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The Deformations of Thin Nematic Elastomer Sheets

Citation

Plucinsky, Paul P. (2017) The Deformations of Thin Nematic Elastomer Sheets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9765CCT. http://resolver.caltech.edu/CaltechTHESIS:06022017-081925673

Abstract

Thin structures exhibit a broad range of mechanical responses as the competition between stretching and bending in these structures can result in buckling and localized deformations like folding and tension wrinkling. Active materials also exhibit a broad range of mechanical responses as features that manifest themselves at the microscale in these materials result in mechanical couplings at the engineering scale (thermal/electrical/dissipative) and novel function (e.g., the shape memory effect and piezoelectricity in select metal alloys and the immense fracture toughness of hydrogels). Given this richness in behaviors, my research broadly aims to address the following questions: What happens when active materials are incorporated into thin structures? Do phenomena inherent to these materials compete with or enhance those inherent to thin structures? Does this interplay result in entirely new and unexpected phenomena? And can all this be exploited to design new functions in engineering systems?

In this thesis, we explore these questions in the context of a theoretical study of thin sheets of nematic liquid crystal elastomer. These materials are active rubbery solids made of cross-linked polymer chains that have liquid crystals either incorporated into the main chain or pendent from them. Their structure enables a coupling between the mechanical elasticity of the polymer network and the ordering of the liquid crystals, and this in turn results in fairly complex mechanical behavior including large spontaneous distortion due to temperature change, soft-elasticity and fine-scale microstructure.

We study thin sheets of nematic elastomer. First, we show that thin of sheets of a particular class of nematic elastomer can resist wrinkling when stretched. Second, we show that thin sheets of another class of nematic elastomer can be actuated into a multitude of complex shapes. In order to obtain these results, we systematically develop two dimensional theories for thin sheets starting from a well-accepted first principles theory for nematic elastomers. These characterize (i) the mechanical response due to instabilities such as structural wrinkling and fine-scale material microstructure, and (ii) thermal actuation of heterogeneously patterned sheets. For the latter, we show that the theory, which comes in the form of a two dimensional metric constraint, admits two broad classes of designable actuation in nonisometric origami and lifted surface. For the former, we show that taut and appreciably stressed sheets of nematic elastomer are capable of suppressing wrinkling by modifying the expected state of stress through the formation of microstructure.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Nematic elastomers, thin sheets, wrinkling, microstructure, actuation
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Awards:Centennial Prize for the Best Thesis in Mechanical and Civil Engineering, 2017.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Bhattacharya, Kaushik
Thesis Committee:
  • Ravichandran, Guruswami (chair)
  • Pellegrino, Sergio
  • Daraio, Chiara
  • Bhattacharya, Kaushik
Defense Date:10 May 2017
Non-Caltech Author Email:plucinsp (AT) gmail.com
Funders:
Funding AgencyGrant Number
NASA Space Technology Research FellowshipNNX14AL51H
Record Number:CaltechTHESIS:06022017-081925673
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:06022017-081925673
DOI:10.7907/Z9765CCT
Related URLs:
URLURL TypeDescription
https://doi.org/10.1007/s00205-015-0871-0DOIArticle adapted for Ch. 3
https://doi.org/10.1016/j.jmps.2017.02.009DOIArticle adapted for Ch. 3
https://doi.org/10.1103/PhysRevE.94.010701DOIArticle adapted for Ch. 4
https://arxiv.org/abs/1611.00729arXivArticle adapted for Ch. 4
ORCID:
AuthorORCID
Plucinsky, Paul P.0000-0003-2060-8657
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10250
Collection:CaltechTHESIS
Deposited By: Paul Plucinsky
Deposited On:03 Jun 2017 00:03
Last Modified:16 Jun 2017 23:08

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