Ultrasonic surface wave technique to determine fatigue damage

The development of distributed microcracking gives rise to changes in the wave speed and the attenuation of ultrasonic signals. In this paper an experimental method is discussed which employs an ultrasonic bridge in conjunction with a self-calibrating technique, to accurately measure changes in velocity and attenuation of surface waves which propagate over a specimen of Al-Sic composite that has been subjected to fatigue loading. In a complementary theoretical approach, the scattering cross section of a single surface-breaking crack is employed as a measure of energy removal from the incident surface wave, and energy considerations are subsequently employed to obtain the coefficient of attenuation.