Dr. Keegan J. Moore
Date of this Version
S. A. Aldana, Reduced-order Modeling of Loosening in Bolted Joints and Dynamic Interactions Between Axially Aligned Threaded Joints. MSc Thesis, Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln,2021.
Maintaining effective preload in bolted joints is critical for ensuring long-term performance and safety throughout the operation of any assembled structure. 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 structures consisting of many bolts. The objective of this thesis is to construct and employ a reduced-order modeling (ROM) approach that treats the internal tension or the torque applied to the joint as a degree-of-freedom (DOF) that evolves dynamically with the structure. In this thesis, the approach is applied to threaded joints coupling axial rods and the torque applied to each joint treated as the new DOF. The method is first applied to predict the loss of torque in a system consisting of two axial rods connected by a single threaded joint and the simulated results are compared to experimental measurements. The method is then used to investigate the dynamic interactions between two threaded joints coupling three axial rods together. The idea is that by understanding these interactions, they can be exploited to nullify loosening or even heal joints that have already loosened. The results demonstrate that the behavior of the three-rod system can be divided into five regimes based on loading: first, a low-amplitude regime where 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. However, when the joints are tightened to different amounts, there exist combinations where only one joint loosens, such that the other joint maintains some of the initial preload.
Advisor: Keegan J. Moore