A dual-frequency ultrasonic technique for testing nonlinear elasticity of dry sandstone

We present an experimental study on nonlinear elastic wave propagation in rock using a dual-frequency acoustic method, known as the SURF technique. The results are compared with previous tests, performed on the same types of sandstone, in which the low-frequency acoustic pulse was simulated via a small amplitude oscillatory stress. A clear relation between both results indicates that with sufficiently high acoustic pressure the elastic properties of the rock can be manipulated in a similar manner as it is done by the low amplitude mechanical stress oscillations. Thus, the SURF technique seems to have a potential for characterizing the rock formations in terms of their nonlinear elasticity, directly under in-situ conditions.