Optimizing guided wave propagation for sensitive axial stress measurement in steel pipes

Steel pipe structures are commonly used in the industrial field. Stress-induced structural failures can have a significant impact on equipment safety. Therefore, effective stress monitoring is a crucial area of research. Constrained by the multi-frequency and multi-modal characteristics of ultrasonic guided waves, the limitations of traditional stress measurement methods based on these waves lie in the lack of a systematic analysis of the impact of multi-modal fused signals on stress measurement. To explore the optimal guided wave stress measurement strategy, a mathematical model for the propagation of longitudinal guided waves in prestressed steel pipes, based on the principles of acoustoelasticity, is proposed. Using this model, the sensitivity of stress to each sub-mode of the longitudinal guided waves is analyzed, leading to the identification of the optimal guided wave mode (L(0,2) mode) and frequency range. In order to avoid the excitation of other low-sensitivity modes, further analysis of the optimal parameters for the piezoelectric array is conducted. Simulation results indicate that the designed transducer can effectively excite the target mode with high purity. The stress sensitivity of the target mode was experimentally determined to be $-2.5\times 10^{-5}{\text{MPa}}^{-1}$, which closely aligns with the theoretical results. Comparative analysis of the experiments emphasizes the influence of modal control on measurement outcomes. By selecting and controlling the appropriate mode, the maximum relative error in stress measurement is observed to be 5%.