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Hierarchical structures of aligned carbon nanotubes as low-density energy-dissipative materials

Citation

Raney, Jordan Robert (2012) Hierarchical structures of aligned carbon nanotubes as low-density energy-dissipative materials. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:05072012-134317580

Abstract

Carbon nanotubes (CNTs) are known to have remarkable properties, such as a specific strength two orders of magnitude higher than that of steel. It has remained a challenge, however, to achieve useful bulk properties from CNTs. Toward that goal, here we develop low-density bulk materials (0.1-0.4 g cm-3) entirely or nearly entirely from CNTs. These consist of nominally-aligned arrays of CNTs that display a dissipative compressive response, with a notable stress-strain hysteresis. The compressive properties of CNT arrays are examined in detail. This analysis reveals interesting features in the mechanical response, such as strain localization (resulting from a gradient in physical properties along the height), recovery after compression, non-linear viscoelasticity, and behavior under repeated compression that depends on the strain of previous cycles (similar to the Mullins effect in rubbers). We observe that in compression the energy dissipation of these materials is more than 200 times that of polymeric foams of comparable density.

Next, materials based on CNT arrays are studied as exemplary of hierarchical materials (materials with distinct structure at multiple length scales). Hierarchical materials have pushed the limits of traditional material tradeoffs (e.g., the typical trend that increased strength requires increased weight). Techniques are developed to separately vary the structure of CNT arrays at nanometer, micrometer, and millimeter length scales, and the effects on the bulk material response are examined. Structure can be modified during CNT synthesis, such as by varying the composition of the flow gas or by manipulating the input rate of chemical precursors; it can also be modified post-synthesis, e.g., by the in situ synthesis of nanoparticles in the interstices of the CNT arrays or by the assembly of multilayer structures of multiple CNT arrays connected by polymeric or metallic interlayers.

Finally, a mathematical model is applied to capture the complexities of the mechanical response. This one-dimensional, multiscale, bistable spring model is able to match the global stress-strain response as well as local effects such as strain localization and Mullins-like behavior. A technique is developed to reliably discern the model's material parameters based on in situ optical data from the experiments.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:carbon nanotubes; foams;
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Awards:Demetriades-Tsafka-Kokkalis Prize in Nanotechnology or Related Fields, 2012
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Daraio, Chiara
Thesis Committee:
  • Daraio, Chiara (chair)
  • Johnson, William Lewis
  • Bhattacharya, Kaushik
  • Ravichandran, Guruswami
Defense Date:5 March 2012
Funders:
Funding AgencyGrant Number
Army Research Office--Institute for Collaborative BiotechnologiesW911NF-09-D-0001
Army Research OfficeNational Defense Science & Engineering Graduate fellowship
Record Number:CaltechTHESIS:05072012-134317580
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05072012-134317580
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7009
Collection:CaltechTHESIS
Deposited By: Jordan Raney
Deposited On:08 May 2013 18:36
Last Modified:12 Apr 2017 00:01

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