Granular layers on vibrating plates: Effective bending stiffness and particle-size effects

Authors

Wonmo Kang, University of Nebraska - Lincoln
Joseph A. Turner, University of Nebraska - LincolnFollow
Florin Bobaru, University of Nebraska - LincolnFollow
Liyong Yang, University of Nebraska - LincolnFollow
Kitti Rattanidit, University of Nebraska - Lincoln

Date of this Version

February 2007

Comments

Published in J. Acoust. Soc. Am. 121 2
, February 2007. © 2007 Acoustical Society of America. Used by permission.

Abstract

Acoustic methods of land mine detection rely on the vibrations of the top plate of the mine in response to sound. For granular soil (e.g., sand), the particle size is expected to influence the mine response. This hypothesis is studied experimentally using a plate loaded with dry sand of various sizes from hundreds of microns to a few millimeters. For low values of sand mass, the plate resonance decreases with added mass and eventually reaches a minimum without particle size dependence. After the minimum, a frequency increase is observed with additional mass that includes a particle-size effect. Analytical nondissipative continuum models for granular media capture the observed particle-size dependence qualitatively but not quantitatively. In addition, a continuum-based finite element model (FEM) of a two-layer plate is used, with the sand layer replaced by an equivalent elastic layer for evaluation of the effective properties of the layer. Given a thickness of sand layer and corresponding experimental resonance, an inverse FEM problem is solved iteratively to give the effective Young’s modulus and bending stiffness that matches the experimental frequency. It is shown that a continuum elastic model must employ a thickness-dependent elastic modulus in order to match experimental values.