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Rate and Microstructure Effects on the Dynamics of Carbon Nanotube Foams

Citation

Thevamaran, Ramathasan (2015) Rate and Microstructure Effects on the Dynamics of Carbon Nanotube Foams. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9DB7ZRG . http://resolver.caltech.edu/CaltechTHESIS:10162014-104834622

Abstract

Soft hierarchical materials often present unique functional properties that are sensitive to the geometry and organization of their micro- and nano-structural features across different lengthscales. Carbon Nanotube (CNT) foams are hierarchical materials with fibrous morphology that are known for their remarkable physical, chemical and electrical properties. Their complex microstructure has led them to exhibit intriguing mechanical responses at different length-scales and in different loading regimes. Even though these materials have been studied for mechanical behavior over the past few years, their response at high-rate finite deformations and the influence of their microstructure on bulk mechanical behavior and energy dissipative characteristics remain elusive.

In this dissertation, we study the response of aligned CNT foams at the high strain-rate regime of 102 - 104 s-1. We investigate their bulk dynamic response and the fundamental deformation mechanisms at different lengthscales, and correlate them to the microstructural characteristics of the foams. We develop an experimental platform, with which to study the mechanics of CNT foams in high-rate deformations, that includes direct measurements of the strain and transmitted forces, and allows for a full field visualization of the sample’s deformation through high-speed microscopy.

We synthesize various CNT foams (e.g., vertically aligned CNT (VACNT) foams, helical CNT foams, micro-architectured VACNT foams and VACNT foams with microscale heterogeneities) and show that the bulk functional properties of these materials are highly tunable either by tailoring their microstructure during synthesis or by designing micro-architectures that exploit the principles of structural mechanics. We also develop numerical models to describe the bulk dynamic response using multiscale mass-spring models and identify the mechanical properties at length scales that are smaller than the sample height.

The ability to control the geometry of microstructural features, and their local interactions, allows the creation of novel hierarchical materials with desired functional properties. The fundamental understanding provided by this work on the key structure-function relations that govern the bulk response of CNT foams can be extended to other fibrous, soft and hierarchical materials. The findings can be used to design materials with tailored properties for different engineering applications, like vibration damping, impact mitigation and packaging.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Carbon nanotube foams; synthesis of carbon nanotube foams; morphological characterization; synchrotron x-ray scattering; electron microscopy; impact testing technique; geometric moire transducer; high-speed imaging; dynamic characterization; microstructure effects; structure-function relations; rate effects; deformation mechanisms; multiscale models; wave propagation; vertically aligned carbon nanotubes; helical carbon nanotubes; microarchitectured carbon nanotubes; microscale heterogeneities
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Daraio, Chiara
Thesis Committee:
  • Ravichandran, Guruswami (chair)
  • Bhattacharya, Kaushik
  • Kochmann, Dennis M.
  • Pellegrino, Sergio
  • Daraio, Chiara
Defense Date:23 September 2014
Funders:
Funding AgencyGrant Number
Institute for Collaborative BiotechnologiesW911NF-09-0001
Record Number:CaltechTHESIS:10162014-104834622
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:10162014-104834622
DOI:10.7907/Z9DB7ZRG
ORCID:
AuthorORCID
Thevamaran, Ramathasan0000-0001-5058-6167
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8699
Collection:CaltechTHESIS
Deposited By: Ramathasan Thevamaran
Deposited On:23 Feb 2016 20:43
Last Modified:10 Apr 2017 23:36

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