Date of Completion

8-14-2020

Embargo Period

8-14-2021

Keywords

In-situ, Cryogenic Tests, Mechanical Characterization of Materials, Small-scale Mechanics

Major Advisor

Seok-Woo Lee

Associate Advisor

Bryan D. Huey

Associate Advisor

Avinash M. Dongare

Associate Advisor

Pu-Xian Gao

Associate Advisor

Barrett O. Wells

Field of Study

Materials Science and Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The mechanical properties of materials have been considered as one of the most important material properties for the development of mechanically reliable engineering products. Although some materials exhibit excellent material properties, such as electronic, magnetic, thermal, and optical properties, the materials cannot be usable in engineering applications if they are mechanically unstable in devices. Nowadays, nanotechnology allows us to make useful small-scale engineering devices, for instance, actuators of Micro-Electro-Mechanical-Systems and silicon-based electronic devices. These developments have continuously required the creation of mechanically reliable small materials that can survive during the long-term service. For the last two decades, micromechanical studies have revealed that mechanical properties could change significantly if a material dimension is reduced down to the micrometer-scale. At these small length scales, materials could be much stronger and tougher than their bulk counterpart. Therefore, it is critical to re-evaluate the mechanical properties of materials at the micrometer scale because small-scale mechanical properties are different from bulk-scale mechanical properties.

In this dissertation, we show our new development of state-of-the-art in-situ cryogenic micro-mechanical testing to investigate the mechanical properties of two different types of crystalline solids at low temperatures. First, we show how the sample dimension influences the ductile-to-brittle transition of body-centered-cubic metals. Second, we show a superelasticity of an intermetallic compound, CaKFe4As4 and its relation to superconductivity at low temperatures. We believe that these efforts provide an important insight into a fundamental understanding of the mechanical behavior of materials at the micrometer scale and at low temperatures.

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