Application Of Shape Memory Alloys In Aircraft Structural Stiffness Control

A new method based on shape memory alloys was studied to control the stiffness of structure in the context of aerodynamic heating of supersonic aircraft. And the variable-stiffness rudder structure of strengthening rib replaced by SMA strips was proposed.Taking beam structure as the research object, shape memory alloy strips were arranged on the beam structure making use of its characteristics, and the mathematical model of the stiffness control of the beam structure is given. Based on the calculation results, the stiffness control effect of the beam structure was not only related to the thickness of shape memory alloy, but also the ratio of elastic modulus. This provided a theoretical basis for application of shape memory alloys in the field of aircraft structural stiffness control.According to the model of the traditional rudder, the model of variable stiffness based on shape memory alloys was designed. And the effect of the structural stiffness was analyzed by finite element simulation. To maximize the effect of control, genetic algorithm was used to optimize the structure size.The layout method of the reinforcement of the rudder plane structure was optimized. In addition, the effect of structural stiffness control was verified by modal experiments. The results show the stiffness of the structure can be passively controlled by making use of the feature that the elastic modulus of austenitic phase is higher than that of martensitic phase under a high temperature. Besides, the first order natural frequency of the structure can increase 10% after the control system works. Furthermore, the changing trend of stiffness of the structure with the environmental temperature increasing was also studied. And an active control system was established because the phase transition of SMA could not be fully completed under the environmental temperature. The instantaneous discharge of large capacitors was used to drive the SMA in order to complete the phase transition. And the experimental results indicate the response time of the SMA can reach 15 ms. In addition, as the temperature increases, the stiffness of structure initially decreases, and then increases gradually. When the temperature is equal to the austenitic finish temperature at zero stress, the stiffness achieve maximum value. After that, it decreases slowly.