2 research outputs found
Flexible hinges in orthotropic cylindrical shells facilitated by nonlinear elastic deformations
Flexible hinges enable the design of folding structures without using mechanisms by making use of intrinsic structural characteristics in the action of folding. This technology introduces potential benefits including weight reduction, omission of lubrication and potentially better system reliability. To achieve such technology, we exploit a wellâknown structural instability characteristic of thinâwalled structures under bending: the Brazier effect. Composite materials play a key role in this problem since they enable the critical load for folding to be tuned. Moreover, the minimisation of the Brazier moment is material dependent, offering extra degrees of freedom for morphing purposes. The present work considers the minimisation of the Brazier moment providing insights on its material dependency. For this purpose, an analytical solution for cylindrical shells made of uni
directional laminates and an empirical expression useful for design purposes, comprising 4âply symmetric laminates, are presented with validation accomplished
using finite element analysis
Morphing of symmetric cross-ply cylindrical shells by minimising the brazier moment: Optimised hinge folding
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