Equation of state and wave propagation in hysteretic nonlinear elastic materials

K. R. McCall and R. A. Guyera
Earth and Environmental Sciences Division,
Los Alamos National Laboratory, Los Alamos, NM 87545

[a] Also at Department of Physics and Astronomy, University of Massachusetts, Amherst.


Abstract

Heterogeneous materials, such as rock, have extreme nonlinear elastic behavior (the coefficient characterizing cubic anharmonicity is orders of magnitude greater than that of intact materials) and striking hysteretic behavior (the stress-strain equation of state has discrete memory). A model of these materials, taking their macroscopic elastic properties to result from many mesoscopic hysteretic elastic units, is developed. The Priesach-Mayergoyz description of hysteretic systems and effective medium theory are combined to find the quasistatic stress-strain equation of state, the quasistatic modulus-stress relationship and the dynamic modulus-stress relationship. Hysteresis with discrete memory is inherent in all three relationships. The dynamic modulus-stress relationship is characterized and used as input to the equation of motion for nonlinear elastic wave propagation. This equation of motion is examined for one-dimensional propagation using a Green function method. The out-of-phase component of the dynamic modulus is found to be responsible for the generation of odd harmonics and to determine the amplitude of the nonlinear attenuation.