Summary
The loosening of bolts negatively impacts many industries worldwide. This issue, for example, can be responsible for the collapse of a structure or vehicle, leading to environmental disasters, economic loss, injuries, and death. Current strategies for simulating loosening include high-fidelity finite element models or analytical expressions, based on assumptions of the motion across the join. In both cases, the feasibility of modeling multiple bolts undergoing loosening and their potential interactions with each other are compromised by computation costs and underlying assumptions. To tackle this problem, this research introduces a novel reduced-order modeling approach designed to depict the dynamics of loosening bolts in lap-jointed structures. The study centers on two harmonic oscillators joined by a lap-joint with a single tension-sensing bolt, which experiences loosening due to uniaxial transverse free and forced vibrations. The study is divided into three stages: in the initial stage, the inherent linear characteristics of each oscillator operating independently are identified and modeled; in the second stage, the connection between joint properties (specifically stiffness and damping) and bolt tension is established through lowamplitude modal impacts across various tension levels; and in the third stage, the system is subjected to high-amplitude forcing to induce loosening, and the resulting loss of tension is depicted through a first-order ordinary differential equation. As a result, the findings reveal that the identified model effectively reproduces the structure's measured reaction in response to the bolt's loosening
