ORCID Identifier(s)

0000-0003-0998-7414

Graduation Semester and Year

2017

Language

English

Document Type

Thesis

Degree Name

Master of Science in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Ashfaq Adnan

Abstract

Transition metal carbides, nitrides, and borides are a group of Ultra High-Temperature Ceramic (UHTC). Owing to their remarkable properties of the high melting point, high thermal conductivity and excellent strength at elevated temperature ZrB2 based composites are of high interest for use in the high-temperature environment. It is proved that addition of SiC in ZrB2 can advance composite’s oxidation resistance, mechanical strength, fracture toughness and sintering behavior. Firstly, molecular dynamics is used to simulate crack growth under mixed mode loading in Al, SiC, and ZrB2 single crystals by considering inclined crack under uniaxial tension and crack growth angle are compared with those obtained by Maximum Stress criterion analytically. Subsequently, the role of grain boundary in the fracture is studied, and core-shell type morphology of ZrB2-SiC based ceramics is modeled using Molecular dynamics tool to demonstrate the effect of modified grain boundaries on mechanical properties of such materials. Results from molecular dynamics simulations indicated that fracture under mixed mode conditions is mainly stress based and provided the good inter-atomic potential field molecular dynamics is capable enough to generate results in good agreement with experiments and theory. Also, a morphological study of the core-shell ZrB2/SiC system revealed that increasing amount of SiC above the certain limit could have a detrimental effect on material’s strength, but it might increase fracture toughness of the system.

Keywords

Mixed mode fracture, MD, Crack propagation, ZrB2, SiC

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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