Modeling Material Modifications Using a Process Independent Approach

Abstract

In forming industry, the generation of desired material properties in the surface layer is a challenging task. The results are highly dependent on the process parameters such as the tool geometry or the applied loading. As these parameters change from process to process, it is merely impossible to directly compare different processes as e.g. deep rolling, turning, or milling. Therefore, it is desirable to derive a process independent physical description that connects the loading state to the resulting properties. On the one hand, this necessitates the derivation of a universal material impact that describes the loading adequately (e.g. strain or temperature field). On the other hand, a general description of the material modification is needed (e.g. residual stresses or change in hardness). However, it is not straightforward to experimentally deduce the corresponding impact state from a process. Therefore, numerical investigations are used which include micro and macrostructural physical phenomena and help to deepen the understanding of the process. Indeed, the deduction of material loads such as the strain state or the temperature field is straight forward using the finite element method (FEM) as these quantities result directly as degrees-of-freedom (DOF) for every nodal point in the specimen domain. Furthermore, these quantities can be coupled to microstructural phenomena such as e.g. evolution of plasticity or phase transformations. In this research, a von Mises-type plasticity model is combined with a Hashin Shtrikman analytical homogenization procedure. Koistinen-Marburger model is incorporated to calculate austenitic and martensitic phase fractions inside the specimen. The model is evaluated through simulating the deep rolling process of a 42CrMo4 steel at isothermal temperature using the finite element (FE) software ABAQUS.