Ultrasonic measurement method of stress based on longitudinal critical refraction wave considering the influence of coupling layer thickness

In this study, an ultrasonic longitudinal critical refraction wave (LCR wave) stress measurement method has been proposed, which takes into account the impact of coupling layer thickness on the acoustic time difference of ultrasonic wave propagation (Acoustic Time Difference, ATD) and quantifies the effects of coupling layer thickness and stress on ATD. The research initially systematically analyses the effects of coupling layer thickness and stress on the ATD, establishing a relationship model between the ATD and the coupling layer thickness and stress. Subsequently, data processing techniques are employed to isolate the ATD caused solely by stress from the data influenced by coupling layer thickness and stress, eliminating the coupling layer thickness's impact and thereby obtaining the ATD data free from coupling layer effects (S-ATD*). Finally, a relationship between the ATD and stress is established through fitting analysis, and precise stress measurement is achieved by incorporating the ATD data free from coupling layer effects. The relative error between the stress values measured by this method and the actual stress values is below 3%, validating its high precision and reliability. This method provides new theoretical references and application perspectives for ultrasonic stress measurement technology, and it holds significant engineering value for enhancing the safety of critical structures.