Constraint Effect of Adherends on the Fracture of Adhesive Joint (1st report, Microscopic Observation of the Damage Zone around a Crack Tip)

Abstract

The failure behavior around a crack tip in an adhesive joint is important in relation to the integrity of adhesive structures. The bond thickness is one of the important design parameters in adhesive structures. It has been reported that the fracture toughness of a crack in an adhesive joint depends on the bond thickness. However, the mechanism of the dependence has not yet been elucidated. In this study, we investigate the bond thickness effect on the fracture toughness of adhesive joints using a microscope. The damage zones around crack tips in adhesive layers with several bond thickness are observed. The distributions of damage zones and the shapes of rubber particles in adhesive layers are observed by an optical microscope. Additional damage zones are observed along the interfaces-between an adhesive layer and two adherends. As the result, the combination of the damage zone around a crack tip and the additional damage zones is related to the variation of the fracture toughness of an adhesive joint with bond thickness.