MODELING OF MULTIMODULUS ELASTIC BEHAVIOR OF DAMAGED POWDER MATERIALS USING COMPUTATIONAL MICROMECHANICS

Abstract

The work aimed to improve the fundamental acoustic defectoscopy principles of green compacts and weakly sintered materials. A theoretical method for determining the elastic properties of powder porous materials with distributed microdefects has been proposed. The nonlinear elastic multi-modulus (different stiffness in tension and compression) behavior of this material has been described by micromechanical averaging on a representative cell. According to the mechanics of composites, the cell geometry represents the structure of a heterogeneous material, and the boundary conditions on a representative cell enable relating the stress-strain state at the macro- and meso-level. The averaging was carried out by computer simulation using the finite element method with an adaptive mesh, which automatically condensed in the places of the large gradient stress-strain.  The structure of the representative cell corresponds to a powder material with “imperfect”, i.e., partially stratified, interparticle contacts. In the proposed model, the rheological response of a porous damaged material is specified by three elastic moduli. The structure of such a material is described by two internal state parameters, namely, the porosity and the degree of interparticle contacts delamination.  That is, the elastic moduli are functions of porosity and damage.  Accordingly, several values of elastic moduli were calculated for a discrete density and damage range. The advantage of this approach is focusing precisely on the powder materials rather than on any damaged material, in general, which allows considering the real structure of the damaged material using the mechanics of microheterogeneous materials.  The developed structure-sensitive elasticity model enabled establishing the relationship between the defectiveness of a porous sample and the resonant frequency of its free vibrations.