STUDY ON DISPERSION BEHAVIOR AND BAND GAP IN GRANULAR MATERIALS BASED ON A MICROMORPHIC MODEL

The design of metamaterials is paid more attention to control the behaviors of the wave propagation based on response characteristics of shock and wave in granular materials, and it requires in-depth understanding of the propagation mechanism and control mechanism of waves for granular materials. The dispersion behavior and frequency band gap of granular materials are closely related to the heterogeneity. Generally, the dispersion behavior and frequency band gap are based on the elastic theory framework to establish a generalized continuum model including the microstructural continuum or the high order gradient continuum. This study proposes a micromorphic continuum model based on micromechanics for granular materials. In this model, the translation and the rotation of particles are taken into consideration, and the relative motion between particles is decomposed into two parts: the macroscopic mean motion and the microscopic actual motion. Based on this decomposition, a complete pattern of deformation is obtained. The macroscopic deformation energy is defined by a summation of the microscopic deformation energy at each contact. As a result, the micromorphic constitutive relation can be derived, and the corresponding constitutive modulus can be derived by microscopic parameters in terms of contact stiffness parameters and microscopic geometric parameters. The proposed model investigates the propagation of waves in an elastic granular medium, give dispersion curves for different waves such as longitudinal, transverse and rotational waves and predict the frequency band gap. It proves that the proposed model has the ability to describe dispersion behaviors and predict the frequency band gap in granular materials.