Analysis Of Creep Buckling And Optimization For Laminated Plates And Of Laminated Cylindrical Shells

In this thesis, the viscoelastic laminated plates and cylindrical shells are investigated. The optimization of creep buckling and deformation for viscoelatic laminated plates and the creep behaviors of the laminated cylindrical shells are studied. The main research contents and results are given as follows. The optimal analysis of buckling and deformation for viscoelastic laminated plates subjected to uniaxially in-plane compression and simply supported at edges are performed. The instantaneous critical load, durable critical load and stiffness of durable deformation for postbuckling, with the effect of transverse shear deformation considered, are adopted as design indexes of the laminated plates. The method to formulate these design indexes involves the application of Laplace transformation to equilibrium equations and the solution of nonlinear governing equations for postbuckling analysis by quasi-elastic approach respectively. Five types of lamination configurations are considered, and the variation features of each design index with ply angle are examined.In the analysis of quasi-static deformation of viscoelastic laminated circular cylindrical shell in axial compression, internal pressure, external pressure, hydrostatic pressure and torsion, Donnell shallow shell assumption and Kármán-Donnell geometrical nonlinear relationship are used. By applying Laplace transformation and corresponding numerical inverse transformation, the time-dependent variation features for deformation, circumferential membrane force and stress with different loading modes are examined. Boron fiber/epoxy and glass fiber/epoxy composite laminated circular cylindrical shells are involved in the analysis. In order to determine the calculation parameter in a reasonable way for the algorithm of DAC numerical inverse transformation based on Fourier series, an optimal model is developed and satisfactory results are given.The critic buckling loads of viscoelastic laminated circular cylindrical shells under axial compression are investigated based on the theory of classic buckling by means of combination of analytic with numerical approach. The generalized eignvalue problem in phase domain to determine the critic axial load is derived in the basis of Donnell type governing equations and boundary conditions. Applying the theorems of asymptotic value and initial value for Laplace inverse transformation leads respectively to the instantaneous elastic critic loads and durable critic loads. The features of two types of critical loads with ply angle and stacking sequence as well as geometrical parameters are described and Available conclusions are drawn.Based on the Donnell's shell theory, the creep buckling behavior, in the form of limit point, is investigated for viscoelastic laminated circular cylindrical shells under uniformly axial compression with geometrical imperfections. Quais-elasticity approach is applied to the analysis of end-shorting following elapsed time and the critic time is determined at which a snap-through of end-shorting occurs. Glass/epoxy composite is involved in the study, the mechanism for the influence on the behavior of delayed buckling, for ply mode, the amplitude of imperfection and boundary conditions as well, is examined by the discussion on the sensitivity of imperfection for corresponding elastic counterpart.