Research On Large Storage Ratio Deployable Technology Of Cylindrical Flexible Structures

Membrane structures,a new kind of space structures developed vigorously in recent decades,is a structure form that use membrane as main material to achieve the predeterminate functions by applying pre-stress or self-rigidizing,thus have potentially broad application prospects in the fields of human life,military,aerospace,building structures and so on.During the application and development of the membrane structures,A great challenge is the wrinkling problem of the membrane.In this paper,firstly,the mechanism analysis model on the wrinkling area of membrane was studied,and then the finite element software was used to achieve the general analysis of wrinkling characteristics on the complex membrane structures.The former mainly determines the differential equilibrium equation and the stress condition equation in the wrinkling area and the latter establishs a general calculation process for membrane wrinkle characteristics.Based on extensively reading of relevant literatures,the main research contents of the thesis are as follows:In this paper,the prestress and deflection effects are firstly introduced into the post-buckling stress formula,and the strength improvement after membrane buckling is considered.Then a buckling equilibrium equation of wrinkles based on half-moment theory is proposed.The results of nonlinear buckling numerical analysis show that the half-moment theory has higher accuracy.The strain equilibrium condition in the vertical direction of the wrinkle is added to obtain the prediction formula of the half-wavelength and amplitude of the wrinkles and the principal stress expression of the membrane after buckling with shear load and prestress as variables.The validity of the nonlinear buckling numerical analysis method is verified by the experiment results.Then the nonlinear buckling numerical analysis method is used to made the parameter analysis of the rectangular membrane under shear load and the results under different parameter models are used to verify the half-wavelength,amplitude prediction formula of the wrinkles and post-buckling stress expressions have higher accuracy,and compared with the predecessor's prediction formula,the accuracy advantage is more obvious at higher prestress levels.Moreover,in comparison with previous experimental results,the formula is still has a high accuracy.According to the characteristics of the new theoretical analysis model and the shortage of the tension field theory,a method for estimating the membrane wrinkling characteristics based on the result of the tension field theory is proposed.Firstly,it is proved that the tension field theory method ignores the influence of bending stiffness on the basis of nonlinear buckling analysis method.Based on this,the strain equilibrium conditions in the vertical direction of wrinkle applied to the tension field theory method are derived,and then the prediction formula of the half-wavelength and amplitude of the membrane wrinkles based on the tension field method results is obtained.and then a general calculation process for membrane wrinkle characteristics isestablished.Finally,using the results of the rectangular membrane and hexagonal membrane under tensile load under the shear load to verify the calculation process.A cylindrical deployable flexible structure that can be used as a general structural hood or sun shield is designed,and a two-stage and multi-dimensional deployment concept is proposed for the storage ratio requirement of the flexible structure.The radial and longitudinal folding schemes are specifically designed by using the origami concept.The modal analysis of the final state structure under different air pressure and prestressing conditions proves that the structure satisfies the primary frequency requirement under the given air pressure and prestress conditions by using the finite element software.The two-stage deployment of the flexible structure is simulated,and the morphological change and the maximum principal stress value of the structure during the unfolding process are obtained.Using the above-mentioned general calculation process for membrane wrinkle characteristics to estimate the wrinkling configuration features of the deployed structure,and then predict the wrinkling configuration at the corresponding location based on estimation results.The results can be used to evaluate the shape accuracy of flexible structures,optimize structural forms and structural dynamics.