Load-equivalent model and loosening life prediction method of bolts under transverse loading

Abstract

To establish a method for predicting the loosening life of bolts under random transverse vibration, this study first obtains the transverse displacement–loosening life (D–NL) curves of bolts under three loosening states (90 %, 80 %, and 70 % of the residual preload) through bolt-loosening tests under different transverse displacement loads. Based on the mechanical analysis model of bolt loosening with strict physical definitions, load-equivalent models of the bolt external load, screw load, and screw-tooth root stress are established by considering the transverse displacement load as the input excitation and the screw-tooth root stress as the output response; these achieve the transfer and conversion of the bolt external load and screw root stress with the screw load as the bridge. Subsequently, two types of finite element models of bolted connections are established and verification tests are performed. The equivalent relationships between the bolt external load, screw load, and screw-tooth root stress are simulated and tested, and the accuracies of the bolt-load equivalent models are verified. Finally, based on the bolt-load equivalent models, the D–NL curves for evaluating loosening using the directional macroscopic displacement load are converted to stress–loosening life (S–NL) curves to evaluate loosening using the undirected local stress. A calculation flow of the bolt-loosening life under random transverse vibrations is established, and a method of predicting bolt-loosening life based on the bolt-load equivalent relationship is developed. These findings provide a useful reference for optimizing bolted connection designs and preventing bolt loosening.