Date of Award

Winter 2017

Project Type

Dissertation

Program or Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Marko Knezevic

Second Advisor

Irene J. Beyerlein

Third Advisor

Todd S. Gross

Abstract

Growing demands for materials with enhanced and superb characteristics increase the difficulty and the amount of research necessary to be conducted in many different areas of expertise. The vast field of computational mechanics represents a significant source of valuable solutions to many of these challenges and can provide a smoother transition in the process when a new material is introduced. Experimental techniques are not always able to measure the localized material features due to the very complicated deformation conditions. As an alternative approach, full-field models are developed, such the ones contained in this dissertation that can bridge this gap and provide source of significant insights. The crystal plasticity finite element models (CPFEM) developed under this dissertation are presented and discussed through several specific case studies, which establish the fundamental microstructure-property relationships that describe in particular the deformation behavior of novel multilayer metallic lamellar microstructures composed of Zirconium-Niobium and Magnesium-Niobium layers. These lamellar material systems exhibit extraordinary strength while preserving ductility and they are promising candidates for application in many industries, such as nuclear and automotive. Different formulations of the 3D multiscale models were numerically implemented to investigate the origin and the development of the microstructural features that occured during the fabrication process of these lamellar composites. In particular, the orientation stability of nanocrystalline Zirconium and the formation of strain localizations were investigated during accumulative roll bonding process. Furthermore, the work contained in this dissertation describes the first attempt to incorporate the confined layer slip (CLS) model into CPFE, which greatly contributes to fundamental understanding of how Magnesium-Niobium nano-layered composites deform elastically and plastically at nanometer length scales. Next, significant efforts were put into investigating a mechanism of deformation twinning. This deformation mechanism governs the mechanical behavior of many polycrystalline metals, particularly those with low symmetry crystal structures. Deformation twins are represented as lamellar inclusions in the granular microstructures, and overall the material behaves as a composite. Hence, a novel modeling approach, which explicitly models the formation and thickening of a twin lamella within a crystal plasticity finite element framework was developed. The model represents a unique numerical procedure which is able to relate spatially resolved fields of stress and strains with microstructural changes during a twin formation and thickening. This approach was applied to study the twin formation and thickening in cast Uranium and Magnesium alloy AZ31. In AZ31 the effects of dislocation density on a twin propagation were investigated, as well as the influence of the double twin formation on the material’s fracture behavior. Overall, the presented work in my dissertation provides a powerful predictive simulation tool that could be used in many subsequent studies contributing to the further advancements in the field of computational material science.

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