Mechanics of grain interactions in polycrystalline metals


Metals are mostly used in polycrystalline form where the individual grains sizing from nm to mm interacts with their neighbours due to different orientations and elastic anisotropy of the crystal lattice . Consequently, the interactions lead to inhomogeneous strains and stresses within the grains. Strains and stresses must be then considered as distributions whose mean values over a sufficiently large neighbourhood (representative volume element]) correlate with the strains and stresses predicted by continuum mechanics ignoring the grain structure. Besides the elasticity, the grain interactions arise also from other deformation mechanisms on the crystal lattice level such as plasticity by dislocation slip and twinning, and martensitic transformation. Nowadays, experimental methods can probe the structure, and strains and stresses in individual grains of polycrystalline metals subjected to loadings. Furthermore, the geometry of internal grain structure of polycrystals can created using tessellation algorithms. Finally, the geometry can by used in finite element codes to simulate the grain interactions. The subject of the dissertation is analysis of grain interactions within a polycrystalline metal sample the model of which is based of an experimental dataset. The aim of the dissertation is to find correlations between the morphology of grain structure (grain sizes and orientations, grain boundary orientations, grain misorientations) and grain interactions in the regime of elastic deformations and, possibly, plastic and transformation deformation processes.