Fracture mechanics characterization of composite/metal interfaces of bonded joints

Adhesive bonding between different materials has been widely used for a large variety of applications, such as in the aircraft, automotive, and many other civil engineering structures. Adhesive-bonded joints as load bearing components have the potential to save significant weight and cost over conventional riveted or bolted joints. For the last ten years a major problem in adhesive technology has been the difficulty in predicting the accurate load bearing capacity of a joint. This difficulty comes from the fact that the stress distribution in the adhesive joint is very complex and singular stress field exists at the bi-material corner. And for bonded joints, the failure usually occurs at the adhesive/adherend interface. Therefore another difficulty comes from the complex interfacial failure analysis due to the formation of chemical bonds, whose strengths are difficult to measure. Many studies have been conducted to investigate the effects of bond thickness, material properties of adhesives and adherends, and geometric shape of bi-material corner tip to the fracture behavior of bonded joints. In this paper, we analyze the stress fields at the interface corner of composite/steel(anisotropic/isotropic) double lap joint to predict failure by using stress intensity based fracture criterion. And analytical results are compared with experimental results of co-cured lap joints under tensile load condition. Micro-structural features, hardness characteristics, and fracture toughness determinations of the interfaces are also conducted.