Dynamic interactions between two axially aligned threaded joints undergoing loosening

Abstract

Maintaining effective preload in bolted joints is critical for ensuring long-term performance and safety throughout the operation of any assembled structure, vehicle, or machine. The loosening of bolted joints has been studied since the Industrial Revolution, but modeling approaches have only emerged over the past three decades. Although existing approaches are capable of simulating or predicting loosening in a single joint consisting of a single bolt, they are too computationally expensive to be used to model loosening in large built-up structures consisting of dozens to thousands of joints. Recently, a new reduced-order modeling approach has been proposed for the reproducing the behavior of axially aligned threaded joints undergoing loosening due to shock excitation. The objective of this research is to apply this new approach to investigate how multiple joints can interact with each other through the global dynamics of the structure during loosening. Specifically, the new approach is applied to model the behavior of three rods connected together using two axially aligned threaded joints. The results demonstrate that the behavior of the three-rod system can be divided into five regimes based on applied loading: first, a low-amplitude (low-energy) regime where the evolution of each joint is independent of the other; second, a regime where the joints exhibit weak dependence on each other; third, a regime of strong dependence; fourth, a regime where bands of mitigation arise corresponding to only one joint loosening; and fifth, a regime corresponding to complete rapid loosening of the first joint. The third and fourth regimes reveal that when the joints are torqued to the same initial preload, regardless of the actual value, both joints will always loosen completely. However, when the joints are tightened to different amounts, there exist combinations where only one joint loosens completely, such that the other joint maintains some of the initial preload.