Tensile fatigue properties of composite/metal bolted joints with 3-pin and sleeves

Countersunk bolt joints with sleeves have been used in composite connection structures, and the fatigue properties need to be studied. In this study,a static tensile test is carried out on a single lap CFRP/titanium alloy bolted joint with 3-countersunk head bolt and sleeves, and the load-displacement curves, ultimate tensile strength and off-set bearing strength of the joint are measured. On this basis, 67% of the joints ultimate load is determined as the maximum tensile fatigue load. The joint is tested with a stress ratio of 0.1 and compared with the joint without sleeves to investigate the sleeves influence on the joints fatigue performance. The results show that the use of the sleeves improves the stress distribution and increases the fatigue life of the structure by 98.4%. At the same time, hole bearing and net section tensile failure of the laminate occurred in the static tensile test. In the fatigue test, tensile fatigue failure of the titanium alloy plate occurred, and bolt fatigue fracture also occurred in some joints without sleeves. It is found that the fatigue failure mode of the composite/metal mechanical joint varies with the load level due to the large differences in the fatigue performance of the two types of materials, and the metal structure is prone to damage when the load is lower a certain level.