Date of Completion

4-25-2019

Embargo Period

4-24-2020

Keywords

Molecular Dynamics, Shock, Dislocation, Spallation, Damage Resistance, Spall Strength

Major Advisor

Dr. Avinash M. Dongare

Associate Advisor

Dr. Mark Aindow

Associate Advisor

Dr. Harold Brody

Associate Advisor

Dr. Seok-Woo Lee

Associate Advisor

Dr. Ying Li

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Design of next-generation high strength metallic materials for damage-resistant applications relies on a fundamental understanding of the deformation mechanisms and failure behavior of these materials under dynamic loading conditions. The dynamic strength of metals is typically characterized based on the “spall strength” defined as the peak tensile pressure the metal can withstand prior to failure. For pure FCC metals, the capability to increase the spall strength is limited due to insufficient microstructural features that can be used to tailor/modify the deformation and failure behavior under dynamic loading conditions. The current understanding of the role of grain boundaries and deformation twinning in BCC metals, however, is still in its infancy. Another promising strategy to design high strength microstructures is the engineering of nanoscale interfaces in alloy microstructures that may alter the nucleation and evolution of defects/damage. Such strategies have been successfully demonstrated experimentally in FCC/BCC alloy microstructures. A critical challenge in engineering these microstructures, however, is the lack of understanding on the role of interfaces on the spall failure behavior. Such an understanding is particularly challenging using experimental techniques due to the short time and length scales of the processes of nucleation and evolution of defects/damage. Therefore, the goal of this dissertation is to carry out a systematic study using classical molecular dynamics (MD) simulations to investigate the role of structure and energies of grain boundaries in BCC microstructures as well as the structure, size and distribution of FCC/BCC interfaces on the twinning/de-twinning behavior as well as the damage nucleation (void nucleation and growth) behavior under shock loading conditions. Such understanding will enable to identify key microstructural descriptors of the interfaces that determine the spall strength, and aid in the design of nanocrystalline Ta and Cu/Ta microstructures with enhanced spall strengths for damage-tolerant applications.

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