# Digital Image Correlation-Based Bolt Preload Monitoring

## TL;DR

This paper introduces a non-contact method using digital image correlation to monitor bolt preload, offering a more efficient and accurate solution for detecting bolt loosening in engineering structures.

## Contribution

The novel non-contact bolt preload monitoring method using Digital Image Correlation (DIC) is introduced.

## Key findings

- DIC captures speckle images to measure surface strain on bolt heads.
- The strain field shows a linear relationship with bolt preload.
- Experimental results confirm the method's precision and efficiency.

## Abstract

Bolt connections are widely used in engineering structures but are susceptible to loosening during operation, which can result in significant safety concerns. Consequently, reliable bolt-loosening detection is of paramount importance. Conventional detection methodologies frequently exhibit deficiencies, including reduced efficiency, constrained accuracy, and the requirement 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, thereby 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. The proposed method utilizes strain field tracking to facilitate effective and precise 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.