Degradation of an underwater epoxy adhesive and its bonding to steel subjected to water or seawater immersion

Abstract

Underwater adhesive is used to bond carbon fiber reinforced polymer (CFRP) composites to offshore or underwater structures. However, the long-term moisture exposure poses a challenge to the reliability and service life of the underwater adhesives. Therefore, the present article aims to provide a deep understanding of the durability of the underwater adhesive and the long-term bond performance between the CFRP and steel. The hygrothermal resistances of an underwater adhesive and CFRP-adhesive-steel double cantilever beam (DCB) immersed in deionized water and seawater at 25 °C, 40 °C, and 60 °C were investigated. The degradation mechanism was determined by the chemical characterization of the adhesive. Dynamic thermomechanical properties and tensile strength degraded significantly (≥62 %) before water uptake saturation due to adhesive plasticization. A high temperature (60 °C) can improve Mode I fracture toughness by at least 68 % due to an increase in the toughness of the adhesive.