Coupling mechanism and critical effects of ultrasonic imaging for corrugated interface: a Rayleigh perturbation approach

The bonding integrity of corrugated interfaces in clad plates fundamentally governs their macroscopic performance, yet high-precision nondestructive evaluation (NDE) of these geometrically complex bonds remains a critical industrial challenge. Addressing the inspection demands for corrugated clad plates, this study investigates Cu/Al laminates as a representative system. A multi-parameter coupling framework integrating Rayleigh perturbation theory and critical slope criterion is established to enable quantitative prediction of imaging quality for corrugated interfaces. For the first time, the dimensionless parameter cp is proposed as a scale-invariant criterion to characterize imaging failure. Through systematic finite element simulations, the nonlinear coupling effects of corrugation wavelength, amplitude, and interface depth on imaging fidelity are quantified. The mechanism of imaging degradation at corrugation waists is elucidated via the relationship between local interface slope and ultrasonic reflection angle. Using Fermat’s principle, the minimum-time acoustic path in a bilayer medium is derived to analyze systematic imaging offsets caused by excitation-receiver separation. Experimental validation is performed on a laser-ultrasonic NDE platform using eight specimens with precisely controlled corrugation parameters fabricated by wire EDM. Results demonstrate excellent agreement with simulations, confirming the predictive accuracy of the theoretical model. The study reveals that when the maximum interface slope exceeds a critical threshold, reflected signals from waist regions fall outside the detection aperture, causing severe imaging quality deterioration. Decreasing wavelength, increasing amplitude, and increasing depth collectively exacerbate signal attenuation and geometric distortion. The proposed framework provides a theoretical foundation for quality assurance of corrugated clad plates and establishes a generalized analytical methodology for NDE of irregular multi-layered interfaces.