UCRfr—ultrasonic critical-angle refractometry for stress measurement

An ultrasonic refractometry technique for measuring the velocity of longitudinal, shear and Rayleigh waves is presented. The need of developing the technique is to improve the traditional measurement methods in measuring the state of stress in material by means of acoustoelasticity. The technique is based on measuring the transmission coefficient in proximity to the first and second critical angle of refraction and the angle for formation of Rayleigh waves. The transmission coefficient was measured in relation to the angle of incidence of an ultrasonic beam on a water–aluminium and steel–aluminium interface, and was compared to the theoretical values with good results, considering also the finite size of the beam. It is shown how the velocity of the longitudinal, shear and Rayleigh waves can be measured with great accuracy by measuring the amplitude of the refracted signal in relation to the angle of incidence, in proximity to the critical angles of refraction, and how this technique presents some advantages over the traditional technique for measuring ultrasonic velocity, based on the measurement of time-of-flight and on methods involving reflectometry.