Grain Subdivision and Microstructural Interfacial Scale Effects in Polycrystalline Materials

Abstract

The major objective of this research is to develop a unified physically-based representation of the microstructure in f.c.c. crystalline materials to investigate finite inelastic deformation and failure modes and scenarios at different physical scales that occur due to a myriad of factors, such as texture, grain size and shape, grain subdivision, heterogeneous microstructures, and grain boundary misorientations and distributions. The microstructurally-based formulation for inelastic deformation is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs), and grain boundary dislocations (GBDs). This dislocation density based multiple-slip crystal plasticity formulation is then coupled to specialized finite-element methods to predict the scale-dependent microstructural behavior, the evolving heterogeneous microstructure, and the localized phenomena that may contribute to failure initiation for large inelastic strains. The SSD densities provide a representation of cell-type dislocation microstructures and their related processes. The GND densities provide an understanding of the scale-dependent deformation behavior of crystalline materials as a function of grain and aggregate sizes. The GBD densities are formulated to represent the misfit dislocations that arise due to lattice misorientations across GBs, and to provide a framework to investigate the phenomena associated with the grain boundary orientations and distributions. This provides a local criterion of how GB interfaces, such as triple junctions are potential sites for failure initiation and localized behavior. The evolution of the GNDs is used to predict and understand how crystallographic and non-crystallographic microstructures relate to intragranular and intergranular deformation patterns and behavior. Furthermore, a clear understanding of how GB strength changes due to microstructural evolution is obtained as a function of microstructural heterogeneities that occur at different physical scales.