Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Stone, Tonya W.

Committee Member

Lim, Hyeona

Committee Member

Banicescu, Ioana

Committee Member

Peters, John F.

Committee Member

Walizer, Laura E.

Date of Degree

8-12-2016

Document Type

Dissertation - Open Access

Major

Computational Engineering (Program)

Degree Name

Doctor of Philosophy

College

James Worth Bagley College of Engineering

Department

Computational Engineering Program

Abstract

This work aims to develop and implement a linear elastic grain-level micromechanical model based on the discrete element method using bonded contacts and an improved fracture criteria to capture both intergranular and transgranular microcrack initiation and evolution in polycrystalline ceramics materials. Gaining a better understanding of the underlying mechanics and micromechanics of the fracture process of brittle polycrystalline materials will aid in high performance material design. Continuum mechanics approaches cannot accurately simulate the crack propagation during fracture due to the discontinuous nature of the problem. In this work we distinguish between predominately intergranular failure (along the grain boundaries) versus predominately transgranular failure (across the grains) based on grain orientation and microstructural parameters to describe the contact interfaces and present the first approach at fracturing discrete elements. Specifically, the influence of grain boundary strength and stiffness on the fracture behavior of an idealized ceramic material is studied under three different loading conditions: uniaxial compression, brazilian, and four-point bending. Digital representations of the sample microstructures for the test cases are composed of hexagonal, prismatic, honeycomb-packed grains represented by rigid, discrete elements. The principle of virtual work is used to develop a microscale fracture criteria for brittle polycrystalline materials for tensile, shear, torsional and rolling modes of intergranular motion. The interactions between discrete elements within each grain are governed by traction displacement relationships.

URI

https://hdl.handle.net/11668/20001

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