Monitoring method of bolt looseness based on inversion of joint surface gap by magnetic field change

Abstract

In the field of engineering, bolted connection structures are widely used, and loose bolts can lead to serious safety incidents. However, current monitoring techniques for bolt loosening are limited in their ability to detect the degree of looseness in real-time. To address this problem, this study proposes a novel approach to monitoring bolt loosening by using the inversion of magnetic field change combined with surface clearance. Firstly, the static magnetic field equation is theoretically derived using the Maxwell equation under the assumption of no current, and the sensitivity of the magnetic field to the gap is examined using finite element simulation. Secondly, a three-dimensional finite element model is established to conduct a parametric scan of the gap, and the relationship between the gap and magnetic field intensity is obtained. Furthermore, the study proposes a high-precision gap sensor design scheme, which is theoretically confirmed to be viable. To confirm the feasibility of the proposed bolt looseness monitoring method and the instrument development, a bolt looseness testing platform is built and applied in engineering practice. The research shows that this technique can successfully track the state of loosening bolts, offering a new approach and concept for bolt loosening monitoring. It has the potential for a wide range of applications.