Improving torque-tension relationship in bolted joints: accurate threaded surface representation and pressure distribution considerations

The torque-tension relationship plays a vital role in the application of bolted joints, providing essential guidance not only in controlling the preload during the tightening process but also serving as the theoretical basis for measuring the coefficient of friction on threaded surfaces. In order to develop a better understanding of the torque-tension relationship, the force and torque on the contact surface during the preload process were analyzed using a differential geometric representation of the thread surface. This representation took into account three-dimensional effects of the thread surface, particularly its non-developability. The hexahedral meshed model of the bolted joints was used in the FEA of the tightening process to obtain the pressure distribution on the contact surfaces. Based on the accurate representation of thread surface and consideration of pressure distribution forms, a novel torque-tension relationship was proposed and compared with current relationships in the literature. The error analysis showed that the proposed formulation has lower relative errors with the FEA results than those in the literature, indicating a higher level of accuracy. This proposed torque-tension relationship not only improves the safety and reliability of bolted joints, but also contributes to a better understanding of thread mechanics during tightening process.