A comprehensive experimental study on bi-adhesive single lap joints using DIC technique

Abstract Stress concentrations at the overlap ends are one of the main reasons for strength reduction in adhesive joints. The bi-adhesive technique was introduced as an efficient solution to reduce the stress concentrations at the overlap ends. Although several works have dealt with the numerical analysis of edge effects in bi-adhesive joints, none of them have experimentally analyzed the strain distribution along the bi-adhesive bondline. Moreover, the interaction of some geometrical parameters on the performance of bi-adhesive joints has not been studied yet. The aim of the current research is to present a comprehensive experimental analysis of bi-adhesive single lap joints using the digital image correlation (DIC) technique. Therefore, two different adhesives (one stiff and one flexible) were selected. Different parameters such as adhesive thickness, substrate thickness and length ratio (length of flexible adhesive at one overlap end to the total overlap length) were considered. Furthermore, the interaction of these parameters were experimentally analyzed using the DIC method. A numerical analysis was also conducted to analyze the effect of length ratio on the strain distribution along the bondline. Based on the results, the failure initiates at the interface between the stiff and flexible adhesives and kinks through the brittle adhesive. DIC results illustrate that the effect of length ratio on the adhesive peel strain increases by increasing the adhesive thickness and decreases by increasing the adherend stiffness.