Aircraft Wing Morphing Using Auxetic Structures

Abstract

Cellular materials exhibit two key properties: structures and mechanisms. This allows for the design of structures using cellular materials while effectively controlling both stiffness and flexibility, based on the connectivity of the struts. This study aims to explore the in-plane flexible properties of cellular materials dominated by bending under macroscopic deformation. Additionally, it seeks to establish a method for designing a passive morphing airfoil with flexible cellular cores. The investigation focuses on airfoils featuring re-entrant and S-shaped cellular cores, analyzing their behavior under static loads by examining the deformation of the cellular cores subjected to aerostatic loads. In the context of the airfoil's deformation with flexible cellular cores under aerostatic loading, shear emerges as the predominant deformation mode for the cores of the airfoil. Wings of conventional aircraft are optimized for only a few conditions, not for the entire flight envelope. Therefore, it is necessary to develop the morphing airfoil with smart structures for the next generation of excellent aircraft. In this project, this was made possible using, re-entrant and S-shaped auxetic structures as a member of the meta- material family, with negative Poisson's ratio to enable an effortless passive morphing mechanism as it has high flexibility along in-plane direction (chord-wise). The 3D CAD Models of Re-entrant and S-shaped auxetic airframes were designed and analyzed. Initially, Static Structural analysis is performed on both airframes to observe the structure’s behavior, and design modification and optimization are performed in different iterations. With a reduction in maximum equivalent stress by 20%, the Re-entrant airframe exhibits lower stress and hence more flexibility. The wings were modeled with a span of 1m using auxetic airframes, air pressure was generated using CFD analysis with MACH 0.45. Finally, the fluid-structure interaction was done by importing the air pressure and performing static structural analysis for the structural performance of wings using auxetic airframes. It was found that Re-entrant auxetic wing showed an increase of 9.99% in load carrying capacity, accompanied by a decrease of 389 grams of weight when compared to S-shaped auxetic wing. Considering the deformation of the airframe with flexible cellular cores under a load, the re-entrant honeycomb core shows the highest flexibility in shear and causes lower stress than the S-auxetic cores. This implies that the re-entrant honeycomb core has the potential for passive morphing.