Morphing Mechanisms Based on Nonlinear Helical Composite Elements

Abstract

Tailoring structural nonlinearities offers the potential to design well-behaved nonlinear structures with increased functionality and enhance the performance of modern engineering structures. In light of this concept, this research focuses on the behaviour of structural assemblies of nonlinear morphing elements. A compliant, multistable, reconfigurable mechanism is introduced, which consists of nonlinear morphing structural elements assembled in a truss-like configuration.
Existing compliant mechanisms rely on flexible members and their elastic deformations to achieve multistability, but their range of motion is restricted by strength limitations. The compliant mechanism developed in this research uses morphing elements as the flexible members. These elements are composite structures of a double-helix architecture that can change shape and undergo large deformations while maintaining load-carrying capability and structural integrity. The variable geometry and customizable nonlinear stiffness characteristics of the double-helices enable the mechanism to be tailored and a variety of behaviours to be developed.
For the study of the mechanical characteristics and design space of this mechanism, a simple truss structure has been chosen. Two different approaches have been employed for the structural analysis of the mechanism: (i) an energy approach to identify the stable configurations of the truss across its workspace; (ii) a path-following method, the modified-Riks method, to explore the force-displacement space.
Both the multistability and reconfigurability of this mechanism have been explored. The mechanism’s multistable characteristics and response upon application of a load at the apex have been investigated parametrically. Additionally, the reconfigurability of the mechanism has been explored. Based on the ability of the double-helical elements to switch twist direction when in fully extended state, the mechanism is able to change behaviour and operate in different modes, whilst maintaining its connectivity and mobility.
Finally, a prototype is manufactured and tested for the validation of the results from the analytical model.

Date of Award	24 Mar 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Alberto Pirrera (Supervisor) & Mark Schenk (Supervisor)