Publication Date

2020

Document Type

Dissertation/Thesis

First Advisor

Salehinia, Iman

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Mechanical Engineering

Abstract

Nanoporous materials have attracted attention recently because of their extensive range of possible applications. These nanoporous materials are comprised of nanowires and nodes. A node joins three or more nanowires of different orientations. Current research has focused on nanowires and nodes composed of metallic single crystals and core-shells. Nanoporous materials experience brittle failure from the rupture of the weakest feature, overloading the other remaining structural features. To alter the deformation behavior of the network nodes, a ceramic layer has been added around the metal. Coating the metallic ligaments with ceramic shell increases the buckling capacity of each ligament and further improves the overall buckling capacity of the porous material. The new material also offers significant improvement on the tribological characteristics of the porous metal, including scratch resistance and coefficient of friction. Recent developments on the mechanical properties of ceramic/metal nanolaminates have shown the co-plastic deformation of metal and ceramic for controlled design parameters. Core-shell metal/ceramic porous material may also show measurable ductility if the geometrical parameters such as the ceramic thickness, the diameter of the metallic ligaments, and the ratio of the coating thickness to the ligament diameter are carefully chosen. The models display different deformation behavior when varying the ratio of the ceramic shell to the metal core and maintaining a specific core diameter with increasing shell thickness. The tension-compression load curves show asymmetric behavior which is a symptom of differing plasticity mechanisms. In tension, the smaller core nanowires are dominated by brittle failure mediated from high stresses by the shell cracking. Once the metal core becomes the dominating volume fraction of the system, the cores deformed by dislocation glide within the core. The nodes deformed by dislocation glide for the large core, nucleated from a compression corner along with twinning. In compression, the nanowires cores exhibited failure by shear banding in small core sizes but changed to deformation twinning as the core size increases. For the node, the small core exhibited bond breaking within the ceramic layer from a tension corner. The larger core node had dislocation glide from compression corners within the core along with bond breaking in the ceramic layer from tension corners. The similarity of the yield locus and mechanical properties of the node suggest that nanoporous’ materials mechanical properties are more closely related to the node than the nanowires.

Extent

94 pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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