A study of environmental attack effects on the bonding strength of an epoxy adhesive by using small column shear tests

Abstract

Epoxy resins, one of the high-performance polymer materials, have been widely used as an adhesive because of their excellent strength and durability due to their cross-linked network structure. It is necessary to understand the adhesion mechanism to ensure their reliability as structural adhesives. It is concerned that environmental attacks, such as high temperature and humidity, degrade the bonding strength of the adhesive structure. In order to understand the degradation mechanism by environmental attacks, it is necessary to evaluate the intrinsic bonding strength of adhesive systems by a quantitative test method. This study proposed a novel test method to evaluate the shear bonding strength using a small columnar resin formed on the metal adherend's surface and investigated the adherend and environmental degradation effects on the bonding strength using the proposed method. The experimental results revealed that the bonding strength of the epoxy adhesive was affected by the environmental attack. The bonding strength increased regardless of the substrate material after the low-humidity and high-temperature exposure. On the other hand, the effect of the high humidity attack on the bonding strength was different depending on the adherend: the bonding strength of SUS304 decreased, on the other hand, that of A5052 increased. The fracture morphologies also changed in the case of A5052 adherend after the high humidity and temperature exposure. AlO(OH) was formed on the A5052 adherend surface after high humidity and temperature exposure, which might have affected its bonding strength.

Keywords

• epoxy adhesive
• bonding strength
• shear test
• environmental degradation
• x-ray photoelectron spectroscopy