Bond behavior of hybrid FRP-to-steel joints

This paper presents experimental and numerical studies on the bond behavior of hybrid fiber-reinforced polymer (FRP)-to-steel single-lap joints. The hybrid FRP is comprised of inner and outer layers of glass FRP (GFRP) and one intermediate layer of carbon FRP (CFRP). For comparison, the bond behavior of CFRP-to-steel single-lap joints was also examined. Test results show that hybrid FRP-to-steel joints have similar failure modes with three-layered CFRP-to-steel joints. The bond strength of hybrid FRP-to-steel joints is much higher than that of one-layered CFRP-to-steel joints but slightly lower than that of three-layered CFRP-to-steel joints. The effective bond length of hybrid FRP-to-steel joints is close to that of three-layered CFRP-to-steel joints. The numerical investigation indicates that each layer of FRP in the hybrid FRP-to-steel joint undergoes more deformation than the corresponding layer of FRP in the three-layered CFRP-to-steel joint. It confirms that there is a hybrid effect between the inner and outer layers of GFRP and the intermediate layer of CFRP. This is the reason for the effective use of hybrid FRP. Finally, considering the hybrid effect, modified ultimate bond strength and effective bond length models for hybrid FRP-to-steel joints are proposed based on existing modes for CFRP-to-steel joints.