The Acoustoelastic Effect: EMAT Excitation and Reception of Lamb Waves in Pre-Stressed Metal Sheets

The acoustoelastic effect relates the change in the speed of an acoustic wave travelling in a solid, to the pre-stress of the propagation medium. In this work the possibility of assessing nondestructively the stress status in metal sheets, by using the acoustoelastic effect, is investigated. As the effect turns out to be very small for practical values of applied stress, the proposed technique relies on the use of a kind of non-contact ultrasonic transducers called EMATs (Electro-Magnetic Acoustic Transducer) for precisely measuring its influence on Lamb waves.