Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Document Type

Dissertation

Abstract

Metallic foams, or nanoporous (NP) metals as it is widely referred to in literature, with ligament sizes up to a few tens of nm show exceptional mechanical properties such as high strength and stiffness per weight ratio under different loading scenarios due to their high surface area to solid volume ratio. Therefore, they can be utilized in a wide range of applications making them of great interest to researchers. While their elasticity and yield strength have been the subject of several studies, very limited attention was given to the effect of size, strain rate, and temperature on the material plastic response. Moreover, despite the significant attention in the literature that is directed towards the development of scaling laws that relate the properties of nanoporous metals to bulk materials, the literature still lacks a specific model that predicts the material mechanical properties based on a combination of parameters capturing the effect of surface area, ligament size, relative density, strain rate, and temperature. Therefore, the effect of ligament size, strain rate, and temperature are investigated using large-scale atomistic simulations to probe the elastic response, plastic response, and deformation mechanisms of nanoporous gold under uniaxial compression and tension and up to strains in excess of 60 percent for strain rates in the range of 106 π‘ βˆ’1 and 109 π‘ βˆ’1 at temperatures between 300K and 700K. This work explores the full range of the material response, focusing on the modifications to strain hardening and densification under compression and on the ductility and failing mechanisms under tension. Additionally, by utilizing the literature reported results, scaling laws that account for the effect of surface area to solid volume ratio, ligament size, relative density, strain rate, and temperature to predict the elastic modulus, yield stress, and ultimate stress are proposed. Finally, a size, relative density, strain rate, and temperature dependent dislocation based constitutive model that describes the plastic flow in NP-Au is proposed. The results reported in this work will eventually help enhancing the design of novel metallic foams with tailored mechanical response.

Date

6-24-2021

Committee Chair

Voyiadjis, George Z.

Available for download on Thursday, June 23, 2022

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