The influence of static normal stress on shear capacity of bonded high strength steel interfaces

Incorporating high strength steels in mechanical engineering structures is frequently limited by the relatively low fatigue strength of welded joints relative to the fatigue strength of the base material. Hybrid joints, which combine mechanical fasteners with bonding, provide potential joining alternatives for high strength steel structures. Not surprisingly, a wide variety of mechanical and bonded joints are used in the automotive and aircraft industries where light weight and structural integrity are primary design drivers. For thin sheet metal structures in high strength steel, structural adhesives can effectively increase the maximum service load of friction based non-slip bolted connections. For hybrid joints, mechanical fasteners provide high connection ductility and they effectively hinder peeling failures of the adhesive interface. In addition, structural adhesives are known to improve the load distribution characteristics of a joint resulting in lowered local stress concentration factors and improved fatigue strength. An extensive literature search has shown that relevant design input data are missing. An experimental and analytical research program has been initiated to assess the static and cyclic shear strength of epoxy bonded high strength steel joints subjected to various degrees of static normal pre-stress.