Competitive Failure of Loosening and Fatigue of Bolts under Composite Excitation

Abstract

At present, research on the loosening of bolts under transverse excitation and their fatigue under axial excitation has been relatively mature, but research on the competitive relationship and failure characteristics between loosening and fatigue of bolts under transverse and axial composite excitation is still insufficient. Therefore, a method to accurately determine the failure types of bolts is proposed in this study by conducting a competitive failure test of loosening and fatigue under composite excitation. According to this method, the failure types of bolts can be distinguished. The analysis results reveal that there is an obvious competitive failure relationship between the loosening and fatigue of bolts, and the failure mode is mainly affected by the ratio of the transverse and axial loads (ξ). There is a critical ξ of bolt-loosening or fatigue failure, and the critical ξ is an inherent property of the bolt and is unrelated to the load. The critical ξ of 8.8 grade M8 × 1.25 × 70 high-strength bolts under composite excitation is obtained as 0.075 mm/kN. The failure mode of bolts under composite excitation can be predicted based on the critical ξ.

Stiffness and geometry characteristics of flange connection with bolt failure and its influence on rotor dynamics

“…6 Yang et al 7 studied the competitive failure characteristics of bolt loosening and fatigue, and obtained the clamping force recession, load-life prediction, and critical-value prediction curves of the axial load to restrain bolt failure under combined loading. Yang et al 8 analyzed the competitive failure relationship between bolt loosening and fatigue under combined excitation through the competitive failure test of bolt loosening and fatigue under different preloads. Yang et al 9 established various discriminant models to classify the failure forms of bolts.…”