Investigation On Morphing Wing Structures Based On Shape Memory Polymer Composite(SMPC) Skins And Active Honeycomb Structures

To compare with the existing aircraft, morphing aircraft can have shorter taking-off and landing distance, less fuel consumption, farther cruising distance, higher ceiling. Morphing wing technology is a transformational technology of improving the integrated performance of aircraft, which is of great significance to the development of aircraft. However, one of the key factors of morphing aircraft is light and deformable/loading integrated materials and structures. Morphing aircraft based on traditional materials and structures has large weight, complex structures, high maintenance cost. The key techniques of the realization of morphing aircraft include: changeable/loading integrated skin technology, high energy density actuator technology, adaptive structure technology, etc. Novel smart materials and structures present the characteristics of large deformation, high energy density, self-actuating, self-sensing, and provide the material foundation for the development of morphing aircraft. To solve the key technological problems of morphing aircraft, i n this paper, the author proposes one new material as changeable/loading integrated skin structures, two novel structures as driving/structural integrated adaptive structures, and three new applications to verify their feasibilities.Morphing skin structures need to follow the deformable structure, which request to have lower stiffness; at the same time, the skins should have enough stiffness to withstand aerodynamic load in flight. To solve this contradiction, this paper proposes a design of morphing skins using a variable stiffness material--Shape Memory Polymers(SMPs). This material presents high stiffness at low temperatures(glassy state), which can withstand the aerodynamic load; the stiffness is reduced drastically at high temperature(rubbery state), it can realize the large deformation. To solve the problems of toughness in low temperature and low tearing strength of thermosetting styrene based SMP resin, elastic fibers are used to enhance the mechanical properties of SMPs in this work. The Shape Memory Polymer Composites(SMPCs) with different elastic fiber contents were prepared, and analyzed by the dynamic mechanical analysis, mechanical analysis at high and low temperature and thermal response analysis. Results show that by adding elastic fibers, toughness at low temperatures, elastic modulus and strength at high temperature of SMPs are enhanced, especially, the tear strength is improved markedly, which make SMPs safe and reliable in application. In this paper, SMPC skins were used in a variable camber trailing edge wing structure. This paper is focused on the capacity of withstanding aerodynamic load of SMPC skin, as well as meeting the requirement of deformation. The static pressure distribution on the wing surface was obtained from CFD simulation analysis, and then the load was applied on the skin surface to obtain the out of plane deformation data. The results show that, the 10mm-thickness SMPC skin can satisfy the requirements at M0.6 high speed in the glassy state; it also can satisfy the condition of M0.1 in low speed flight in the rubbery state. For a morphing aircraft, morphing skin can be flexible to change the shape at low speed, and flight at high speed after it becomes hard, which verified the feasibility of application of SMPC skin structures.According to the requirements of light actuator and morphing structure of morphing aircraft, the author proposes an active honeycomb structure based on Pneumatic Flexible Tubes(PFTs) in this paper. The first case is sandwiching the PFTs between two groups of honeycombs to control the distance between the honeycombs, which is applied to morphing thickness wing structures; second case is inserting the PFTs into the honeycomb cellular to change honeycomb’s angles, which is applied to a morphing wingtip wing structure.For the first case, the PFTs can be displaced along the spanwise direction or the chordwise direction. The geometric model of PFTs geometric variations was established. The equations about the input pressure in PFTs and deformation of active honeycomb structure under different loading conditions were constructed through mechanics analysis. Prototypes of active honeycomb structure actuated by pneumatic flexible tubes were fabricated to verify the theoretical results by testing. The morphing thickness wing models with PFTs in spanwise and chordwise direction were manufactured respectively, which demonstrate the feasibility for morphing aircraft in the future.In view of the second case, two PFTs were inserted into a reentrant hexagonal honeycomb structure. The angle of the honeycombs can be changed by inflating into the tubes. The geometric model and energy model of this active honeycomb structure were established. The relationship between system input pressure and output displacement were obtained. The displacement of active honeycomb structure was also analyzed and predicted by the linear elastic model and hyperelastic model, respectively. Comparative analysis was investigated through experiments, theoretical model and finite element model. The hysteretic phenomena and energy aborted under cyclic loading conditions were analyzed by experimental method. A morphing wingtip structure was designed based on this kind of active honeycomb structure and SMPC skins. The relationship between the angle of wingtip structure and input pressure was established, which was validated by experiment. The elastic fiber reinforced SMPC skins were covered on the corner, to make the wing surface smooth and continuous during the deformation process, which can lock the wing shape as well. The demonstration verified the potential application in morphing wingtip for future aircraft design.