Effect of thermal residual stress on the crack path in adhesively bonded joints

Mode I fracture behaviour of adhesively bonded double and cantilever beam (DCB) compact tension (CT) joints was studied using a rubber-modified epoxy (Araldite® GY260) as the adhesive. Adherends were prepared from a carbon fibre (CF)/epoxy composite or aluminium alloys. The crack path in the joints was studied based on the sign of the non-singular T-stress ahead of the crack tip by calculating the thermal residual stress in the joints using finite element analysis. The results indicate that the type of adherend materials influence the level of the thermal residual stress in the adhesive layer, which consequently causes different crack paths in the joints, i.e. a uniformly smooth fracture surface in both CT and DCB aluminium joints and a wavy crack growth in the DCB CF/epoxy composite joints. However, the fracture energies of different types of adhesive joints were almost identical to each other for bond thickness t < 0.2 mm, and a somewhat higher fracture resistance was obtained for the CF/epoxy DCB joints with large bond thickness.