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 well-known structural instability characteristic of thin-walled 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 unidirectional laminates and an empirical expression useful for design purposes, comprising 4-ply symmetric laminates, are presented with validation accomplished using finite element analysis.