Acoustic nonlinearity of cracks partially filled with liquid: cubic approximation.

The theoretical investigation of mechanisms of the acoustic nonlinearity (elastic and inelastic) of cracks partially filled with an ideal and viscous liquid and associated with the nonlinear dependence of the capillary and viscous pressure in the liquid on the distance between the crack surfaces and the velocity of the change of this distance is proposed. The nonlinear (in cubic approximation) equations of the state of these cracks is obtained, and its parameters are defined. It is shown that the presence of the viscous liquid may lead to the considerable increase of the acoustic nonlinearity of such cracks in comparison with cracks filled with the ideal liquid.