. Finally, based on the lots of previous experimental results, the critical values of K_1c are compared for butt and lap joints. Then, it is found that the average strength of lap joints obtained by the edge interface crack method is about five times larger than that of butt joints. In this way, the edge interface crack method is shown to be useful for effectively evaluating the adhesive strength with various geometries and loading.