A new IMPROVED HIGH-ORDER THEORY is presented to investigate the dynamic behavior of SANDWICH PANELs with flexible core. Shear deformation THEORY is used for the face sheets while the three-dimensional elasticity THEORY is used for the core. Displacements in the core are assumed as polynomial with unknown coefficients. Inertia forces, moments of inertia and shear deformations in the core and the face sheets are taken into consideration. Unlike the previous IMPROVED THEORY, the in-plane normal and shear stresses in the core are considered. The governing equations and the boundary conditions are derived by Hamilton's principle. Closed form solution is achieved using the Navier method and solving the eigenvalues. The numerical results of present analysis are compared with the available numerical or theoretical results in the literatures. It indicates that the present new modified THEORY is more accurate than the other developed theories for SANDWICH PANELs. The variations of the non-dimensional natural frequency with respect to the various geometrical and material parameters are investigated.

In this paper, linear elastic buckling analysis of rectangular composite SANDWICH PANEL with composite laminate faces and symmetric functionally graded material (FGM) core is presented. Unidirectional steady in-plane forces and simply supported boundary conditions are applied on the faces’ edges only. Hamilton principle and functional method are used to derive equilibrium equations, which are usually minimum functional of stored energy. In the mathematical formulation a new IMPROVED HIGHer-ORDER SANDWICH PANEL THEORY (IHSAPT) was used. First shear deformation THEORY (FSDT) is used for faces. Core displacement in various directions is modeled by polynomial function with indeterminate coefficients. It is assumed that the core is able to sustain shear and normal in-plane stresses. Temperature and humidity effects are neglected and the FGM core is modeled symmetrically. Finally, the effects of aspect ratio, thickness to side ratio, core materials’ modulus ratio, and various kinds of FGM distribution functions and powers on the critical buckling load are investigated. The numerical results show, that the effects of in plane stresses in the thick functionally graded cores on the critical buckling load cannot neglected. Also, the effects of type of FGM distribution functions and powers on the critical buckling load are considerable.

In this study, free vibration and static bending analysis of curved SANDWICH PANEL with magneto-rheological (MR) fluid layer in sheets have been studied. SANDWICH PANEL that is studied is double curved with simply support boundary condition and it is under bending load. In ORDER to derive the governing equations of motion, an IMPROVED HIGH ORDER SANDWICH PANEL THEORY and Hamilton's principle are used for the first time. After comparing with similar results in the domain of this issue and ensure that the accuracy of the derived equations, the effect of magnetic field on the frequency of the PANEL has been investigated. The effects of magnetic field intensity and changing the geometric parameters such as aspect ratio, thickness of MR layer, radius of curvature and thickness ratio on the characteristics of vibration and deflection have been studied. In the free vibration analysis section, the obtained results showed that the natural frequency of PANEL increases by increasing the magnetic field, also increases by increasing the PANEL aspect ratio, and decreases by increasing the core thickness to PANEL thickness ratio. Likewise the obtained results showed that the natural frequenciy for the case of double curved PANEL is more than single curved and flat PANEL. In the static bending analysis section, obtained results showed that the natural deflection of the PANEL decreases by increasing the magnetic field, increases by increasing the radiuses of curvatures ratio, and increases by increasing the core thickness to PANEL thickness ratio. Therefore, by changing these parameters, the natural frequency and deflection of the system, can be changed in the desired range, and also by having a controllable magnetic field in the system, the natural frequency and deflection of the system can be controlled.

A novel geometrically nonlinear HIGH ORDER SANDWICH PANEL THEORY considering finite strains of SANDWICH components is presented in this paper. The equations are derived based on HIGH ORDER SANDWICH PANEL THEORY in which the Green strain and the second Piola-Kirchhoff stress tensor are used. The model uses Timoshenko beam THEORY assumptions for behavior of the composite face sheets. The core is modeled as a two dimensional linear elastic continuum that possessing shear and vertical normal and also in-plane rigidities. Nonlinear equations for a simply supported SANDWICH beam are derived using Ritz method in conjunction with minimum potential energy principle. After obtaining nonlinear results based on this enhanced model, simplification was applied to derive the linear model in which kinematic relations for face sheets and core reduced based on small displacement THEORY assumptions. A parametric study is done to illustrate the effect of geometrical parameters on difference between results of linear and nonlinear models. Also, to verify the analytical predictions some three point bending tests were carried out on SANDWICH beams with glass/epoxy face sheets and Nomex cores. In all cases good agreement is achieved between the nonlinear analytical predictions and experimental results.

In this paper, the behavior of free vibrations of the thick SANDWICH PANEL with multi-layer face sheets and an electrorheological (ER) fluid core using Exponential Shear Deformation THEORY were investigated. For the first time, Exponential shear deformation THEORY is used for the face sheets while the Displacement field based on the second Frostig's model is used for the core. The governing equations and the boundary conditions are derived by Hamilton’ s principle. Closed form solution is achieved using the Navier method and solving the eigenvalues. Primary attention is focused on the effects of electric field magnitude, geometric aspect ratio, and ER core layer thickness on the dynamic characteristics of the SANDWICH plate. The rheological property of an ER material, such as viscosity, plasticity, and elasticity may be changed when applying an electric field. When an electric field is applied, the damping of the system is more effective. The effects of the natural frequencies and loss factors on the dynamic behavior of the SANDWICH plate are studied. The natural frequency of the SANDWICH plate increases and the modal loss factor decreases. With increasing the thickness of the ER layer, the natural frequencies of the SANDWICH plate are decreased.

In this research paper, an IMPROVED THEORY is used for buckling analysis of SANDWICH truncated conical shells with thick core and thin functionally graded material face sheets and homogeny core and with temperature-dependent properties. Section displacements of the conical core are assumed by cubic functions, and displacements of the functionally graded material face sheets are assumed by first-ORDER shear displacements THEORY. The linear variations of temperature are assumed in the through thick. According to a power-law and exponential distribution the volume fractions of the constituents of the functionally graded material face sheets are assumed to be temp-dependent by a third-ORDER and vary continuously through the thickness. In other words to get the strain components, the nonlinear Von-Karman method and his relation is used. The equilibrium equations are obtained via minimum potential energy method. Analytical solution for simply supported SANDWICH conical shells under axial compressive loads and thermal conditions is used by Galerkin’s solution method. Analysing the results show that the critical dimensionless axial loads are affected by the configurations of the constituent materials, compositional profile variations, thermal condition, semi-vertex angle and the variation of the SANDWICH geometry. Numerical modeling is made by ABAQUS finite element software. The comparisons show that the present results are in the good and better agreement with the results in the literature and the present finite element modelling.

In this study, single-objective and multi-objective optimization of curved SANDWICH PANEL with composite face sheets and magneto-rheological core have been done to maximize the first modal loss factor and minimize the mass by using genetic algorithm. The studied SANDWICH PANEL was curved with simply support boundary condition. In ORDER to derive the governing equations of motion, an IMPROVED HIGH ORDER SANDWICH PANEL THEORY and Hamilton's principle were used for the first time. The face sheet thickness, core thickness, fiber angles and intensity of the magnetic field have been considered as optimization variables. In single-objective optimization, the optimized values of variables were calculated. The results showed that the structures tend to have thick core and thin face sheets which seems physically true. As the magneto-rheological fluid placed in the core, it has a significant effect on the increasing of the modal loss factor. For the multi-objective optimization the Pareto front of optimal technique was presented. Then for the first time at this field, the set of optimal points are selected based on TOPSIS method and it was showed that in the case of similar size and mass, modal loss factor of double-curved PANEL is more than sigle-curved.

Protective steel doors are widely used in buildings due to their HIGH resistance against the impact loads. However, its heavy weight has been always considered as a major drawback for these doors. In this paper, a new optimized stiffened impact-protective steel door incorporating SANDWICH PANEL with aluminum foam core (OSSA) is examined. This door consists of two face sheets, main and secondary stiffeners, and aluminum foam as the inner core. In ORDER to optimize the door, at first the rigidity and weight functions of the stiffened steel door were extracted. Then an optimal door weighing 42% less than the primary door was obtained. Due to the HIGH energy absorption capacity of the combined foam core and stiffened steel door structure, the use of aluminum foam core in the optimized steel door was proposed. By doing numerical analysis, and depending on the thickness of the face sheet of OSSA, 20 to 32% reduction in the maximum displacement was observed. The results also showed that, with 67% increase in the peak overpressure, OSSA has kept almost the same maximum displacement as that of the steel door without an aluminum foam. In other words, by using aluminum foam core in the optimized stiffened door, the door will resist 67% more impact load.

In this study, the frequency response of rectangular SANDWICH plates with multi-layer face sheets and electrorheological (ER) fluid cores is investigated. The assumed electro-rheological fluid as a core is capable of changing the stiffness and damping of structures. In modelling the SANDWICH PANEL implemented for the first time, first-ORDER shear deformation THEORY and the second Frostig's model are applied for the face sheets and thick cores, respectively. The SANDWICH PANEL under study is supposed to simply support boundary in all edges, and the Galerkin approach is implemented for discretizing the problem. In the result section, impacts of various parameters such as electric field, aspect ratio, the thickness of the ER layer, and thickness ratio on vibrational characteristics of the structure are discussed in detail. The obtained results HIGHlight the notable effects of the electric field on natural frequencies, which can make the structure flexible within the desired range. It is also pointed out that the dynamic behavior and stability of the system can be controlled by changing the magnitude of the ER fluid layer.

In this study, an IMPROVED HIGH-ORDER THEORY is presented for buckling analysis of SANDWICH conical shell with thin FGM face sheets and homogenous soft core. First shear deformation THEORY (FSDT) used for the face sheets and cubic functions are assumed for the transverse and in-plane displacements of the core. The nonlinear Von-Karman type relations are used to obtain the strain components. The equilibrium equations are derived via principle of minimum potential energy. Analytical solution for static analysis of simply supported SANDWICH conical shells under axial in-plane compressive loads is performed by using Galerkin’ s solution. The comparisons show that the present results are in the good and better agreement with the results in the literature results.