Space Technology Research Grants

Liquid Crystal Elastomer Membranes and the Wrinkling Instability

Completed Technology Project
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Project Description

In its technology roadmap, NASA has expressed a desire to develop tailorable materials to better enable design and deployment of lightweight, efficient space structures. For instance, lightweight, easily deployable and inflatable reflectors have garnered particular interest to replace conventional unwieldy mirrors for use on space probes. Recent attempts to utilize polymer membrane technology as deployable substrate for a reflector have faced many technical hurdles: one limitation has been achieving the high surface accuracy required; another has been the presence of surface wrinkling under the complex boundary conditions necessary to pull the membrane taut. We conjecture that the wrinkling phenomenon can be limited or even suppressed completely by utilizing a novel polymer based Liquid Crystal Elastomer material as constituent for the membrane. Consequently, we propose to research the mechanics of Liquid Crystal Elastomer membranes, with emphasis on understanding the wrinkling behavior exhibited by these structures. We believe the prospect of developing a wrinkle-free membrane utilizing this material is exciting, and merits the attention and funding of NASA as it seeks to update its space technology infrastructure with innovative lightweight structures and tailorable materials. In a broader context, the interplay between structural and material non-linearities highlighted by this proposed research raises fundamental questions in mechanics worthy of thesis. In the proposal, we will show a scaling argument that supports the hypothesis. We then propose to develop a numerical scheme that can accurately capture wrinkling mechanics as well as the material nonlinearities of liquid crystal elastomers. This will enable us to investigate realistic space structure geometries, as well as novel complex shapes only possible due to use of liquid crystal elastomer material. We also propose a clamped stretching experiment to further validate our claims.

Anticipated Benefits

This project aims to address technical hurdles associated with using polymer membrane technology as a deployable substrate for a reflector. Lightweight, easily deployable and inflatable reflectors have garnered particular interest to replace conventional unwieldy mirrors for use on space probes.

Organizational Responsibility

Responsible Mission Directorate
Space Technology Mission Directorate (STMD)
Responsible Program
Space Technology Research Grants (STRG)
Lead Organization
California Institute of Technology (CalTech)

Project Duration

Start: 2014-08-01
End: 2017-06-15

Partner Organizations

Project Contacts

Primary U.S. Work Locations

California

Technology Area

Primary Technology Area:

Materials, Structures, Mechanical Systems, and Manufacturing/

12.1 Materials/

12.1.1 Lightweight Structural Materials

Technology Maturity

Start
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Applied ResearchDevelopmentDemo & Test

Technology Transitions

Project Start
Aug 2014:
Project started
Closed Out
Jun 2017:
Project closed out
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 (e.g., wrinkle suppressing membranes)? In this research, 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 finescale 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 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.

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Target Destinations

Outside the Solar System
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