Morphing of symmetric cross-ply cylindrical shells by minimising the Brazier moment: Optimised hinge folding

Aileen G Bowen,Giovanni Zucco,Paul M Weaver

doi:10.1016/j.tws.2020.107122

Abstract

Aerospace and industries where both localised compliance and weight savings play a central role in design can benefit from using flexible hinges. These morphing structures use no mechanical hinges for folding. They fold by exploiting the limit point, i.e. the Brazier moment, of a geometrically nonlinear structural response characteristic of thin-walled beams under bending. Therefore, a smaller Brazier moment induces smaller non-classical stresses in the hinge during folding.Two aspects make cross-ply laminates attractive for designing flexible hinges. Firstly, the difference between the Brazier moment of an optimal symmetric generic laminate and that of an optimal symmetric cross-ply is relatively small. Secondly, cross-ply laminates do not exhibit extension-shear or bend-twist couplings which can induce complex deformations which can present challenges during design, especially considering that available analytical solutions of the Brazier moment neglect their effects. Driven by these premises, this work contributes to the preliminary design of flexible hinges by offering an analytical solution of the optimum symmetric cross-ply laminate for minimising the Brazier moment, which is subsequently validated through geometrically nonlinear finite element analysis. Moreover, this work provides insights into the prediction of the folding load considering the effects of local buckling instabilities.

Highlights

Structures in Nature are able to temporally change their shape to accomplish a broad variety of functions using their intrinsic structural properties
It must be noted that the geometrically non-linear static analysis with imperfections (GNIA) model includes a small geometrical imperfection corresponding to the first buckling mode, i.e. local buckling
The solution shows that the optimum laminate has stacking sequence [0 90 0] and its volume fraction is an algebraic function of material orthotropy

Summary

Introduction

Structures in Nature are able to temporally change their shape to accomplish a broad variety of functions using their intrinsic structural properties. Seed-bearing pine cones disperse their seeds by changing from a close to an open configuration as a response to humidity changes. They achieve such shape morphing thanks to the composite anisotropic nature of their structure [1]. The multi-functional ability of Nature to change shape has not been yet fully exploited by engineered-structures. Morphing, engineered-structures attempt to eradicate this shortcoming. Their potential applications include diverse engineering fields such as aerospace [2], automobile [3] and wind energy [4]. Flexible hinges belong to a vast subfield of morphing structures known as deployables [5] with applications including deployable booms for aerospace applications [6,7,8], see Fig. 1, and the concept of a deployable wing by Lachenal et al

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