Fatigue Crack Propagation in Adhesively Bonded Joints

Abstract

Adhesive bonding has become a powerful joining technique during the last few decades. It has many applications in aerospace, automotive and other industries. One of the major advantages of adhesive bonding, compared to riveting or welding, lies in its superior fatigue resistance. In this paper, fatigue crack propagation in adhesively bonded joints is analysed and discussed. Three different bonded joints are considered in this study, namely Double Cantilever Beams, Single Lap Joints and Double Lap Joints. Experimental samples were made from carbon fibre composite substrates bonded with an epoxy adhesive. The joints were tested in constant amplitude fatigue at different loads and plots of load against number of cycles to failure were obtained. A crack propagation law was then derived from the experimental results of the Double Cantilever Beam and implemented in a finite element based predictive tool in order to predict the number of cycles to failure for Single Lap and Double Lap joints subjected to cyclic fatigue loading. The prediction technique is based on numerically integrating the crack growth law along the bonding line from an initial crack length to a final crack length. A comparison of mode I strain energy release (G(I)) and total strain energy release rate (G(T)) as failure criteria in the prediction procedures is presented.