Finite element analysis of bolted joints under torsional loads

The presence of service torque, which is generated after tightening, directly affects the mechanical properties of bolted joint. In this work, the mechanical behavior of bolted joints under torsional loads is investigated using finite element analysis (FEA). Models with two plates and multiple plates are established separately to investigate the mechanical properties of different kinds of bolted joints. Three analysis steps involving the entire process from tightening to torsional loading are adopted, namely tightening step, initial loss step and loading step. Torsional loads in two directions along the thread axis are considered and defined as loosening torsional load and tightening torsional load. The clamping force, as well as the friction torques of various contact surfaces, of the bolted joint are extracted in all the analysis steps. Different scenarios of friction torque combinations for bolted joints are obtained by means of adjusting the friction coefficient of the corresponding contact surfaces. On this basis, the mechanical properties of bolted joints and the corresponding torque thresholds are extracted on various scenarios. FEA results showed that how the service torque makes the directional characteristic of the mechanical properties of bolted joints under torsional loads. Moreover, the service reliability of bolted joint can be further improved based on the directional characteristics and the extracted torque thresholds.