Deployment Behaviors Of Woven Composite Bistable Cylindrical Shells

Cylindrical shells made from woven composite with certain laminte angle can be stable both in the initial and the coiled state without any other constraints.These structures are known as bistable cylindricall shells,and have wide potential applications in space deployable structures thanks to their advantages like simple coiling structures,high deployment realibility and high packaging efficiency.The methods are needed to model the special features such as the movement of the ploy region,local buckling,and large rotation during the coiling and uncoiling processes of the woven composite bistable cylindrical shells.A systematic study on the coiling and uncoiling behaviors of the woven composite cylindrical shells is conducted in this thesis.The models for predicting the bending stiffness,the snap through behavior,the ploy region and the key parameters during the coiling and uncoiling processes are presented,and the structural characteristics of the bistable shells in the deployed state are studied.The primary contents are as follows:Bending stiffness distribution is the key to realize bistable for woven composite cylindrical shells.However,the bending stiffness predicted from classical laminate theory is larger than the real value because of the non-uniform laminate of the fiber yarns through the thickness.To predict the bending stiffness,the height and width of the yarn and the distance between the two adjacent yarns are determined using the micro-structure of the woven composite,and the geometry of the unit-cell is built then.A finite element model is presented using voxel mesh method,and the non-uniform displacement boundary conditions for the bending and twisting cases are applied using programmed method.Four-point bending test and cantilever plate bending test are conducted.Bending stiffness from the predicted model agrees well with the experimental value,and the deviation is 5.33%.Basing on the bending stiffnesses obtained from the previous section,an analytical model is proposed using the transverse and longitudinal cur vatures as the two variables,which can be used to predict the strain energy of the deformed configurations between the two stable states.The bistable mechanisms for woven composite cylindrical shells are analyzed and the critical cross section angles are presented.A two point tension loading method is proposed to investigate the snap through behaviors,which can be used to analyze cylindrical shells with subtened angle greater than 180°.Load-displacement curves for cylindrical shells with different longitudinal length are obtained numerically and experimentally.The ploy region is diffcult to model using polynomial curves directly.A method is presented to divide the ploy region into two different zones.The zone near the coiled state is known as the quasi-coiled zone,and the longitudinal curvature is the dominant parameter.The zone near the deployed state is known as the quasi-deployed zone,and the transverse curvature is the dominant parameter.The control equations for the two different zones are deduced using thin-walled shell theory.Then an analytical model is proposed combing the boundary conditions,which can be used to predict the curvature distribution and the length of the ploy region.The effects of the geometry dimensions and bending stiffnesses on the length of the ploy region are analyzed.The analytical length of the ploy region is 257.76 mm,5.58% smaller than the finite element result.For certain bending stiffness,the length of the ploy region is proportional to the arc length of the cross section.The length of the quasi-coiled zone tends to decrease,while the length of the quasi-deployed zone and the ploy region tend to increase along the increase of D12 and D66.Basing on the previous research,an analytical model is proposed assuming the coiled strain energy can be changed to the deployment kinematic energy partly.The model can be used to predict the displacement and velocity during the deployment process.Besides,a finite element model is presented to study the dynamic beha viors of the coiling and deployment processes.The coiling and deployment of the bistable cylindrical shell are tested,and the results obtained from analytical,numerical and experimental methods agree well with each other.For the bistable shell with the deployed length is 0.7m,the deployed times from the analytical model and test are 0.238 s and 0.247 s separately,and the deviation is 3.64%.The deployed time decreases along the increase of the subtended angle with the same cross section arc length,and also decreases linearly along the increase of the bending stiffness.The axial compression and the positive and negative bending characteristics of the deployed cylindrical shell are investigated using finite element method.The effects of geometric parameters and bending stiffnesses on the critical loads are studied.Then the natural frequencies are analyzed using finite element model,and the effects of geometry and bending stiffnesses are studied.Basing on the bistable cylindrical shell,a bi-shell structure using two bistable cylindrical shells is presented,which can provide new approach for deployable structures.The loads and the deformation of the bi-shell structure are analyzed using analytical model and finite element method finally.