Performance evolution of epoxy adhesive and CFRP-steel epoxy-bonded joints subjected to hygrothermal exposure

Abstract

Carbon fiber-reinforced polymer (CFRP)-steel epoxy-bonded joints are widely used in civil, mechanical, and railway engineering structures. However, the mechanical and bonding performance of the epoxy adhesive is sensitive to hygrothermal exposure, which may lead to performance degradation of CFRP-steel bonded interfaces. In this study, the performance evolution of epoxy adhesives and CFRP-steel epoxy-bonded joints after hygrothermal exposure was investigated. Three hygrothermal exposure temperatures (25 °C/50 °C/75 °C) and three hygrothermal exposure times (24 h/120 h/360 h) were considered. The dynamic mechanical behavior and tensile properties of the bulk adhesives were studied by dynamic mechanical analysis (DMA) and tensile tests, respectively. Additionally, the mechanical failure properties of the bonded joints, including failure mode, strain distribution, and bond-slip relationship were obtained by tensile tests. The results indicated that the glass transition temperature (GTT) and tensile strength of adhesive J133 are always higher than those of A2014 in all test scenarios. The interface remains the weakest after hygrothermal exposure. After the 50 °C hygrothermal exposure, both CFRP-steel joints possess the highest bond strength and interfacial maximum bond stress, which corresponds to their higher adhesive tensile strength at the same temperature. In addition, we also find that both CFRP-steel joints show an increase in bond strength after short-term hygrothermal exposure.