Mechanical-electrical-thermal multiphysics modelling and experimental validation of bulk-wave propagation in 316LN...

Ultrasonic bulk-wave propagation and detection under cryogenic conditions (77 K) pose significant challenges, as the effects of extremely low temperatures on acoustic coupling and wave behavior remain insufficiently understood. To address this issue, a novel mechanical-electrical-thermal coupling simulation approach is proposed to investigate the propagation characteristics of bulk waves in cryogenic environments. A temperature-dependent electromechanical model of the piezoelectric transducer (PZT) was established, in which the piezoelectric and dielectric properties were implemented as fitted nonlinear functions of temperature to capture the cryogenic response. In addition, a thermo-elastic stress-transfer model of the PZT-adhesive layer-structure system was developed to elucidate the coupling mechanisms induced by temperature-dependent physical properties such as damping and elastic modulus. Based on COMSOL finite element analysis, a fully coupled mechanical-electrical-thermal simulation model was constructed, and the acoustic properties of 316LN stainless steel were obtained within the temperature range of 293 K-77 K and validated through vacuum cryogenic experiments. The results show that at 77 K, the longitudinal-wave amplitude decreases by approximately 60%, while its velocity increases by 97 m/s compared with room temperature. The simulated and experimental data exhibit excellent agreement, with maximum relative deviations of 4.08% in amplitude and 0.34% in velocity, together with a consistently high envelope-based waveform correlation (0.949-0.969) over 77-293 K. The model-experiment agreement was further contextualized by an uncertainty estimate of the velocity measurement and a one-at-a-time sensitivity analysis, supporting the robustness of the proposed coupled model. These findings confirm the accuracy and reliability of the proposed model and demonstrate its potential for ultrasonic nondestructive evaluation of cryogenic components.