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Proceedings Paper

Modeling actuation forces and strains in nastic structures
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Paper Abstract

Nastic structures are capable of three dimensional shape change using biological principles borrowed from plant motion. The plant motor cells increase or decrease in size through a change in osmotic pressure. When nonuniform cell swelling occurs, it causes the plant tissue to warp and change shape, resulting it net movement, known as nastic motion, which is the same phenomena that causes plants to angle their broad leaf and flower surfaces to face light sources. The nastic structures considered in this paper are composed of a bilayer of microactuator arrays with a fluid reservoir in between the two layers. The actuators are housed in a thin plate and expand when water from the fluid reservoir is pumped into the actuation chamber through a phospholipid bilayer with embedded active transport proteins, which move the water from the low pressure fluid reservoir into a high pressure actuation chamber. Increasing water pressure inside the actuator causes lateral expansion and axial bulging, and the non-uniform net volume change of actuators throughout the nastic structure results in twisting or bending shape change. Modifying the actuation displacement allows controlled volume change. This paper presents an analytical model of the driving and blocking forces involved in actuation, as well as stress and strain that occurs due to the pressure changes. Actuation is driven by increasing osmotic pressure, and blocking forces are taken into consideration to plan actuator response so that outside forces do not counteract the displacement of actuation. Nastic structures are designed with use in unmanned aerial vehicles in mind, so blocking forces are modeled to be similar to in-flight conditions. Stress in the system is modeled so that any residual strain or lasting deformation can be determined, as well as a lifespan before failure from repeated actuation. The long-term aim of our work is to determine the power and energy efficiency of nastic structures actuation mechanism.

Paper Details

Date Published: 5 April 2006
PDF: 10 pages
Proc. SPIE 6173, Smart Structures and Materials 2006: Smart Structures and Integrated Systems, 61731O (5 April 2006); doi: 10.1117/12.658585
Show Author Affiliations
Luke A. Matthews, Univ. of South Carolina (United States)
Victor Giurgiutiu, Univ. of South Carolina (United States)


Published in SPIE Proceedings Vol. 6173:
Smart Structures and Materials 2006: Smart Structures and Integrated Systems
Yuji Matsuzaki, Editor(s)

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