MODELING OF AN ELASTOPLASTIC PROCESSES IN SOLIDS DUE TO ANNEALING AND FOLLOWING THERMOMECHANICAL

  • V. S. Mykhailyshyn Pidstryhach Institute for Applied Problems of Mechanics and Mathematics National Academy of Sciences of Ukraine
Keywords: annealing, temperature, stresses, strains, plastic deforming, thermosensitivity, hardening, finite element method

Abstract

This work is oriented on the sequential solving of two problems: 1) the estimation of the relaxed stresses in metallic products on cooling stage in its high-temperature annealing process; 2) the estimation of the stresses in these products with obtained distribution of stresses relaxed consequently to annealing, where the products are subjected to thermomechanical influences modeling the working conditions after annealing. Common character and particularity of both problems is presence of residual (initial) stresses. It is validated an importance of investigation concerning initial stress redistribution in cooling condition during annealing and condition modeling working conditions of annealed products. It is proposed the approach to study of thermomechanical processes in products during cooling in high-temperature annealing and following after annealing thermomechanical influences realized during exploitation of products and constructional elements with known initial previously acquired stresses. This approach consists in stage-by-stage formulating and solving using the finite element method (FEM) of problems about thermal and mechanical states with various initial and boundary conditions for every stage. These stages are: 1) the estimation of the stresses relaxed at the end of annealing; 2) the stress estimation in solids loaded after annealing. Within nonstationary heat conductivity theory and plastic nonisothermal yielding theory the thermomechanics problem has been formulated. It is assumed a quasi-static deformation processes. The isotropic materials are considered. The solids are cooled by heat exchange with environment. The criterion of plastic deformation is von Mises condition modified on the isotropic-kinematic hardening case. It is assumed a thermal sensitivity of material properties in the considered temperature spans and hardening possibility in plastic deformation. The developed software is adapted to solving of defined kind of two-dimensional problems for solids with initial stresses. A process of solution obtaining on the ground of developed FEM program system has been schematic illustrated.

As example the stress state is investigated in the thin circular disc of steel with concentric coaxial hole and heat-insulated front-face surfaces. The regularities concerning character and level of stresses in solids under simulated working conditions are established depending on model approaches of hardening material properties. The calculating aspects of problems solving are discussed including discretization of geometrical domain and step-by-step discretization. For comparison the results are realized concerning of common influence of pressure and thermal field on stress state in disc without initial stresses for elastic-plastic isotropic-kinematic hardenable material and assuming elastic behavior of material. According to the results of computer simulation experiment the stress distribution in disc with residual stresses, typical in weldments, is obtained in cooling conditions during annealing also in conditions of common influence of static mechanical loading and nonstationary thermal field after annealing. In this connection the estimation of stresses initial before cooling is validated. This estimation is based on known before annealing stress distribution and known experimental observations and theoretical facts. The results are obtained assuming an ideal plastic deformable material and for three hardening models. The isotropic, kinematic and isotropic-kinematic hardening cases have been considered. The results are presented according to step-by-step change of applied pressure and temperature. The regularities concerning character and level of stresses in solids under simulated working conditions are established depending on model approaches of hardening material properties. These regularities consist in appreciable influence of welding stresses, relaxed after annealing, on mechanical behavior in neighborhood of welded seam. The lesser significant distinctions in kind and appreciable quantitative distinctions in stress distribution depending on model approaches of material hardening properties have been observed (ideal material, kinematic hardening, isotropic-kinematic and isotropic hardening).

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Published
2020-03-03
How to Cite
Mykhailyshyn, V. S. (2020). MODELING OF AN ELASTOPLASTIC PROCESSES IN SOLIDS DUE TO ANNEALING AND FOLLOWING THERMOMECHANICAL. Bulletin of Zaporizhzhia National University. Physical and Mathematical Sciences, (2), 101-116. Retrieved from http://journalsofznu.zp.ua/index.php/phys-math/article/view/260