Finite Element Modeling of Early Stage Self-loosening of Bolted Joints

Abstract

Bolted joints is one of the most widely used connections due to relatively simple structure, easy accessibility and reliability. However, Bolted Joints will gradually lose the clamping force under cyclic external loading, especially transverse loading. In order to fully reveal the nature of early stage self-loosening of bolted joints, in view of the common bolted joints of grade 6.8, this paper firstly establishes the elastic finite element model, and analyzes the change of clamping force under different pre displacement. The results show that the clamping force is proportional to the pre displacement. Then, in view of the common bolted joints of grade 6.8 under transverse cyclic loading, this paper establishes the elastic-plastic finite element model, and simulates the process of early stage self-loosening of bolted joints under different lateral cyclic load amplitude, different initial preload, and different clamping surface friction coefficient. It can be seen that the early stage self-loosening of bolted joints under lateral cyclic loading is due to the accumulation of local cyclic plastic deformation at the root of the engaged thread. The bigger lateral cyclic loading amplitude leads to the faster self-loosening. The greater preload will result in a greater remaining clamping force. There is almost no relationship between the friction coefficient of clamping surface and the self-loosening of bolted joints. Reasonable preload can effectively improve the bolted connection relaxation.