Multi-stable composite twisting structure for morphing applications

Abstract

Conventional shape-changing engineering structures use discrete parts articulated around a number of linkages. Each part carries the loads, and the articulations provide the degrees of freedom of the system, leading to heavy and complex mechanisms. Consequently, there has been increased interest in morphing structures over the past decade owing to their potential to combine the conflicting requirements of strength, flexibility and low mass. This article presents a novel type of morphing structure capable of large deformations, simply consisting of two pre-stressed flanges joined to introduce two stable configurations. The bistability is analysed through a simple analytical model, predicting the positions of the stable and unstable states for different design parameters and material properties. Good correlation is found between experimental results, finite-element modelling and predictions from the analytical model for one particular example. A wide range of design parameters and material properties is also analytically investigated, yielding a remarkable structure with zero stiffness along the twisting axis.

HCI meets Material Science

“…Extensive research into multi-stability has been conducted within composite materials [50,125,144,145,183,184]. The snap-through phenomenon occurs when a structure is forced to transition from one equilibrium, which is stable under small perturbations, to another (usually by an external force), by transitioning through a region of instability.…”

A novel span-wise morphing trailing edge concept

“…the laminate ply angle β for all the spar strips, the initial pre-bend curvature κ initial in the middle and tip spars and the twist angle ϕ [19,25]. The stable equilibrium configurations are determined when the first derivative of the strain energy Π is zero and the second derivative of Π is greater than zero.…”

“…1) leads to the ZTS of the SMTE. There are several ways to model prestress effects in the spars for instance the two-step analysis procedure used by Lachanel et al [18,25] and the effective coefficients of thermal expansion (CTE) method by Daynes et al [19] which requires only one model and reduces the modelling complexity. In this study, the latter method using an effective CTE is chosen and an equivalent gradient temperature field across the laminate thickness is modified to model the prestress strain caused by flattening the initial pre-bend laminates.…”

CARAPACE: A novel composite advanced robotic actuator powering assistive compliant exoskeleton preliminary design

“…The work presented here draws upon modelling worked by Lachenal et al [17]. The MCT behaviour is analysed through the evolution of its strain energy.…”

“…The main idea is to exploit flexible structures to develop Compliant "Morphing" Mechanisms [14][15][16] with embedded actuators to be integrated at joint level. In particular, here this is done utilizing the Multistable Composite Structures of the kind presented by Lachenal et al [17] and Pirrera et el. [18][19][20] .…”