Digital Image Correlation-Based Bolt Preload Monitoring

Bolt connections are widely used in engineering structures but are prone to loosening during service, which may lead to serious safety issues. Therefore, reliable bolt-loosening detection is of great importance. Traditional detection methods often suffer from drawbacks such as low efficiency, limited accuracy, and the need for contact sensors. To overcome these limitations, this study proposes a novel non-contact approach for bolt preload monitoring based on Digital Image Correlation (DIC). In this method, an industrial camera captures speckle images of the bolt head before and after deformation, enabling measurement of the surface strain. The DIC technique is employed to calculate the strain field on the bolt head surface, which exhibits a linear relationship with the bolt preload. By tracking changes in this strain field, the proposed method allows effective and accurate monitoring of bolt preload. Experimental results demonstrate that the method provides a precise, efficient, and user-friendly solution for bolt preload monitoring, showing great potential for applications in structural health monitoring.