Modeling of material behavior in metal forming
Sammanfattning: With an increasing demand to improve efficiency and to cut costs, the industry is constantly seeking to reduce the time and money spent in product development and manufacturing. Use of computer-based simulations has become more or less a standard tool to meet this demand. Cost reduction is in this way made possible by for example shortened product development cycles, less need for expensive prototype testing, better material usage and optimized manufacturing processes. In order to obtain reliable simulations, a key ingredient is a sound description, or model, of the material behavior. Focusing on metal forming processes, the present work presents such constitutive models and simulation techniques that capture some important - but certainly not all - aspects of the material behavior during forming operations. Considering metallic materials, large deformations, phase transformation, rate dependence, recrystallization and coupled thermomechanical effects are treated. The thesis begins with a short introductory section that outlines some of the main topics discussed in the appended papers. The bulk of the thesis consists of five papers, A-E. Paper A describes the elasto-plastic behavior of steel at finite strains when diffusionless phase transformation is considered. Paper B focuses on coupled thermomechanical behavior in finite strain viscoplasticity, account thus being taken of both internal heating due to deformation and the effects of varying loading rates. Paper C proposes a model for material recovery due to dynamic recrystallization in finite strain viscoplasticity. Paper D is an extension and elaboration of Paper A, including full thermomechanical coupling. The effects of internal heat generation on the progression of martensitic phase transformation is studied. Paper E, finally, deals with the modeling of dynamic recrystallization on the microscale through the use of a cellular automaton technique.
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