Tensile behavior analysis of CFRP (carbon-fiber-reinforced-polymer)-titanium joint under preload

Compared with the traditional connection (bonding and bolting), the hybrid connection has attracted increasing attention in various fields for its better mechanical properties. Some research demonstrates that providing preload, a necessary condition for bolted connection increases the strength of the conventional bolted joint. However, those research depends on the test procedure, and there are few studies on the mixed joint. In this paper, we studied the tensile behavior of CFRP(carbon-fiber-reinforced-polymer)/titanium alloy multi-bolt hybrid bonded/bolted (HBB) joints under preload with multiple parameters, such as the size of preload, the number of bolts, and the way of connection. A finite element model of joint strength prediction under preload based on the 3D Hashin failure criterion was established and combined with experimental verification. This work reveals that: The preload can effectively reduce the stress concentration around the bolt hole of CFRP laminate and enhance the strength of the mechanically fastened joints. As for the HBB joint, the simulation results of the scalar stiffness degradation (SDEG) of the adhesive layer indicate that the application of preload can also effectively slow down the failure process of the joint and has a significant impact on the strength of the joint. However, for the single-bearing full-thread bolted joint, the sizeable preloading force will lead to the extrusion deformation of the bolt thread and screw, and excessive preloading may even lead to the shear failure of the bolt.

Automated summary

Compared to traditional bonding and bolting, the hybrid connection has gained attention for its superior mechanical properties. This study investigates the effect of preload on the tensile behavior of CFRP/titanium alloy hybrid joints. It is found that preload can effectively reduce stress concentration and enhance the strength of mechanically fastened joints. However, excessive preload may lead to deformations or even failure in certain types of bolted joints.