Mechanical Behavior Of Functional Graded Materials And Structures In Thermal Environment

In this thesis, three aspects are investigated, they are the effect of boundaryconstraints on the bifurcation buckling for functionally graded cylindrical shells inthermal environment, prediction of thermo-rheologic parameters of viscoelasticfunctionally graded materials and creep characteristics on axisymmetric bending ofviscoelastic functionally graded cylindrical shells and viscoelastic functionally gradedcircular plates in thermal environment. The main research contents and results aregiven as follows.Based on prebuckling consistent theory, the effect of boundary constraints on thebifurcation buckling for functionally graded cylindrical shells subjected to axialcompression and lateral pressure in thermal environment is investigated. The analyticsolution is obtained for prebuckling deformation coupling thermal and mechanicalloading as well as initial geometrical imperfects. The nonlinear eigen-value problemis derived by combining the approach of separating variables with the technique offinite difference to solve the governing equations of bifurcation buckling. Thetemperature dependence of material properties is taken into account in the analysis,the influence of temperature gradient along thickness, initial geometrical imperfection,volume fraction of material composite in the critical loads is examined with respect tosimply supported ends and clamped ends respectively. The results show thattemperature sensitivity and imperfection sensitivity under axial compressioncorresponding to clamped ends are stronger than those in simply supported ends, butbecome weaker with the increase of temperature gradient, and the volume fraction ofmaterial composite exerts little influence on imperfection sensitivity irrespective toboundary conditions at ends. Also it is revealed that the effect of boundary constraintson bifurcation buckling abates with the rise of amplitude of initial geometricalimperfections. The critical loads under lateral pressure have considerableimprovement as the reduction of length-radius ratio and the increase of the index ofthe volume fraction, the FGM cylindrical shell under lateral pressure doesn’t haveimperfection sensitivity.The Mori-Tanaka approach originally used in linearly elastic hypothesis isextended to predict the relaxation modulus and creep compliance of grain fillingcomposite materials under isothermal condition, and the validity of the extension is examined by comparing the results of prediction with numerical solution obtained onmicromechanical model. A nonlinear mixture law with respect to the volume fractionof constituents is constructed on the basis of Reuss’s linear mixture law in order toobtain the creep compliance of FGM’s, the effect of temperature can be taken intoaccount in the model. A linear interpolation approach is taken in the transition zone todetermine creep compliance. The comparison of present prediction with the resultsfrom Mori-Tanaka approach and experimental data verifies the validity of the mixturelaw given in the paper. A nonlinear simple mixed law with respect to the compositevolume content is constructed on the basis of Voigt’s linear mixture law in order topredict the other thermo-viscoelastic parameters of functionally gradient materials,and its validity is verified by comparing with experimental data and the resultsobtained from micromechanics method.Based on the Mori-Tanaka approach and the nonlinear simple mixed law, creepcharacteristics on axisymmetric bending of viscoelastic functionally gradedcylindrical shells and viscoelastic functionally graded circular plates in thermalenvironment are investigated. Respectively applying viscoelastic approach andquasi-elastic approach, the flexural deformation of viscoelastic functionally gradedcylindrical shells is analyzed under axial compression, lateral pressure and internalpressure. For viscoelastic functionally graded circular plates, the flexural deformationof the clamped and simply supported circular plates is investigated applyingviscoelastic approach.