Tensile tests and strength estimation for double-lap single-bolt joints in T800 carbon fiber reinforced composites

In order to investigate the mechanical properties of bolted joints in T800 carbon fiber reinforced composites systematically, in-plane quasi-static tensile tests were carried out on double-lap single-bolt joints in T800 carbon fiber reinforced composites firstly, and the effects of ply ratio, ply sequence, bolt diameter and curing method on stiffness and 2% offset bearing strength of composite bolted joints were discussed. Then, based on test results, stress concentration relief factors for bolted joints in T800 carbon fiber reinforced composites were obtained. Finally, combining the stress concentration relief factor and tensile strength of un-notched laminates with the corresponding plies, an engineering approach for the ultimate bearing strength of composite bolted joints was established. The results show that when bolt fractures, the ultimate bearing strength of joints is decided by the shear strength of bolt and the bolt diameter/laminate thickness ratio. Joints have two collapse modes concluding bearing and shear, and they are related with the ±45° ply ratio. The calculated results of engineering approach agree well with the test results. The test results and engineering approach obtained can provide theoretical proofs and technological supports for the preliminary design of T800 carbon fiber reinforced composite bolted joints.