Studies On Folding And Unfolding Deformation Behavior Of Membrane Structure

Large space membrane vehicles need to be folded before launching to meet their high volume efficiency.A large amount of creases can be generated by the folding of membrane.These creases have a significant effect on the shape and performance of membrane structure,which are the typical failure mode of high-precision membrane structures,such as the inflatable deployable antenna.On the other hand,the properties of nanoscale membrane structures,such as graphene membrane,are closely related to their surface configurations.The performance control of many devices need to be achieved through configuration design(such as folding).However,the folding deformation mechanism of membrane structure is still not clear,and the theoretical analysis method of folding deformation needs to be further studied.Therefore,this paper focuses on the study of folding and unfolding deformation behavior of membrane structure,and extends the method to study folding characteristics of graphene membrane.It has important theoretical and engineering guiding significance for the folding and unfolding design of membrane structure and its configuration regulation.This paper proposes a large deformation beam model under plane strain condition to study the folding deformation of membrane structure at first.The power-law hardening material relation is chosen.The critical folding force and folding space are predicted.The variation of folding space and folding shape versus folding force are obtained.The expanding law of plastic region and the variation law of folding critical angle are simulated.The variation of stress field in crease region is analyzed in the end.The unfolding deformation of creased membrane structure is studied.A large deformation beam model under plane strain condition that considers the rotational stiffness of crease is proposed.The influences of initial crease angle,bending stiffness and crease rotational stiffness on the unfolding deformation are discussed.The relationship between bending deformation,crease angle change and tension deformation of creased membrane structure during the unfolding is then obtained.The numerical analysis model of crease with initial complicated stress and strain information is established.The stress variation of the crease in the unfolding process is studied,the relationship between the tensile load and the unfolding configuration is obtained,and the effect of the creases on the wrinkling deformation of membrane structure is analyzed in the end.The experiments of folding and unfolding deformation of membrane structure are performed.The folding mechanical responses of membrane with different thickness are tested.The variation of folding force and residual folding space with thickness are studied.The relationship between the minimal folding space and the residual folding angle is tested.Based on the optical noncontact measurement technology,the relationship between tension load and unfolding shape of creased membrane structure is obtained.The crease rotational stiffnesses for the different minimal folding space are then determined.The accuracy of theoretical models of folding and unfolding deformation is verified by the experiment results in the end.In the end,this paper uses the proposed theoretical model of crease beam to predict the folding and unfolding deformation of graphene membrane.The prediction of elastic property of graphene membr ane is modified based on the molecular structure mechanic model with variable stiffness Timoshenko beam.The variations of potential energy,stress field and folding configuration during the folding deformation of graphene membrane are simulated by using the molecular dynamics method.Based on the plane strain beam theory,the folding shape of graphene membrane is predicted,which is consisitent with the simulated result.Based on the beam theory,the unfolding deformation characteristics of creased graphene membrane are then analyzed.Combining the microscopic mechanics method,the effect of crease on the elastic properties of graphene oxide is studied in the end.