Modeling of influence of planar defects on plasticity of powder materials by computational methods of micromechanics

P. Korobko

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Kyiv
Usp. materialozn. 2021, 3:77-85


Based on the energy concept of the critic stress state, a three-parameter model of plasticity of the Cam-Clay type was formulated. For this phenomenological model, the dependences of the determining parameters on the porosity and damage were found by the method of micromechanical averaging on the unit cell corresponding to the porous damaged material of powder origin. The plastic multi-responce (different yield strength in tension and compression) behavior of this material is found by micromechanical averaging on a 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 mesolevel. 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 representative cell corresponds to a powder origin material with “imperfect”, partially stratified, interparticle contacts. 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 the degree of delamination of interparticle contacts. 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. The advantage of this approach is precisely in focusing on powder origin materials and not generally on any damaged materials, which makes it possible to take into account the real structure of the damaged material using the methods of mechanics of microheterogeneous materials. According to the simulation results, in particular, it was found that the yield strength for shear is significantly (30%) less sensitive to damage than the yield strength for uniaxial tension.

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