Design And Experimental Verification Of Flexible Skin Based On Super-elastic SMA

Different from traditional aircraft,the morphing aircrafts can timely and intelligently change its geometric shape to change its aerodynamic layout according to the environment during flight,so as to achieve higher flight efficiency and adaptive ranges.As one of the key technologies of morphing wing,flexible skin is different from the traditional skin of fixed wing.When the wing is deformed,the flexible skin of the morphing wing not only needs to transfer and bear aerodynamic loads,but also needs to have the ability of smooth and continuous in-plane deformation to make corresponding deformation and adjustment with the wing.Especially for some wing with large deformation modes(such as span-change,chord-change),the intelligent flexible skin should meet the following requirements: First,the skin needs to have a small in-plane stiffness.Second,the skin needs to have a large out-of-plane stiffness.Third,the skin needs to have a smooth aerodynamic surface.Finally,the skin needs to have a large deformation capacity to comply with the wing deformation.In this paper,a flexible skin core layer structure with one-dimensional large deformation capability is proposed by combining the U-type honeycomb structure and NiTi shape memory alloy(SMA)based on the above four requirements for flexible skin.And in this paper the in-plane mechanical properties and deformability of U-type honeycomb structure for flexible skin based on super-elastic NiTi shape memory alloy are studied by theoretical,numerical and experimental methods.The research content and results are as follows:(1)The theoretical analysis of mechanical properties of zero-Poisson U-type ratio honeycomb structure based on NiTi-SMA in small deformation stage.Firstly,on the basis of the beam model,the force-displacement relationship of the U-type honeycomb structure in the stage of linear elastic small deformation is deduced theoretically by the energy method;Then,the force-displacement relationship of the structure with considering the material nonlinearity in the small deformation stage is derived;Finally,the theoretical solution under small deformation is verified by the finite element method.And the comparison results show that the two solutions are in good agreement in the small deformation stage.(2)The nonlinear theoretical analysis of mechanical properties of zero-Poisson U-type ratio honeycomb structure based on NiTi-SMA in large deformation stage.In order to study the in-plane mechanical properties of the U-type honeycomb structure under large deformation,in this paper,the force-displacement relationship with considering geometric nonlinearity of the U-type honeycomb structure is derived based on the Euler–Bernoulli beam theory.And then the force-displacement relationship of the structure under the consideration of geometrical nonlinearity and material nonlinearity is derived using the same method;Finally,the theoretical solutions are verified by the finite element method,and the comparison results show that the prediction results of the theoretical model derived in this paper are in good agreement with the finite element results in the large deformation stage.(3)Experimental analysis of zero-Poisson U-type ratio honeycomb structure based on NiTi-SMA.In order to verify the theoretical model above and further study its deformation capacity,in this paper,tensile tests with different global strains are performed and the experimental results are compared with the theoretical prediction results.From the comparison results,the theoretical solutions are in good agreement with the experimental solutions,therefore,the theoretical model in this paper can be used to predict the mechanical behavior of the U-type honeycomb structure based on NiTi-SMA.And the experimental results show that the recoverable global strain of the U-type honeycomb structure core layer based on NiTi-SMA exceeds 60% when the original material strain reaches 4.3%...