Micro-buckling Of Functionally Graded Thin Elastic Memory Composite Plate

Due to the limitation on the size of spacecraft,the space deployable structures must be folded before they are launched into space.When the spacecraft is in orbit,the structures will be unfolded to perform their functions.These deployable structures are made of elastic memory composite(EMC).And they have high structural properties and shape memory characteristics,as well as very high strain capability.Hence,this type of functional materials has great potentials in future space deployable structures.EMC consists of continuous fibers embedded in a shape memory polymer(SMP)matrix.At elevated temperature(above the glass transition temperature),the SMP matrix becomes very soft and cannot provide sufficient support for the fibers during the folding process of EMC structures.As a result,the compressed fibers are prone to occur micro-buckling deformation.This process acts as a stress relief mechanism during folding,and allows the material to reach very high curvatures without permanent damage.Hence,micro-buckling of fibers in soft matrix is considered to be an enabling mechanism that can be exploited for enhanced multifunctional behavior.Small buckling deformation of fibers effectively prevents the permanent damage of material and makes the structure work better.The goal of this study is to characterize the micro-buckling behavior and understand the mechanics of this type of composite.Firstly,the micro-buckling mechanism of EMC thin plate with uniformly distributed fibers under pure bending is investigated.A three-dimensional theoretical model is established by using the energy method with the consideration of the shape and size effect of fibers on the shear strain of matrix.The results show that the micro-buckling degree of the structure can be controlled by tailoring the four parameters,namely the thickness of the plate,the modulus ratio of matrix to fiber,the diameter of fibers,and the fiber volume fraction.Secondly,the micro-buckling mechanism of the functionally graded EMC thin plate under pure bending is investigated.The fiber volume fraction is assumed to change linearly along the thickness of the plate.A three-dimensional model for the analysis of micro-buckling of functionally graded EMC thin plates is established by using the energy method.The results show that the micro-buckling degree of the functionally graded plate can be controlled by tailoring the five parameters,namely the thickness of the plate,the modulus ratio of matrix to fiber,the diameter of fibers,the fiber volume fraction,and the form of fiber distribution.Finally,the finite element model of post-buckling deformation of EMC thin plate with uniformly distributed fibers is established.The equal proportion reduction model is discussed.The results show that the equal proportion reduction model and its boundary conditions verify the theoretical model of post-buckling deformation of EMC thin plates with uniformly distributed fibers established in this paper.The results obtained in this paper provide a theoretical basis and numerical simulation technology for accurately predicting the folding behavior of EMC thin plates.At the same time,it also provides a theoretical basis and technical reserve for the design and manufacture of space deployable structures.In addition,the theoretical study on the micro-buckling mechanism of functionally graded EMC thin plates is provided in order to improve the folding resistance of EMC deployable structures,which is of great significance to the optimization design and engineering application of functionally graded EMC materials.