Experimental study of nonlinear elastic properties of unconsolidated medium under various external influences

In this work analysis of linear and nonlinear elastic properties of granular unconsolidated structure was carried out. The theoretical analysis based on the theory of nonlinear contact interaction described by Hertz. Equation of state for 3-D granular media was derived. Equations of elastic coefficients of the second, third and fourth orders, nonlinear parameters of the media and their dependencies on external pressure were obtained. We investigated experimentally the dependencies of the velocity of longitudinal waves on the external compression and amplitude of the input signal. The experimental results were in good agreement with theoretical predictions. An anomalous behavior of the nonlinear parameters of the medium when the external pressure applied to it was found. Authors suggested that this anomalous behavior was determined by the number of contacts between the balls and its character (strongly and weakly deformed contacts). This hypothesis was confirmed by measurements of electrical resistance of the system under consideration.