Research on factors affecting competitive failure between loosening and fatigue of bolt under combined excitation

Abstract

At present, research on loosening and fatigue of bolt is relatively mature. But insufficient research on the competitive failure between loosening and fatigue of bolt under combined excitation, as well as its influencing factors still exits. Therefore, the competitive failure between loosening and fatigue of bolts was confirmed by conducting a competitive failure test under combined excitation and its influencing factors were analyzed based on this test. The analysis results show that the displacement-load ratio, load amplitude, phase difference and preload have a significant influence on the competitive failure between loosening and fatigue. The failure type of bolts is only related to the ratio of transverse displacement amplitude and maximum axial load (R). Meanwhile, there is a critical value of R that can determine that the bolt will occur loosening failure or fatigue failure. In this case, life of the bolts is mainly affected by the load amplitude, phase difference, and preload. The combined excitation amplitude and transverse load amplitude can accelerate bolt failure, while the axial load has different effects depending on its size. Finally, based on the analysis results, guidance and suggestions are provided for reasonably selecting various influencing parameters. According to the competitive failure relationship between the loosening and fatigue and the influence law of its parameters, it is convenient to predict the failure type and failure life of bolts under combined excitation, which provides a reference for engineering applications.