Influence of elevated temperatures on the bond performance of CFRP-steel lap joints bonded by nanosilica-modified adhesive with mixed curing agents

Elevated temperatures may influence greatly the mechanical properties of adhesives, and it is difficult for adhesives with a single curing agent to meet the requirements of adequate heat resistance and toughness simultaneously. First, this paper proposes a nano-SiO2-modified epoxy adhesive (GY34) using mixed curing agents to improve the bond performance of CFRP-steel joints at a high temperature. Then, studies are taken to examine the impact of elevated temperatures on the mechanical performance of GY34 with mixed curing agents and the interfacial properties of CFRP-steel double-lap joints bonded by GY34. After that, models are developed to predict the bearing capacity and bond-slip of CFRP-steel double-lap joints at different temperatures using the test data. The results indicate the toughness is optimal at 70 °C when the curing agents C105 and D230 are mixed with a mass ratio of 1:2. The bearing capacity of the CFRP-steel lap joint bonded with GY34 is much higher than the cases only bonded with a single C105 or D230, respectively. Moreover, the load-displacement curve has a significant ductile development stage as the temperature rises below the glass transition temperature (Tg, S), beyond which, the bearing capacity declines. In addition, the length of shear stress transmission and the effective bonding length increase significantly at high temperatures. The bond-slip curve bonded with GY34 has a trilinear trapezoid shape at different temperatures, and the peak shear stress and stiffness decline at various elevated temperatures. Finally, the relative slip and interfacial fracture energies increase first and then decrease with the rise of temperature.