Mikromehaničko modeliranje oštećenja u sinteriranom čeliku

Today, the use of sintered steel materials in modern structures and power transmission systems is more and more frequent, and also inevitable. However, the microstructure of sintered steel is extremely porous, which leads to the phenomena such as stress concentrations, strain localizations and damage accumulations in the material microstructure. For this reason, to reliably assess the material behavior at the macro scale, it is necessary to model materials at the micro scale. In this thesis, by using the obtained results of the metallographic analysis, the micromechanical modelling of damage in sintered steel Astaloy Mo+0,2C of density 6,5 g/cm^3 was performed. In the microstructure modelling, the representative volume element (RVE) is used. The finite element method software Abaqus is used for numerical analyses. By using the existing constitutive damage and elastoplastic material models, the method for determining material characteristics of the sintered steel’s metal matrix was performed. The thesis is divided into seven chapters. In the first chapter, a brief introduction and description of powder metallurgy and sintering process is given, along with the basic properties of sintered steels. The second chapter presents the theoretical background of the constitutive material models for elastoplasticity and damage used in the numerical analyses. The third chapter deals with a detailed analysis of the numerical model based on the finite element method with a presentation of used finite elements. The fourth chapter describes the multiscale modelling used in the study of the heterogeneous material microstructure and explains the concept of RVE. In the fifth chapter, numerical microstructural analyses of selected RVEs were performed to determine the minimum size of RVE which will be used in the multiscale analysis. In the sixth chapter, the multiscale analysis of the tensile test was performed. The elastic region, elastoplastic region and elastoplastic region with damage were analyzed individually and the method for determining material characteristics of the metal matrix of sintered steel Astaloy Mo+0,2C of density 6,5 g/cm^3 was performed by modelling at the macro and micro scale. In the final, seventh chapter, the conclusion of the whole thesis is given.