Behavior of perforated metal-to-composite joints subjected to tensile loading

Advanced composite materials have many advantages compared to traditional metallic materials including high stiffness- and strength-to-weight ratios, corrosion resistance, damage tolerance, and improved stealth characteristics. Thus, they are being used more often as primary structural members in both civil and military applications. However these materials are not typically applied in isolation due to insufficient stiffness and ductility of composites compared to metallic materials, leading to a rapid expansion of interests in metal and composite combined structures. The design of hybrid metal-to-composite joints is one of the major structural challenges in this area. Hybrid metal-to-composite joints usually entail both material and geometry discontinuities which lead to stiffness mismatch and local stress concentrations. Current research at the U.S. Naval Academy and Imperial College London shows that among the various types of novel metal-to-composite joints, perforated hybrid steel-to-composite joints demonstrate significant potential in naval structural applications. Perforations are cut into the steel increasing the cohesion between steel and composite part of the hybrid joint thus improving the transfer of load between the two parts. In addition to the benefit of mechanical interlocking, it is believed that the perforated steel plate decreases the elastic mismatch between the stiff steel part and the relatively compliant composite part. This paper reviews an Office of Naval Research - sponsored research project focusing on a perforated metal-to-composite joint design subjected to tensile loading.