Nonlinear relaxation in geomaterials: New results

Numerous acoustic experiments demonstrate that in media with a complex structure, such as rock, the elastic response is characterized by (i) a decrease in the material modulus during wave excitation, typically with a hysteresis (fast nonlinear dynamics), and (ii) long-time recovery to the original equilibrium modulus (slow dynamics). Here, a physical model of a granular material with an inter-grain contact potential having one or more metastable wells suggested earlier is significantly developed to include a non-logarithmic stage and the joint action of excitation and recovery. Theoretical results are compared with our experimental data.