---

In this article, nonlinear bending analysis of sandwich circular plates with functionally graded face sheets subjected to transverse mechanical load is presented. The formulations are based on first-order shear deformation plate theory (FSDPT) and large deflection von Karman equations and nonlinear equilibrium equations solved by the dynamic relaxation (DR) method combined with the finite difference discretization technique. In order to verify the current work some obtained results are compared with the solutions reported in the literature and Abaqus finite element method. Finally, The influences of material constant k, boundary conditions, core-to-face sheets thickness ratio on the results are studied in detail.

---

In the present study, the frequency analysis of a smart sandwich plate is investigated using the finite element method. The sandwich plate is consisted of a magnetorheological elastomer (MRE) layer between two cross ply composite elastic faces. MRE is a smart material with controllable properties and a short time response when subjected to a magnetic field. This property can be used for improvement of the dynamic behavior of the structure. To model the sandwich plate with MRE layer, a complex shear modules is used to show the pre-‌yield behavior of MRE layer. In this study, effect of imperative parameters are discussed. In the present paper, the effect of different parameters such as applied magnetic field, the stacking sequences of the cross ply laminated faces in the sandwich plate and applying different boundary conditions on the natural frequencies and modal loss factors of the smart sandwich plate with MRE is investigated. The results show that considering special value for magnetic field, the stacking sequences of the composite layers of the sandwich plate and the boundary condition of the sandwich structure can lead to the satisfactory design of the sandwich plate.

---

This paper deals with the nonlinear transient vibration of composite sandwich plates with an electrorheological (ER) fluid core. The initial excitation is a distributed transverse load or the flutter instability due to supersonic airflow. The Bingham plastic model is adopted to accurately model the post-yield behavior of the ER material. . The first order piston theory is used for evaluating the aerodynamic forces. The von Karman strain-displacement relations are employed to account for moderately large deflection. The Hamilton’s principle is applied in conjunction with the finite element method to derive the equations of motion. The solution is then obtained through use the Newmark time integration scheme. Numerical investigations are conducted to study the effect of ER core layer on the vibration characteristics of the sandwich plate. The influence of the electric filed strength, ER core thickness, initial excitation and the boundary conditions on the settling time of transient vibration are also examined. The results show that the damping of transient vibration is significantly improved as the electric field applied to the ER layer, but the amplitude of post-flutter oscillations remains unchanged.

---

Today, composite material and sandwich plate structures are used more and more due to the unique properties such as a high ratio of strength to weight, corrosion resistance and energy or sound absorption ability. Corrugating sandwich structures is an effective method to reinforce mechanical properties of the composite materials. In this paper, dynamic analysis of these corrugated structures was carried out for a desired performance in the vibratory condition. One of the most important damages in the composite material layers is an inter-layer crack and also the separation between two layers. Vibration analysis of the trapezoidal corrugated sandwich plate was accomplished with ANSYS software using the finite element method. Simulated sandwich plate is a new model of corrugated sandwich plate which has a soft corrugated foam core and a cover of composite layers made from epoxy/glass. In order to validate the vibration behavior of the simulated sandwich plate, the results of experimental modal analysis were compared to the finite element method. The geometry and location effects of inter-layer crack on natural frequencies of the plate were investigated. It was found that with increasing crack dimensions the natural frequencies of the plate decreases and also depth of crack causes decreasing the natural frequencies which are promising results compared to the other references. The changes in vibration characteristics of the sandwich plate can produce comprehensive data to be used in training and designing of the artificial neural network for a promising approach in fault detection and prediction field.

---

The nonlinear vibration of sandwich viscoelastic plates under wide-band random excitation is investigated. The main attention is put on the influence of the one-to-one internal resonance, arisen from the close natural frequencies of the asymmetric modes of a near-square plate, on the response. The multi-modal response and the on-off intermittency phenomenon are especially considered. The mathematical modeling of the mid-layer is based on the moderate transverse shear strains and rotations, which have led to both geometrical and material nonlinearities. For the nonlinear constitutive equation of the mid layer, a single integral viscoelastic model is used. The displacement field in the thickness direction is also assumed to be linear for the in-plane components and quadratic for the out-of-plane components. Moreover, the Kirchhoff theory with the von-Karman nonlinearities are used for the outer layers. The solution is initiated by applying the perturbation method along with the Galerkin’s method to obtain integro-differential ordinary equations in time. These equations are then, solved using the Gaussian and non-Gaussian closure methods and the results are used to investigate the occurrence of the bifurcation with the aid of the Pseudo-arclength continuation method. Numerical results are presented for the multi-modal response and the minimum excitation intensity required for the nonlinear interaction between asymmetric modes.

---

Due to unique properties, lattice composite structure are used extensively in aviation, marine and automotive industry. In this research, experimental and numerical investigation of the free vibration of composite sandwich plates with triangular grid has been studied. For the fabrication of this plates, silicone mold, filament winding, and hand lay-up method were used. Stiffened plates and simple plates are fabricated, separately. Then, composite sandwich plates with triangular grid were created by attaching the two parts together. The modal test is done on the plates and natural frequencies have been extracted.The comparison of numerical and experimental results showed that there is a good agreement between them. By using Taguchi method, a parametric study was performed on the vibrational behavior of sandwich plates with triangular cores via three parameters that such as stiffeners’ number, stiffener thickness and skin thickness. The results show that the natural frequency of sandwich plates with triangular grid has a most sensitive to the stiffener thickness, and least sensitive to stiffeners’ number. The sensitivity of natural frequency is almost identical to stiffener thickness and skin thickness.To evaluate the efficiency of sandwich plates with triangular grid, the natural frequency of sandwich plates are compared with simple plates in the different boundary condition. The results show that the natural frequency of sandwich plates with the triangular grid is 133% and 138% higher than an equivalent simple shell at free and clamp boundary condition, respectively.

---

In this paper, the effect of shape memory alloy on low-velocity impact response of rectangular sandwich plates with composite facesheets and soft auxetic cores is investigated using a new higher-order global–local hyperbolic plate theory. In order to obtain accurate results with the least error, non-uniform and time-dependent distribution for the phases of SMA and the transverse compliance of the soft core are considered. Also, a refined contact law is proposed instead of using the traditional Hertz law and different contact laws are considered for the loading and unloading phases. Stiffness effects of all layers along with the effect of plate thickness on contact stiffness are considered. The obtained nonlinear finite element governing equations are solved by making use of an iterative algorithm at each time step. The results of the present study are compared with the experimental results in other references, and it is proved that the results are valid. Finally, the effect of auxetic core, core Poisson's ratio, SMA wires, and indenter energy on impact response of composite sandwich plat are investigated. The results show that the auxetic core increases the apparent stiffness of the contact area that causes an increase in impact forces and a decrease in the lateral deflection and impact duration. Besides, the SMA can absorb a remarkable portion of the stored impact-induced strain energy due to the superelastic and hysteretic natures of the SMA material, which results in increasing impact strength of the sandwich plate and decreasing the damage caused due to the impact.

---

In this research, the free vibration of a sandwich plate made of smart magnetostrictive face sheets and polymer composite core is studied. The effective elastic properties of carbon nanotube-reinforced composite are obtained by the rule of the mixture and micromechanical approach. A feedback control system follows the magnetization effect of Terfenol-D films on the vibration characteristics of a sandwich plate. Considering velocity feedback control gain value, the dimensionless frequency of sandwich plate can be changed to desired values due to magneto-mechanical coupling in magnetostrictive materials. The equations of motions are derived using Reddy’s third-order shear deformation theory, energy method, and Hamilton’s principle. The differential quadrature method (DQM) as a numerical method is used for calculating the vibration frequency of the sandwich plate. This numerical method presents the optimal results using weighting coefficients. The findings of this study show the effect of the vibration control system and geometrical properties of the composite sheet on vibration frequency of structures. These findings can be used in marine, aerospace, and civil industries.

---

---

In this research, the deformation of circular metal sandwich panels with vertical tube cores under blast load has been investigated numerically and experimentally. The relationship of energy balance in different components of the structure has been considered. The core tubes are installed in a cross arrangement and vertically with the same height between the upper and lower sheets of the sandwich structure. The amount of energy absorbed by the cores is determined according to their location in the structure and the effect of their number and diameter. The grouping of the desired tests for this research has been done according to the thickness of the sheet 1.2 and 2 mm and with aluminum cores with diameters of 12 and 16 (mm). Numerical simulation has been done in the form of free explosion and by defining the pressure function using the Conwep method in Abaqus software. To validate the numerical results, experimental tests have been carried out with the construction of sandwich structure. In both methods, the maximum lateral displacement of the structure at its center and the displacement in terms of distance from the center of the structure, at cores location have been measured. Increased number of tubes in the core of the structure decreased the maximum rise in the upper layer and decreased the transverse displacement of the lower sheet. Structures with fewer cores and less sheet thickness showed more energy absorption. The average difference between the results of numerical and experimental methods was approximately 11%.