FINDING BY COMPUTATIONAL METHODS OF MICROMECHANICS OF MULTI-RESPONCE RHEOLOGY OF SINTERING OF POWDER MATERIALS CONTAINING PLANAR DEFECTS

Abstract

The work is devoted to the improvement of the rheological theory of sintering of powder materials. A theoretical method for determining the viscous properties of porous materials of powder origin with distributed microdefects is proposed. The nonlinear-viscous multi-responce  (different tensile and compressive stiffness) behavior of such material is found by micromechanical averaging on the unit cell. According to the mechanics of composites, the geometry of the cell represents the structure of a heterogeneous material and the boundary conditions on a unit cell make it possible to relate 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 was automatically condensed in places of a large gradient of the stress-strain state. The structure of the unit cell corresponds to the powder material with planar defects that significantly exceed the particle size of the powder.. In the proposed model the rheological response of a porous damaged material is specified by three moduli, and the structure of such a material is described by two internal state parameters: porosity and defect concentration. That is, the rheological moduli are functions of porosity and damage.  Accordingly, a number of values of each of the moduli were calculated for a certain discrete range of density and damage. It was found that the degree of  the material softening due to planar defects significantly depends not only on the sign of the load, but also on the deformation scheme.