Award Date

August 2016

Degree Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Mechanical Engineering

First Committee Member

Brendan J. O'Toole

Second Committee Member

Mohamed Trabia

Third Committee Member

Jaeyun Moon

Fourth Committee Member

Robert Hixon

Fifth Committee Member

Moses Karakouzian

Number of Pages

143

Abstract

New additive manufactured (AM) materials have the potential of optimizing the geometry and microstructure of complex components to enhance their structural integrity while creating them quickly. However, the behavior of AM materials under extreme dynamic loading conditions is not fully understood. This is especially important in many applications. For example, spacecraft components may be impacted by micrometeorites at hyper velocities of multiple kilometers per second, inducing extreme dynamic loading.

One type of AM material is created by melting and solidifying metal along a specified path. Depending on the geometry, additional streams will be deposited side-by-side. This process affects the microstructure of the AM part. More voids will exist in a typical AM part as compared to its forged counterpart. While some researchers studied the mechanical characteristics of AM metallic components under static and some dynamic loading, no comparable research for behavior under extreme dynamic loading could not be found.

The objective of this thesis is to experimentally and computationally study the behavior of titanium alloy, Ti-6Al-4V (Grade 5), under shock loading by comparing forged and layered titanium to the AM titanium. In these experiments, the target materials were subjected to hypervelocity impact using a two-stage light gas gun. A Photonic Doppler Velocimetry (PDV) diagnostics system was used to measure free-surface velocity on the back of each target configuration. The experimental measurements were well documented and can be used to describe the behavior of these materials under shock loading. In addition to velocity measurements, physical damage and spall crack formation were monitored. The experimental measurements were used to validate computational simulations of the experiments.

It was determined that AM and forged titanium produce similar velocity profiles during the early stage of impact, with the AM targets exhibiting spall at lower velocities and the multi-layered stacks exhibiting vibrations between plates. Simulations of single layer forged and AM materials provide a good match to experimental data. This study will provide insights into the failure mechanisms of AM titanium under extreme dynamic loading.

Keywords

additve manufacturing; hypervelocity; impact properties; photonic doppler velocimetry; simulation; titanium

Disciplines

Engineering | Mechanical Engineering

Language

English


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