Deployable Soft Composite Structures with Morphing and Shape Retention

Abstract

In this dissertation, the possibilities of systematically designing and constructing deployable soft composite structures utilizing smart soft actuators composed of shape memory alloy (SMA) based smart soft composites (SSCs) as the basic elements are proposed and explored.

The first part of the dissertation describes the working principles of SMA based SSC actuators and presents new basic actuators that are suitable for implementation in deployable structures. The base SSC actuator design is extended from simple bending actuators to hinge actuators and linear actuators. A brief mathematical model is described to predict the deformation of the proposed SSC actuators. These actuators with diverse and large deformation are simple to fabricate, inexpensive, lightweight and simple to actuate. Based on these advantages, soft robots such as crawling robots and compliant gripper are designed and evaluated.

In the second part, a structure based on the variable stiffness principle is integrated into the SSC actuator which can enable the proposed composite actuator to both produce a soft morphing motion and to have shape retention capability. This is accomplished by embedding low-melting-point material with heating components in a SSC actuator structure. The stiffness variation of the actuator is accomplished by melting the embedded low-melting-point material using heating components embedded in the structure. The actuator can then retain its deformed configuration with the variable stiffness structure in the high stiffness state after the low-melting-point material structure is solidified.

In the third part, deployable structures are proposed using the proposed actuators with stiffness reversible property as the basic element of the assembly. This basic actuator can be used to form modules capable of different types of deformations, and these modules can then be assembled into deployable structures. The design of deployable structures is based on three principles: design of basic actuators, assembly of modules and assembly of modules into large scale deployable structures. Various deployable structures such as a segmented triangular mast, a planar structure comprised of single-loop hexagonal modules and a ring structure comprised of single-loop quadrilateral modules are designed and fabricated to verify this approach.

The final part of the dissertation is a study of tiling techniques for use as a reference for the construction of planar deployable networks based on the proposed SSC hinge and linear actuators. A general approach to construct planar deployable networks has been proposed which can be divided into three steps: selection or design of suitable tiling, design and validation of joint connections, and construction of networks. Several possible configurations have been discussed and verified using the assembled structures.