• Rossiter, Jonathan M.
• Walters, Peter
• Takashima, Kazuto
• Scarpa, Fabrizio L.

Abstract

Auxetic (negative Poisson’s ratio) configurations have been used recently to build prototypes of deployable structures using classical shape memory alloys (Nickel-Titanium-Copper). Chiral configurations, featuring three or more inter-connected spiral-wound hubs, exploit efficient tensile-rotational mechanisms. These structures offer high deployability ratios in structural elements with load-bearing characteristics. Shape memory polymers have the potential to replace conventional shape memory alloys and other stored-energy actuators, and have the attractive properties of low mass, high actuation strain, easy fabrication and tunable thermal properties. In this work we discuss how shape memory polymers (SMP) integrated into a chiral core could offer enhanced deployable characteristics and increase the efficiency of the auxetic deformations in these unusual cellular structures. We consider the spiralwound fundamental component needed for SMP n-chiral prototypes and present test results showing actuation motion of expanding SMP deployable structures. The angle of attachment of struts to hubs can be varied in order to tune the mechanical stiffness and compressibility of the deployed structure. The balance between axial loading in radial connected struts and flexural loading in tangentially-connected struts can also be matched to the material properties and tailored to the application. Applications likely to benefit from these structures include lightweight elements for structural engineering applications, deployable structures for space applications and implantable medical devices.

Topics

• polymer
• nickel
• copper
• titanium
• Poisson's ratio