Research On Numerical Methods Of Composite Laminated/Sandwich Plates Based On The C~0-type Global-local Higher-order Theory

Laminated composite structures have been widely used in many engineering fields such as aerospace,ocean,and automobile duo to their high strength,fatigue-resistence,and designability.However,owing to the the heterogeneity and anisotropy through the thickness direction,the mechanical characteristics of the laminated composite structures are more complex than that of traditional single-layer structures.Moreover,the interlaminar shear stiffness of the adhensive joints in lamianted composite structures is weak,which is prone to interlalinar damage and delamination failure.Interlaminar transverse shear stress is one of the key factors for the onset delimination in laminated composite structures.Therefore,it is of great significance for accurate modeling of laminated composite structures and for accurate prediction of through-the-thickness stress distributions,especially for the transverse shear stresses.For the mechanical analysis of laminated composite structures,this thesis developed several C0-type global-local theories.Moreover,the laminated plate elements are proposed for bending,hygrothermal,buckling and vibration of laminated plates and softcore sandwich plates.The present works are summarized as follows:1.Inthis thesis,an accurate C0-type third-order global-local theory considering transverse normal thermal deformation(MGLTC)is proposed for thermo-mechanical analysis of multilayered composite beams.The transverse normal thermal deformation is involved in the transverse displacement field.Although transverse normal defonnation is considered,the number of displacement parameters is not increased.Employing three-dimensional(3D)equilibrium equations and Reissner mixed variational theorem(RMVT),the accurate transverse shear stresses are obtained.Based on the proposed global-local model,the thermo-elasticity behaviors of multilayered composite beams are investigated,and the analytical solutions of several simply-supported laminated beams are obtained.The performance of the proposed model is assessed through different numerical examples,and the results show that the proposed model can accuratly predict the interlaminer shear stresses without any post-processing approach.2.In this thesis,based on the RMVT and the 3D equilibrium equations,a C0-type third-order global-local theory(MGLHT)is proposed for the analysis of multilayered composite plates.The outstanding advantage of the present theory is that no post-processing approach is needed to calculate the transverse shear stresses.It is significant that the second-order derivatives of in-plane displacement variables have been eliminated from the transverse shear stress fields,such that the low-order linear plate elements are easily constructed.By analyzing bending problem of multilayered composite plates,the accuracy of MGLHT and the efficiency of three-node triangular element based on the MGLHT are fully verified.3.In this thesis,a C0-type fifth-order global-local theory(IGLM)for laminated composite plates with general configurations is proposed.The initial in-plane kinematic assumptions of IGLM are obtained by superimposing the local fifth-order displacement functions on the global third-order displacement functions.and the transverse displacement is assumed to be linear across the thickness.Applying the free traction conditions of transverse shear stresses,the first-order derivatives of transverse displacement are eliminated from the kinematic assumptions of the proposed theory.so that C0-continuity shape functions are only required for the finite element modelling.Thus,based on the global-local model,the quadratic eight-node isoparametric element is proposed to analyze bending and hygrothermal behaviors of laminated composite plates with general configurations.4.In this thesis,a new C0-type third-order global-local theory(MZZT)is proposed,the kinematic assumptions of the proposed theory are obtained by superimposing a third-order local function on the first-order shear deformation theory.The new local function can provide a proper zigzag contribution to the in-plane displacements,which is more suitable for analysis of soft-core sandwich plates.Based on the 3D equilibrium equations and the RMVT,the accurate transverse shear stresses are obtained.Moreover,the second-order derivatives of in-plane displacement variables are not involved in the transverse shear stress components,such that the low-order linear plate elements are easily constructed.Based on the MZZT,finite element formulation of four-node quadrilateral element is developed for bending and buckling analysis of softcore sandwich plate,and the three-node triangular element is proposed to investigate free vibration of softcore sandwich plate.Performance of the proposed model is fully assessed by several numerical examples.Moreover,numerical examples show that the accuracy of transverse shear stresses have a significant effect on the prediction of critical loads of softcore sandwich plates and natural frequecies of laminated composite plates with different thickness.