Zero Poisson's ratio flexible skin for potential two-dimensional wing morphing

This study presents and examines the concept of flexible skins for two-dimensional morphing applications composed of a zero-Poisson cellular core and a hyperelastic face sheet. The overall properties of the flexible skins are mainly determined by the cell structure types and parameters. The in-plane mechanical properties of three different zero-Poisson cell structures were investigated with analytical, numerical and experimental methods to determine the most suitable cell structure for two-dimensional morphing. The geometric and material nonlinearity effects on the in-plane mechanical properties of the cell structures were also discussed. The material constants of a silicone rubber as flexible face sheet were then experimentally determined and its hyperelastic behaviors were simulated to find a better boundary condition in which uniform strain and larger global strain could be obtained. 98.6% global strain for span morphing and 9.2° angle change for sweep morphing were achieved in the simulation tests of integrated skin, which validates the two-dimensional morphing capacity of the passive sandwiched skin proposed in this article. For the actuation requirement of the passive skin, a shape memory alloy (SMA) based antagonistic actuator for span morphing was developed and tested. With 11.5% global strain finally achieved, the results, to certain extent, validates the feasibility of SMA actuator application to wing span morphing.