Influence of thermomechanical properties of epoxy resin on interface of CFRP/steel under high temperature

Given that CFRP and steel structures that are adhered to epoxy resins usually require high temperatures, the influence of the epoxy resins' thermomechanical properties on the interface behavior of CFRP/steel lap was addressed. The researchers chose epoxy adhesives with different glass transition temperatures to test at 25°, 55°, 70°, and 90°. The self-developed HJY-4105 high-tenacity epoxy resin structural adhesive (HJY) was compared with two commercial adhesives using static tensile tests on double-lap joints. The structural behaviors in load-carrying capacity, load-displacement relationship, and strain distribution at the interface were obtained. The effect of temperature on the interfacial stress transfer mechanism and bond-slip modeling was also investigated. The self-developed HJY adhesive showed the best mechanical properties at high temperatures, and the loading capacity of test specimens using HJY adhesive increased with temperature. The test specimens using Sikadur-30CN Adhesive (SIKA30) had the highest loading capacity at 55°C. The loading capability of specimens using LICA-100 A/B Adhesive (LICA) decreases with increasing temperature. As the temperature approached the glass transition temperature ( T g ) of the adhesive, the shear strength, peak interfacial shear stress, and shear stiffness of the adhesive decreased while the ductility increased. Furthermore, the strain distribution was modeled more accurately using third-order polynomials, and the fit-based strain analytical results provided strong support for a more in-depth study of the mechanical properties of the interface.