Effect of Bolt Looseness on Fracture Position and Fatigue Life of Bracket Arm for Air Spring Bellow

In view of two kinds of fatigue fracture of the bracket arm for air spring bellow of a heavy truck, fatigue tests were carried out, which comprehensively considering its actual assembly on the vehicle and load conditions. It was confirmed that the bolt looseness was the fundamental cause that affects the fracture position and fatigue life of the bracket arm. The finite element model of the bracket arm in bolt looseness-state and clamping-state was built. On which a static analysis was conducted under the ultimate static load condition, and then the stress distribution was obtained. Based on the Strain-life theory, the E-N curve of the material was obtained by fitting. As well as by the result of finite element analysis, the fatigue life analysis of the bracket arm based on the time domain was completed by nCode. Then the cloud diagram of the fatigue life distribution and the fatigue damage hot spots were obtained. And the correctness of the fatigue calculation results of the finite element model was verified by comparing with the fatigue test. The results show that not only the distribution of fatigue damage and the fatigue fracture position affected by the bolt looseness, but the fatigue life. When the bolt is loose, the fatigue life of the bracket arm decreases obviously. It provides a theoretical basis and the reference for the optimization design and the assembly of the bracket arm on vehicles, and offers a reference method of durability analysis for the bracket arm of air suspension systems.