Research On Creep Buckling And Post-Buckling For Columns, Plates And Honeycombs

In this dissertation, the synthetical influences of viscoelasticity, geometric nonlinearity and initial deflection on the creep buckling and post-buckling of columns, plates and honeycombs are investigated systematically. The results are of great importance not only in the corresponding academic theories but also in the practical engineering. The main contents and results of this dissertation include as follows:Based on the linear stability theory, the creep buckling of the viscoelastic columns with initial deflection, torsional elastic restraint and eccentricity load is analyzed. Consequently, the instantaneous critical load, the creep buckling life and the torsional elastic restraint coefficient are determined. Additionally, a semi-analytical method for creep buckling of columns is presented to analyze the creep buckling of a compressed column with initial imperfection, of which the accuracy can be controlled easily. By the present semi-analytical method, the deflection of column and the stresses of section in every time step can be obtained. And the results are comparable to that of sandwich model. By employing Kachanov's damage theory, in which the tension and compression have different contribution to the damage rate of the material, the influence of damage on creep buckling of viscoelastic column is analyzed.According to the linear viscoelastic theory and Norton's power law creep constitutive equation respectively, the failure life for creep-buckling of column with initial deflection is determined. And the results corresponding to the geometrical linearity and nonlinearity are compared with each other. The influences of initial deflection, compressive load and material parameter on the failure time for creep-buckling of column are investigated in detail. And the range of application of geometrical linear theory for the creep-buckling of column is discussed.On the basis of Kachanov's continuum damage theory and Von Karman's nonlinear theory of plates, the nonlinear equilibrium equations of plate subjected to in-plane and lateral loads are established including creep damage effect. In the Kachanov's damage evolution equation, tension and compression are assumed to have different contribution to the damage rate. With the stresses, forces and moments of the section of the plate calculated from numerical integral, the nonlinear equilibrium equations are solved by iterative method. The influences of several parameters, such as geometric nonlinearity, in-plane and lateral load, damage, as well as equivalent stress etc., on the creep post-buckling process are discussed. An orthotropic constitutive relationship and damage evolution equations of orthotropic material are derived by employing the algebra invariant theory and irreversible thermodynamics theory. The post-buckling of plate with orthotropic material is researched bade on the above damage constitutive and evolution equations.Employing the compression-bending coupling stability theory of beam-column, the elastic buckling behavior of general honeycombs subject to in-plane biaxial loading are analyzed, the critical loading expressions of two different buckling-morphologies are derived under different loading cases. The influences of the cell-edge thickness, cell angle, cell length and material properties of honeycombs on critical load are discussed. The analytical solution shows a good agreement with the numerical results obtained from the ANSYS commercial finite element program.Based on Norton's power law creep theory and the principle of free energy conservation, the creep-buckling behavior of general honeycombs subjected to in-plane uniaxial and biaxial loading are investigated respectively. The relation of the stresses and the failure time for creep-buckling is derived. The effects of the loads, cell-edge thickness, cell angle, cell length and initial imperfection of honeycombs on the response curves of the critical loading and failure time for creep-buckling are discussed.The research results in this dissertation will be helpful to understanding the behaviors of creep-buckling of columns, plates, honeycombs. The results provide the theoretical basis for safe life assessment and design of limit load for viscoelastic columns, plates and honeycombs.