Date of Award

3-2025

Document Type

Thesis

Degree Name

Master of Science in Materials Science

Department

Department of Engineering Physics

First Advisor

Adib J. Samin, PhD

Abstract

The impact of crystallographic orientation, grain boundaries, and vacancies on the shock behavior of aluminum was investigated using molecular dynamics simulations. Shock loading in the [001], [011], and [111] directions was explored, revealing anisotropic behavior in shock speed, melting, dislocation density, and unique phase changes. The Hugoniot elastic limit in the [100], [110], and [111] directions was calculated as 23.2 GPa, 24 GPa, and 18.4 GPa respectively. These results were found to be an order of magnitude larger than the compressive yield strength computed at equilibrium. Additionally, metastable melting in the [011] and [111] directions occurred roughly 1000 K below the melting temperature predicted by the phase diagram. The role of both twist and tilt grain boundaries was assessed. Differences in the particle velocity profile were seen for most grain boundaries, but only for particle speeds ≤1.5 km/s, with the type and magnitude of impact varying between grain boundaries. Additionally, the presence of vacancies, both randomly distributed and clustered, led to a decrease in shock speed with a larger decrease in shock speed recorded at higher vacancy concentrations. The change in shock speed, relative to a defect free cell, exhibited a dependence on the configuration of the defects. Melting was also found to occur at lower pressures for increasing vacancy concentrations. These findings highlight the significant role of microstructure and crystallographic directions in the behavior of FCC metals, such as aluminum, under extreme loading conditions. Given aluminum’s critical role in defense and aerospace applications, understanding its response to shock loading is essential for optimizing material performance. This knowledge directly informs the design of systems subjected to extreme conditions, including high-speed weapon systems and reentry vehicles, where material selection must balance structural integrity with SWAP constraints.

AFIT Designator

AFIT-ENP-MS-25-M-253

Comments

An embargo was observed for posting this thesis.

This work is marked Distribution A, Approved for Public Release. PA case number 88ABW-2025-0237

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