Date of Completion

3-6-2019

Embargo Period

3-4-2020

Keywords

Shock, Molecular Dynamics, Mesoscale Modeling, Spall

Major Advisor

Dr. Avinash Dongare

Associate Advisor

Dr. Mark Aindow

Associate Advisor

Dr. Seok-Woo Lee

Associate Advisor

Dr. Ying Li

Associate Advisor

Dr. Volkan Ortalan

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The capability to predict the impact tolerance of next generation lightweight metallic materials for protective armor application requires fundamental understanding of the deformation and failure behavior of these materials under dynamic loading conditions. Loading conditions of impact/shock result in complex stress states that range from uniaxial compression to tension at high strain rates ranging from 105 s-1 to 1010s-1. The deformation response of these materials is determined by the capability of the microstructures to nucleate dislocations and failure response is determined by the creation of weak sites for void nucleation during uniaxial expansion. A critical challenge in the understanding of mechanisms of plastic deformation and onset of dynamic failure (spallation) is the short time scales associated with these phenomena that limit the capabilities of experimental characterization methods to investigate these mechanisms. As a result, this dissertation focuses on investigation of micromechanisms of interaction, evolution and accumulation of defects and damage during shock compression and spall failure at atomic scale using molecular dynamics (MD) simulations. The MD simulations, due to their high computational cost, are limited to system sizes that are upto a few hundred nanometers and timescales of tens of picoseconds. These limitations result in strain rates of ~1010 s-1 under shock loading conditions using reasonable computing resources. The dissertation demonstrates the capability of newly developed quasi-coarse-grained dynamics (QCGD) method to retain atomistic mechanisms of evolution of microstructure during shock compression and spall failure at time and length scales which are beyond the capability of MD simulations i.e at mesoscales.

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