Multiscale modeling of dynamic recrystallization
Sammanfattning: During thermomechanical processing of metals, changes occur in the microstructure of the material which affect its macroscopic properties. By understanding these transformations in the microstructure, it becomes possible to design the processes in a way which yields the desired properties in the finished product. For this purpose, computer simulation plays an increasingly important role.The present work is focused on developing an efficient numerical model that captures the macroscopic material behavior as well as the microstructure evolution. The main part of the thesis is made up of four papers, A-D. In paper A, different numerical solution methods for crystal plasticity are compared and implemented to run on the Graphical Processing Unit (GPU). The use of GPUs for scientific computation allows for considerable parallelism to be achieved in an ordinary desktop, or even laptop, computer, and has also been proven to be a cheap and energy efficient alternative for use in clusters. Since polycrystal plasticity is well suited for parallelization, it is shown that considerable speedup, up to a factor of 100 in some cases, can be achieved.In paper B, the crystal plasticity model is coupled with a vertex model of grain structure evolution. This provides a versatile framework which can be used to model dynamic recrystallization at large deformations. The crystal plasticity model captures hardening and texture evolution during deformation, while the vertex model describes the recrystallization process in terms of nucleation and grain growth. This model is then applied to simulations of a hot rolling process in paper C, making itpossible to study how temperature, and thereby recrystallization, affects the texture evolution during rolling, and also to study the development of inhomogeneities in the microstructure throughout the workpiece. In the final paper, D, the model from paper B is further developed such that it can also account for the effects of grain size hardening and particle pinning of migrating grain boundaries.Taken together, the four papers A-D provide a numerical simulation framework with multiscale capabilities. By taking advantage of recent developments in computer hardware and using a combination of modeling approaches, a versatile tool is established. The model is capable of describing development of crystallographic texture and dynamic recrystallization, including effects of temperature and impurities in the material. Employed in a finite element setting, the effects of the microstructure evolution on the macroscopic properties of the metal are captured, providing a powerfulconstitutive model for thermomechanical processing.
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