Bolt Axial Stress Detection and Prediction Based on the Nonlinear Ultrasonic Technique

This study proposes a novel method for predicting the axial stress of bolts by analyzing their nonlinear ultrasonic characteristics. We first derive the theoretical relationship between the relative nonlinear coefficient and stress. Then, we build a detection system based on nonlinear ultrasonic technology to measure the axial stress of bolts. We find that the relative nonlinear coefficient of bolts increases with the stress, and the increase rate becomes faster when the stress exceeds a certain value. This indicates that the relative nonlinear coefficient is very sensitive to the stress change and can be used to accurately characterize the bolt axial stress. We normalize the relative nonlinear coefficient and fit the experimental data to create a bolt axial stress prediction model. We also use both nonlinear ultrasonic and linear ultrasonic methods to predict the bolt axial stress. The prediction results shows that when the axial stress exceeds 200 MPa, the prediction error of nonlinear ultrasonic is less than 5%, indicating that the prediction accuracy is significantly better than that of the linear ultrasonic method. In summary, this study demonstrates the effectiveness of nonlinear ultrasonic technology in detecting axial stress in bolts and offers a novel approach for the evaluation and prediction of bolt axial stress under service conditions.