Static component of nonlinear guided wave as a preferable indicator of creep damage in superalloys

Nonlinear ultrasonic testing based on second harmonic generation has shown promise for early-stage creep damage detection. However, its practical application is constrained by a strong dependence on mode-matching conditions and signal degradation at advanced damage stages, limiting its effectiveness in complex service environments. Additionally, traditional approaches struggle to reliably characterize microstructural evolution throughout the entire creep process, affecting the accuracy of damage evaluation. To overcome these challenges, this study introduces the static component signal (β₀) of guided wave propagation into the creep damage assessment of superalloys. This approach broadens the characterization scope of nonlinear ultrasonic responses and enhances detection stability during later creep stages. Experimental results demonstrate that the static component is largely insensitive to mode-matching conditions, with its nonlinear parameter exhibiting a stable, linear increase throughout the creep lifetime. Compared to the second harmonic parameter-which typically exhibits a nonlinear "rise-then-fall" trend-the static component shows improved robustness and practical applicability. This method effectively addresses the limitations of conventional nonlinear ultrasonic techniques for late-stage creep damage detection, offering a valuable complementary tool for structural health monitoring and life assessment of high-temperature materials.