Mechanical properties of 3D six-directional braided composites single-lap bolted joints under tensile load

The properties of 3D six-directional braided composite bolted joint structure were investigated by the test and numerical simulation. First, the joint strength of bolted joint structure with different lateral restraint was tested by tensile test. The test results show that the second bend phenomenon of the single-lap joint structure is obvious, there is a certain relationship between joint strength and lateral restraint. The joint strength can be effectively improved by using the gasket. The increase of tightening torque of bolted has little effect on joint strength. The failure modes of joint structure include bearing failure and tensile failure. The dominant failure mode is bearing failure when the aperture is small. Then based on the failure mode which was found in test, the analytical model was established basing on the point stress criteria, and the tightening torque was applied to the bolted joints by using temperature rising method. The reliability analysis model can be verified by comparing the numerical results with the test results. Finally, the verified analytical model was used to analyze the second bend phenomenon of single-lap bolted joint structures. The effects of lateral restraint area, tightening torque of bolted joints and the plate thickness on mechanical properties of single-lap bolted joint structures were obtained. The results indicate the joint strength first increases and then decreases with the increase of lateral restraint stress.