Post-buckling Analysis Of GPLs Reinforced Cylindrical Shells

On account of its great load bearing property as well as cost-effectiveness,thin-walled cylindrical shells as a typical type of thin-walled structures have been widely used in various engineering realities.To prevent thin-walled cylindrical shells from buckling failure,which is the main failure mode of thin-walled structures,grid-stiffened cylindrical shells are more commonly used nowadays.As a newborn graphene derivative,graphene platelets(GPLs)exhibit remarkable mechanical,electrical and thermal properties.Hence the additive of a small number of GPLs could significantly enhance the mechanical properties of the traditional composites.Consider that most thin-walled cylindrical shells have to bear combined axial compression and lateral pressure(or hydrostatic pressure)during working,it is very meaningful and of vital importance to perform post-buckling analysis on the GPLs reinforced composite circular cylindrical shells under combined loads.And the results of analysis could provide reference as well as guidance for engineering applications.This article performed elaborate and precision post-buckling analysis on functionally graded graphene platelets reinforced composite(FG-GPLRC)cylindrical shells and grid stiffened shells under axial compression combined hydrostatic pressure based on a unified shell theory,which is applicable for either thin or moderately thick shells as it combined higher order shear deformation theory and classical thin-walled theory.To improve the accuracy of postbuckling calculation,reasonable equivalent conditions are elaborately constructed for the boundary condition of double-clamped.And the symmetric post-buckling mode is distinguished to the asymmetric mode.The main works in this dissertation includes:1.The governing equations of shell are established based on a unified shell theory.By combining an analytical procedure and the Galerkin’s method,a semi-analytical method is developed to solve the equations.The obtained results from the present solutions agree well with those of existing theoretical and experimentally observed data.And the Halpin-Tsai micromechanical model is employed to build the material model of GPLs reinforced porous composite,so that the effective mechanical properties under different GPLs and pores distribution mode could be obtained conveniently.2.Post-buckling analysis of FG-GPLRC porous cylindrical shells is performed.The effects of the geometry and the material properties and loading condition on the post-buckling behavior and knockdown factor(KDF)of the FG-GPLRC porous cylindrical shell are explored.The discrepancies between the results of the classical thin-walled shell theory and those of the moderately thick shell theory become enormous while the shell is relatively short or thick.And the trend that knock down factor varies with the shell thickness is influenced significantly by the hydrostatic pressure load.3.By applying the principle of superposition and homogenization method,the equivalent stiffs of ribs are calculated efficiently,and based on which the post-buckling behaviors of FGGPLRC porous cylindrical shells with different types of grid stiffeners are examined.The inplane boundary conditions of displacements are neglected during solving procedure.The numerical results find that among four basic types of grid the orthotropic one could improve the post-buckling bearing property most,and the numbers and cross section properties of stiffeners nearly circunferential direction have a main influence on the post-buckling behaviors of grid stiffened cylindrical shells under dominantly hydrostatic pressure.