Efficient crystal plasticity simulations of microstructure evolution

Sammanfattning: One of the common tools for studying the deformation behavior of the microstructure in polycrystalline materials is crystal plasticity models. These are used to describe texture evolution and hardening due to crystallographic slip. A drawback when using crystal plasticity models is that the calculation of the slip requires solving a set of stiff differential equations for each grain in the microstructure, yielding a high computational cost. In order to reduce this cost, the program has in the present work been ported to a graphical processing unit (GPU), to utilize the capabilities for parallel performance available on the GPU. Different strategies for the numerical implementation of crystal plasticity are investigated as well as a number of approaches to parallelization of the program execution. Crystal plasticity models based on the Taylor assumption are well suited for describing the plastic deformation of polycrystal grain structures, but are not equipped to model recrystallization since the topology of the grain structure is not defined, and there is no description of inter-connectivity between grains. Therefore the crystal plasticity model is combined with a graph-based vertex algorithm in this work. This formulation is capable of capturing finite-strain deformations, development of texture and microstructure evolution through recrystallization. The polycrystal plasticity model is employed in a finite element setting and allows tracing of stored energy build-up in the microstructure and concurrent reorientation of the crystal lattices in the grains. This influences the progression of recrystallization as nucleation occurs at sites with sufficiently high stored energy gradients and since the grain boundary mobility and energy is allowed to vary with crystallographic misorientation across the boundaries. The proposed graph-based vertex model describes the topological changes to the grain microstructure and keeps track of the grain inter-connectivity. Through homogenization, the macroscopic material response is also obtained. By the proposed modeling approach, grain structure evolution at large deformations as well as texture development are captured.