Hysteretic nonlinear elasticity of Berea sandstone at low-vibrational strain revealed by dynamic acousto-elastic testing

Through changes in wave speed of ultrasonic pulses traversing the sample, we measure variations in the elasticity of dry Berea sandstone as a function of the applied low-frequency (LF) axial strain (varied from 10(-7) to 10(-5)). The approach, termed dynamic acousto-elasticity, is the dynamic analog of static acousto-elasticity where the wave speed is measured as a function of the applied static load. Dynamic acousto-elasticity uses low-frequency vibrational loading of smaller strain amplitude, typically below 10(-4), and it includes inertial effects. At strain amplitudes around 10(-6), compression and tension produce a material softening of the material. In contrast, a quasi-static compression inducing a strain between 10(-4) and 10(-3) leads to a material stiffening. At 10(-5) strain amplitude, elaborate hysteretic signatures of modulus strain are observed. The measurements provide the first direct experimental evidence of hysteretic nonlinear (wave amplitude dependent) elasticity in a sandstone at low dynamic strains. Citation: Renaud, G., J. Riviere, P.-Y. Le Bas, and P. A. Johnson (2013), Hysteretic nonlinear elasticity of Berea sandstone at low-vibrational strain revealed by dynamic acousto-elastic testing, Geophys. Res. Lett., 40, 715-719, doi:10.1002/grl.50150.