Date Available

8-1-2024

Year of Publication

2024

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Chemical and Materials Engineering

First Advisor

Dr. Paul F. Rottmann

Abstract

Due to their wide range of attractive functional properties (such as low thermal conductivity and low density) porous materials are utilized in a variety of applications. In order to characterize these properties and others, the intrinsically heterogeneous microstructures of these materials need to be taken into account. These microstructures result in interactions across multiple length scales spanning several orders of magnitude. This makes the creation of robust computational models and straight-forward predictions of mechanical properties difficult for porous materials. With this in mind, this dissertation aims to provide experimental mechanical and deformation information spanning the length scales of interest for a porous carbon fiber material. Ex situ mechanical testing in combination with digital image correlation (DIC) was utilized to investigate the macroscale mechanical properties and mesoscale deformation behavior. Distinct, orientation-dependent properties were obtained through both tensile and compressive testing. Loading parallel to the average fiber orientation resulted in greater elastic moduli and greater toughness during tensile loading. Conversely, loading perpendicular to the average fiber orientation resulted in greater toughness during compressive loading. These definitive behaviors are thought to be caused by either reversible (fiber bending and sliding) or irreversible (fiber and fiber contact failure) damage accumulation methods. The impact of complex geometries (e.g. cracks and through-holes) on the compressive results has also been investigated utilizing the same setup. From the findings of the ex situ work, it was determined that additional in situ investigation was necessary to more comprehensively understand the deformation behavior. A new testing protocol utilizing interrupted compression testing in conjunction with in situ micro-computed tomography (microCT) was created to answer these questions. Through this technique both high-resolution and lower-resolution microCT scans were completed to visualize the samples at the fiber level and mesoscale, respectively. The combination of these results allowed for greater understanding of how both the fiber level and mesoscale change and interact during compressive deformation.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.307

Funding Information

This work was supported by NASA Kentucky Space Grant Consortium under NASA award 80NSSC20M0047.

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