Nonlinear ultrasonic detection of axial stress of fan bolts based on pulse inversion technique

To accurately measure the axial stress of fan bolts, this study proposes analysing the nonlinear ultrasonic properties using pulse inversion technique. The research explores the fundamental relationship between axial stress and the relative nonlinear coefficient. Key findings show that as the axial stress of the bolt increases from 0 MPa to 1000 MPa, the relative nonlinear coefficient increases monotonically, with the slope of the curve continuously rising. SEM analysis of the bolt tensile process reveals that changes in material microstructure are the primary cause of the relative nonlinear coefficient’s variation. Theoretical and experimental research further demonstrate that the pulse conversion method significantly improves the accuracy and effectiveness of axial stress detection in bolts. The major contributions include developing a detection system that leverages pulse-inversion technology to enhance the accuracy of axial stress assessment in wind turbine bolts. Our research reveals significant potential for ultrasonic nonlinear technology in evaluating operational wind turbine bolts’ axial stress, offering a non-destructive and efficient alternative to existing methods. This approach not only improves detection efficiency but also provides deeper insights into the material’s microstructural response to stress.