Fracture behavior around a crack tip in rubber-modified epoxy adhesive joint with various bond thicknesses

摘要

Mechanisms of fracture behavior around a crack tip in the adhesive layer of an adhesive joint are important for understanding and thereafter improving the structural integrity. Bond thickness is one of the significant design parameters for adhesive joints. Many studies on bond thickness dependence of the fracture toughness of adhesive joints have been performed. For example, Bascom et al. [1,2] investigated the tapered double cantilever beam (TDCB) specimens jointed by a rubber-modified epoxy resin adhesive and found that the fracture energy was maximized at a bond thickness equal to the diameter of the plastic (damage) zone formed ahead of the crack tip. Kinloch and Shaw [3] confirmed this effect of the bond thickness on the fracture energy G_(IC) of adhesive joints as well as a considerable role of the damage zone size in enhancing G_(IC). Ikeda et al. [4] conducted the elastic-plastic analysis of the stress field around the crack tip in adhesive joints and showed that a very thin adhesive layer induced the suppression of crack tip blunting and thus a large increase of the stresses within the finite strain zone between rigid adherends, thus caused a decrease in G_(IC). Daghyani et al. [5] presented an experimental result that a decrease in G_(IC) for a thin adhesive layer was due to a transition of fracture process from cohesive resin failure to interfacial adhesive failure between resin and adherend. However, most of the studies hardly considered microstructural aspects in adhesive layers which are needed for better understanding the variation of G_(IC) with the bond thickness.