Stress Evaluation Using Ultrasonic Interference Spectrum of Leaky Lamb Waves

This paper presents a nondestructive stress evaluation technique using the ultrasonic interference spectrum of leaky Lamb waves. By using a specific pitch-catch ultrasonic setup, the symmetric and antisymmetric modes of Lamb waves in a finite plate are decoupled, leading to simple relationships between the modal frequency spacing of two adjacent modes in the interference spectrum and the acoustic wave velocities that are functions of stress. As a result, the stress in the plate can be determined by measuring the modal frequency spacing instead of the relative flight times to calculate the acoustic wave velocity. Extensive experiments were carried out to verify the viability and robustness of the new technique using a simple testing system. It has been demonstrated that the new technique is about 25 times more accurate than existing flight-time approaches using the same testing system. The experimental results agree well with the results obtained by other ultrasonic methods using expensive equipment.