EXPERIMENTAL INVESTIGATIONS OF STRENGTH, TOUGHNESS AND FAILURE MECHANISM OF THE METAL/EPOXY/METAL ADHESIVE SYSTEM

In the present research, we carry out a systematical experimental investigations on the strength, toughness and failure mechanism of the metal/epoxy/metal adhesive system. For the case of the aluminum alloy cylinder/epoxy/aluminum alloy cylinder adhesive system, we measure the tensile deformation and failure behaviors, including the dependence of the failure loading on the adhesive layer thickness and adhesive interfacial inclined angle. Through introducing a series of definitions, such as average normal stress, average shear stress, average normal strain and average shear strain, along the adhesive interface, we realize the measurements on interfacial failure strength, and obtain the relationship between the interfacial strength and the interfacial adhesive angle as well as adhesive layer thickness, and we further obtain the failure strength surface, adhesive interfacial fracture energy, as well as the energy release rate for the binding system of the aluminum alloy/epoxy adhesive/aluminum alloy. The obtained results provide a scientific basis for deeply understanding the strength and toughness properties as well as the failure mechanism of the metal adhesive system, and have an important guiding for the optimization design and property evolution of the metal adhesive system. Through present systematic research and analysis, we come to the following conclusions: The tensile failure of the aluminum alloy/epoxy/aluminum alloy adhesive system globally displays the brittle-elastically failure behavior. Failure mode is the fracture along the adhesive interface of adhesive layer. Both failure strength and interfacial fracture energy display the strong size effect when adhesive layer thickness is at hundred micron level. Interfacial adhesive strength increases obviously as adhesive thickness decreases. At critical state the average normal stress and average shear stress are approximately situated at a same circle on the strength failure surface. The interfacial fracture energy decreases obviously as adhesive layer thickness decreases. Both interfacial failure strength and interfacial fracture energy are closely depended on the interfacial adhesive angle.