Characteristics And Mechanism Of Wrinkling In Membrane Structures

This dissertation focuses on the wrinkling of membrane structures.We investigate the wrinkle characteristics and underlying mechanism by using experimental methods,theoretical analyses,and numerical simulations,taking into account the microstructures in membrane,the interaction between membrane and substrate,and the dynamic of membrane structure.The following results are obtained:(1)The wrinkling mechanism of a microstructured membrane is revealed.We obtain the wrinkle patterns of the membrane with periodically arranged holes under stretching by numerical simulation.We measure the wavelength and amplitude of wrinkles and analyze the influence of holes.We also examine the buckling modes of the microstructured membrane and reveal the underlying wrinkling mechanism.It is shown that the microstructured membrane may have two wrinkling mechanisms: structure buckling and microstructure buckling.The competition between both mechanisms results in the various wrinkle patterns of the microstructured membrane.(2)For the membranes with periodically arranged microstructures,when the wrinkling is triggered by the structure buckling,the microstructured membrane can be homogenized as a uniform membrane.We analyze the wrinkle characteristics and mechanism of a two-end clamped uniform membrane under stretching,which can be made of either isotropic or orthotropic material.When the wrinkling is triggered by the microstructure buckling,the membrane with periodically arranged microstructures cannot be homogenized as a uniform membrane.In this case,we focus on the membrane made up of two materials with different elastic moduli.We experimentally demonstrate the periodic wrinkle pattern on the membrane and measure the wrinkle wavelength during stretching.Based on the stress and energy states of the periodic cell of the membrane,we reveal the underlying mechanism of wrinkling by analyzing the interaction between the two contrasted materials and obtain the scaling laws for wrinkle wavelength and amplitude.(3)For the membranes with locally arranged microstructures,we observe the varied wrinkle patterns by changing the position and size of microstructures in experiment.We analyze the bucking modes and stress distribution of the membrane related to the position of local microstructures.It is demonstrated that the membrane with locally arranged microstructures also possesses the two wrinkling mechanisms triggered by structure buckling and microstructure buckling.The critical strains of structure buckling and microstructure buckling change with the position and size of microstructures,and the transition of the two wrinkling mechanisms leads to the varied wrinkle patterns on the membrane.By designing the position and size of local microstructures,the membrane can be controlled to display a desired wrinkle pattern or even a smooth surface free of wrinkles under stretching.(4)The surface morphology of a membrane adhered to a stiff substrate with van der Waals interaction is investigated.We simulate the deforming process of the membrane under uniaxial compression by using FEM.The instability morphologies of wrinkle,buckle and fold are observed and the critical strains for the transition of different instability morphologies are obtained.By analyzing the strain energy of membrane and the interaction between membrane and substrate in postbuckling process,we also obtain the characteristics of wrinkle,buckle and fold during compressing,which are related to the interaction property and the size and material property of membrane.(5)The dynamic wrinkles on a membrane structure during motion are investigated.A shell element based on the absolute nodal coordinate formulation(ANCF)is proposed to simulate the deformation and wrinkle pattern of membrane structures undergoing overall dynamic motion and large deformation.Following the scheme of isoparametric element,we adopt a curvilinear coordinate system as the undeformed Lagrangian coordinates and utilize the Green-Lagrange strain tensor with respect to the curvilinear frame to characterize the deformation energy of the shell element.The element mass matrix also keeps constant during simulation.The performance of the proposed shell element is validated by several static and dynamic numerical examples.We use this shell element to simulate the wrinkle pattern formation of a hexagonal membrane tensioned by a rectangular frame undergoing different overall dynamic motions.The evolution of wrinkle pattern and the dynamic wrinkle characteristics are obtained.We also discuss the effect of wrinkles on the dynamic motion of the membrane structure.