High strain gradient deformation states in elastic-plastic single crystals: Theory, simulations and experiments

In this work, high strain gradient deformation states in elastic-plastic single crystals are studied. Chapter 1 provides the background of current research. Chapter 2 presents the analytical solutions to stresses and Airy's stress functions around a cylindrical void in single crystals with regular hexagonal yield surfaces. Chapter 3 is on the deformation states of cylindrical voids in face-centered cubic (FCC) single crystals. Crystal lattice rotation in aluminum single crystal under plane strain condition is measured using electron backscatter diffraction (EBSD) technique to reveal different slip sectors in the region close to the cylindrical void and to validate the theoretical predictions. Finite element solutions of stresses, strains and crystal lattice rotations are given. Experimental and analytical studies of wedge indentation into FCC single crystals are presented in Chapter 4 to reveal dislocation structures due to the high strain gradient. Lattice curvature is calculated from the EBSD data of aluminum and copper single crystals. The geometrically-necessary dislocation (GND) density and yield strength in different sectors for each of these crystals are determined. The yield strength maps reveal heterogeneous hardening behavior of the crystals. Chapter 5 is on simulation of indentation. Finite element solutions to both cylindrical indentation and wedge indentation are given. Comparison of numerical solutions and experimental data is made. Chapter 6 is on the application to materials which have potential uses in microelectromechanical systems (MEMS). Mechanical property characterization of a nano-particle reinforced copper-matrix composite thin film material prepared by electrocodeposition is studied. Chapter 7 presents conclusions and suggestions for future work.