A Low-Power Ultrasonic Residual Stress Measurement Method Based on the CM-SSA-VMD Denoising Algorithm

Welded structures are widely used in ships and marine equipment. The ultrasonic longitudinal critically refracted (LCR) wave method is a reliable technique for measuring residual stress in welded structures. Conventional ultrasonic measurement systems have high power consumption and are difficult to operate under the limited power supply conditions of marine environments. Reducing the excitation voltage can lower power consumption, but as the excitation voltage decreases, ultrasonic echo energy weakens and noise interference increases, thereby affecting the accuracy of stress measurement. This paper proposes a complexity-mutation-based adaptive singular spectrum analysis–variational mode decomposition algorithm (CM-SSA-VMD). The algorithm constructs a complexity index using the spectral centroid, waveform roughness, and zero-crossing rate. By identifying abrupt changes in complexity between adjacent singular spectrum analysis (SSA) components, it adaptively determines which components to retain for reconstruction. Then, variational mode decomposition (VMD) is used to further separate the residual high-frequency noise. Finally, the ultrasonic time of flight (TOF) is estimated using the cross-correlation algorithm, and the stress is calculated. The stress measurement accuracy of the proposed algorithm was evaluated at different excitation voltages: 5.2 V, 3.3 V, 1.2 V, and 0.5 V. The results show that when the excitation voltage drops to 0.5 V, after being processed by CM-SSA-VMD, the average relative error of stress measurement remains below 10%, while the average relative errors of a new adaptive denoising method, Grey Wolf Optimization–Variational Mode Decomposition–Wavelet Transform (GWO-VMD-WT), traditional FIR filtering and VMD are approximately 14%, 18% and 16% respectively. Compared with GWO-VMD-WT, FIR filtering and VMD, the measurement accuracy of this method is improved by 33.35%, 46.16% and 41.82% respectively. The CM-SSA-VMD algorithm can effectively suppress noise in ultrasonic signals at low excitation voltages and improve the reliability of stress monitoring. It provides a feasible method for low-power ultrasonic residual stress monitoring in marine engineering.