Researchon Bistabilityof Composite Thin-shel Structure Considering Hygrothermal Effect

Bistable thin-shell is a new type of spatial structure that can be driven by an external load from one steady state to another steady state without the need for external force maintenance.This kind of structural material has the advantages of light weight,good mechanical properties and good deformability,and has wide application prospect in the fields of foldable structure,energy collector and adaptive structure.Bistable thin cylindrical shell structure is composite material composed of fiber and matrix,the fiber and the matrix elastic modulus,shear modulus,Poisson ratio,volume ratio of fiber and matrix,fiber orientation,number of layers,layers,thin cylindrical shell geometry parameters and initial geometric imperfections and other factors may affect the bistable structure.The temperature and humidity of the application environment can reduce the material properties and mechanical properties of the structure,and then affect the bistable characteristics of the structure.In order to solve the above problems,this paper studies the second steady-state characteristics of the composite thin shell structure by means of theoretical analysis and finite element simulation.The main contents and results are as follows:1.Based on the theory and energy principle of classical laminates,a two-parameter theoretical model of bistable thin cylindrical shell structure is established.The analytic expression of strain energy of symmetrical laying and anti-symmetrical laminated bistable thin cylindrical shell structure is deduced.Based on the example analysis,the strain energy curves of the thin shell structures under different parameters of two kinds laying are obtained,then the second steady state condition is predicted,the anti-symmetrical laminated thin cylindrical shell structure second steady-state analytical solution and the crimp radius bistable condition are derived;2.The analytic expression of the strain energy of the anti-symmetrical laminated cylindrical shell is deduced by considering the boundary effect.The effect of the hydrothermal effect on the bistability of the anti-symmetrical laminated cylindrical shell is analyzed.The influence of the damp heat effect on the second steady-state twist rate of the anti-symmetrical laying thin shell is predicted by a numerical example;3.The finite element analysis model of thin shell structure was established by ABAQUS software.The transition from initial steady state to second steady state was simulated,and the effects of geometric parameters such as fiber volume ratio,laying angle and structure size on bistable conditions and second steady state properties are given.The influence of the hydrothermal effect on the second steady-state characteristics of the anti-symmetric ply-laid thin shell is obtained by simulating the steady state transition process of the bistable structure under the coupling field of temperature and humidity.The simulation results are in good agreement with the theoretical prediction.