Research On Realization Mechanism And Some Key Technologies Of Smart Morphing Aircraft Structures

The smart morphing aircraft which can autonomicly change its aerodynamic shape in flight to improve flight efficiency, increase maneuverability and optimize adaptability in different flight environments with variable tasks, is widely considered as an revolutionary concept and technique which could achieve new breakthrough of the future aviation technology. Surrounding the realization mechanism and key technologies of smart morphing aircraft structures, this dissertation carried out a series of studies including the basic design theory and method of smart morphing structures for aicrafts, the multi-physics coupling properties and characterizations of smart materials, the design principles and experimentations of new high-performance actuators based on smart materials, the mechanism and optimum design of superelastic composite skin structures with compliant deformation ability, and so on. The main research contents and contributions are listed as follows:1. A basic research framework of "Smart Morphing Aircraft Structural Mechanics" was proposed. And we established the smart extension cantilever wing model with time-varying boundary conditions, which is a time-varying nonlinear fourth order hyperbolic equation with approximate solution solved through dimensionless processing and Galerkin method. The smart morphing structures of head section based on SMA all-azimuthal deflectable actuator and two-motors differential bevels all-azimuthal deflectable mechanism were designed. And we built their system dynamic models and nonlinear control system models, made system simulations and prototype experiments of the smart morphing head section structures, and tested its aerodynamic characteristics through wind tunnel experiments. A variable swept wing structural scheme was proposed by using the single-crank and double-rockers mechanism. And aim at the synchronization problem of its both sides of rockers, we established a unified model of the single-crank and double-rockers mechanism and a mathematical optimization model of its synchronization performance. The approximate empirical formulas and design curves of this synchronization performance optimization solution of the single-crank and double-rockers mechanism was obtained by introducing the rockers synchronism hypothesis and symmetry assumptions of utmost position, and combined with a large number of systematic mechanism simulation studies. This work provided some theoretical references and technological suggests for structural design and analysis of smart morphing aircraft. 2. The thermo-mechanical coupling characteristics of shape memory alloy (SMA) smart materials under constraint condition, incomplete phase transformation and dynamic loading within a range of middle and low strain rates were respectively explored, based on the in-depth research of SMA quasi-static thermo-mechanical coupling characteristics. The experiments indicated that the characters were different between the first time constraint loading and the followed persistent loading, that means the impact of starting and ending temperatures of martensitic reverse transformation after martensite detwinning plastic deformation is greatly variant with that after stress-induced martensite transformation plastic deformation. Some experiments also measured the "temperature memory effect" existed in the SMA incomplete martensite reverse transformation process, and found that the restarted phase transition temperature always defered for 3K to the break temperature of last heat cycle. Besides, some experiments tested the strain rate relativity of SMA under tensile loading with the middle and low strain rates, and observed that the stress yield plateau under quasi-static tensile loading disappeared and there was significant positive correlated function between the stress-strain curve slope of plastic deformation segment and strain rates. These research results have important theoretical significance and application value for the properties modeling and application development of SMA smart materials under complex thermo-mechanical coupling loading. Further more, we built the unified dynamics model of SMA smart electromechanical systems based on the Tanaka-serial constitutive models and multi-bodies dynamics theory, and its convenience illustrated by giving some design examples. The SMA action velocity and steady state accuracy were also effectively improved by gives a composite control method for SMA smart electromechanical system.3. The "SMA smart materials-electric motor hybrid actuator" concept was proposed by combination of respective merits of SMA actuators and motors. And through system dynamics modeling and analysis of the parallel pattern and the series-to-parallel pattern, a SMA-motor hybrid linear actuator prototype was developed. Aim at the electric-thermal heating difficulties of thick SMA wire actuators for its small resistance, a new type of composite electric-thermal heating technology was invented by electrifying both the SMA wire and the enameled wire winded around the SMA wire. And a simplified thermodynamic model which showed a good agreement with experiment results was established to provide a method for control system modeling of SMA wire actuators using this new type of composite electric-thermal heating technology.4. For the urgent need of flexible skin with large compliant deformation properties of smart morphing aircraft, a "superelastic honeycomb composite skin structure" principle and optimum design was presented by introducing compliant mechanism idea to the design of cellular structures. Based on linear elastic theory, some equivalent elastic modulus formulas of symmetrical hexagonal honeycomb core structure were obtained, and the snake-like ring configuration superelastic honeycomb structures with single-axis large compliant deformation characters and the concave hexagonal configuration honeycomb structures with negative Poisson's ratio characters were designed through size parameters optimization and structural technical optimization. The equivalent modulus formulas and optimal design methods of the snake-like ring configuration superelastic honeycomb structures and the negative Poisson's ratio superelastic honeycomb structure was gained, and its theoretical correctness verified through the experimental tests.