Ing. Milan Jarý, Ph.D. - thesis details

Name Ing. Milan Jarý, Ph.D.
Name of project Computer Simulation of Welding Processes and Thermal Treatment of Steel Using an Elastic-ViscoPlastic Material Model
Name of school Brno University of Technology
Faculty of Mechanical Engineering
Institute of Solid Mechanics, Mechatronics and Biomechanics
Beginning of studies2008
Completion of studies2013
Synopsis The purpose of this thesis is to correctly analyse and predict deformation-stress response (in the form of residual stresses) to technological processes taking place on polyform behaviour steel designed for practical application (energy industry, petrochemical industry, etc.). It means technological processes of welding and thermal treatment analysed by means of experiments and computer simulation. Computer simulation of welding and thermal treatment derives from the finite element method (FEM). Welding and thermal treatment always cause residual stresses in the weld joint and its neighbourhood. One of the requirements for weld joint quality of machine parts, especially parts in energy industry, is to maintain the required level of residual stress. And this issue, i.e. the correct and effective prediction of residual stresses in the weld joint, is the subject-matter of this dissertation. The courses and values of residual stresses may be important input parameters for subsequent evaluations. They may include, e.g. the evaluation of welded structure lifetime (fatigue, fracture deformation evaluation), optimization of holding time under thermal treatment or dealing with the problem of hot-cracking. Therefore it is important to run a credible computer simulation of the welding process and thermal treatment while giving a suitable and correct description of the physical processes taking place. To calculate residual stresses in the course and after welding, especially the following types of constitutive models of materials are currently used. The elastic-plastic model of material with isotropic reinforcement is the first of them, the elastic-plastic model of material with kinematic reinforcement is the other one and the combination of the above two models may be the third model. However, these materials models fail to consider significant viscoplastic, time-dependent deformation processes in the material taking place in the course of welding and thermal treatment. The failure to include these processes in the computer simulation may result in unrealistically high values and a different course of predicted residual stresses in the weld joint and its neighbourhood. Therefore it is necessary to take these physical processes into consideration by means of a suitable elastic-viscoplatic (EVP) model.

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