A new theoretical paradigm to describe hysteresis, discrete memory and nonlinear elastic wave propagation in rock

摘要

The velocity of sound in rock is astrong function of pressure, indicating that wave propagation in rocksis very nonlinear. The quasistatic elastic properties of rocks axe hysteretic, possessing discrete memory. In this papera new theory is developed, placing all of these properties (nonlinearity, hysteresis, and memory) on equal footing. The starting point of the new theory is closer to amicroscopic description of a rock than the starting point of the traditional five-constant theory of nonlinear elasticity. However, this starting point (the number density ρ of generic mechanical elements in an abstract space) is deliberately independent of a specific microscopic model. Noprejudice is imposed as to the mechanism causing nonlinear responsein the microscopic mechanical elements. The new theory (1)relates suitable stress-strain measurements to the number density ρ and (2) uses the number density ρ to findthe behaviour of nonlinear elastic waves. Thus the new theory providesfor the synthesis of the full spectrum of elastic behaviours ofa rock. Early development of the new theory is sketched in this contribution.