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A new fourth-order in-plane displacement field based refined higher-order zigzag theory is proposed for analysis of laminated sandwich plate (for both skew and non-skew shaped) subjected to hygro-thermal conditions. In order to predict behavior of thick laminated sandwich plates, third-order transverse displacement field is taken. Zig-zag effects are introduced using linear unit Heaviside step function. The theory satisfies zeros transverse normal and shear stress condition at the bottom and top surface of the plate along with continuity condition at interface. The proposed model is free from any kind of C-1 or penalty function requirements. Nine-noded isoparametric finite element having twelve degrees of freedom per node is used during analysis. Since, the present theory incorporates transverse displacement field along with continuity conditions, is able to predict the behavior of thick sandwich plates more efficiently. In literature no results are present for skew laminated composite and sandwich plates therefore, present results for skew plates are entirely new and will serve as benchmark for future studies. [ABSTRACT FROM AUTHOR]

A new simple "four-variable shear deformation" plate model is proposed in this work to demonstrate the hygro-thermal environment effects on dynamic and buckling of functionally graded material "sandwich plates" supported by "Winkler–Pasternak" elastic foundations. Equations of motion are obtained from Hamilton's principle containing the hygro-thermal influences. This model uses only "four variables" and considers trigonometric variation of "transverse shear stress." In addition, these stresses become zero at the upper and lower surfaces of the "sandwich plate." The novelty of this formulation is the addition of the integral term in the field of displacement, which leads to a reduction of the number of unknowns and basic equations. Various kinds of functionally graded material "sandwich plates" are examined in this study. To verify the validity of the model, the calculated results are compared with the existing results. Comparison investigations reveal that the computed results of the proposed formulation are in excellent agreement with those of other "higher shear deformation theories." Parametric investigation is established to demonstrate the effects of temperature rise, moisture condition, elastic foundation coefficients, and power law index on the vibration and buckling of functionally graded material "sandwich plates." [ABSTRACT FROM AUTHOR]

This study aims to produce sandwich-structured composite boards with flame retardance, far-infrared emissivity, and electromagnetic shielding effectiveness using nonwoven, weaving processes, and heat treatment. Needle punching and roller-type hot pressing are used to improve their tensile strength, tensile elongation, puncture strength, and burst strength. The limiting oxygen index is 30 regardless of whether the flame retardance/far-infrared emissivity/electromagnetic shielding effectiveness composite board is stainless steel (SS), SS+Ni–Cu (nickel-coated copper), or SS+Ni–Cu+Cu (copper) composite fabrics. SS+Ni–Cu and SS+Ni–Cu+Cu composite boards both have optimal thermal conductivity at the eighth test hour. SS–B composite board exhibit far-infrared emissivity of 0.81; moreover, they have optimal electromagnetic shielding effectiveness of −41dB at 2450 MHz when they are laminated into three layers at a 90° lamination. [ABSTRACT FROM AUTHOR]

In this study, non-linear low-velocity impact response of a simply supported sandwich plate with CNTRC face sheets subjected to the impactors with different geometrical shapes is investigated. It has been assumed that the sandwich plate is made up of two face sheets reinforced with CNTs graded along their thickness as X profile and a homogeneous core. In CNT-reinforced layers, a micromechanical model has been used to obtain the effective material properties and the analysis is performed in the framework of the Reddy's higher order shear deformation theory with regard to thermal effects. An analytical model is proposed to capture the response performance of the three-layer sandwich plates under different thermal environments. Through the proposed analytical study, in order to characterize the contact force between the sandwich plate and the impactors, the modified Hertz contact law is utilized. Rayleigh-Ritz method is applied to the Hamilton principle in order to find the set of equations of motion for the impactor as well as the CNTRC sandwich plate. Afterwards, the solution in the time domain is obtained based on Newmark's numerical time integration scheme. After validating the proposed approach, in order to examine the influences of various involved parameters, different parametric studies are conducted. It has been demonstrated that the variation of the initial kinetic energy as one of the parameters under study has a significant effect on the central displacement, contact force, and indentation in both conical and cylindrical impactors and the change in the radius of the cylinder has an insignificant effect on the central displacement. As well, in the case of equal masses, the cylindrical impactor causes more amount of indentation with respect to conical. [ABSTRACT FROM AUTHOR]

The boundary layer hygrothermal stresses in the thick sandwich cylinder with laminated face are investigated. Uniform and through the thickness steady-state distribution for temperature and moisture content can be considered in the analysis. A displacement based layer-wise formulation is presented for analysis of thick sandwich composite cylinders subjected to hygrothermal loading conditions. Considering a general displacement field and employing a displacement based layer-wise theory, the governing equations of thick laminated sandwich cylinder are obtained. The displacement based formulation is derived for thick sandwich cylinder, which is subjected to non-uniform hygrothermal loading conditions. The faces of the sandwich cylinder are made of laminated composite with general layer stacking. The governing equations of the system include a set of coupled differential equations on the displacement components of the numerical surfaces. A semi-analytical solution is developed and the governing equations are solved for free edge boundary conditions. The accuracy of the numerical results is validated by the results of the finite element simulation and good agreements are seen between the predicted results. The free edge interlaminar stresses distributions are presented for thin and thick sandwich composite cylinders for uniform and non-uniform loading conditions. It is concluded that the presented layer-wise formulation is efficient and accurate method for analysis of thermal and hygroscopic stresses in thick and thin sandwich cylinders with general layer stacking. [ABSTRACT FROM AUTHOR]

In this article, the geometrical nonlinear free vibration behaviour of shear deformable laminated composite single/doubly curved shell panel in hygrothermal environment is investigated. A general nonlinear mathematical model of laminated composite doubly curved shallow shell panel has been developed based on the higher order shear deformation theory and Green-Lagrange geometric nonlinear kinematics. All the nonlinear higher order terms have been included in the present mathematical model to achieve a realistic case. In addition to that, the composite material properties are considered as temperature and moisture dependent through hygro-thermo-elastic constitutive relations. The governing equation of laminated composite curved panel is obtained using Hamilton’s principle and discretised using nonlinear finite element steps. The desired responses are computed numerically using a direct iterative method. The convergence behaviour of present numerical model has been checked and validated by comparing the responses with those available published results. The effect of different geometrical and/or material parameters on nonlinear vibration behaviour of laminated composite doubly curved shell panel under hygrothermal environment is computed and discussed in detail. [ABSTRACT FROM AUTHOR]

Refined two-dimensional models are proposed for the static hygrothermoleastic analysis of multilayered composite and sandwich shells. These shell models are developed in the framework of the Carrera's unified formulation (in a general and unified manner) by considering both equivalent single layer and layerwise multilayer description. The principle of virtual displacements contains elastic, thermal and hygroscopic strains. The governing equations allow mechanical, thermal and hygroscopic loads to be applied and they are solved in a closed-form solution. Thermal and hygroscopic loads are defined by means of appropriate temperature and moisture content profiles through the thickness of the shell, such profiles can ‘a priori’ be assumed or they can be calculated by solving the Fourier heat conduction equation and the Fick's moisture diffusion law. Such equations are solved in steady-state conditions and in curvilinear coordinates for the shell geometries. The presence of loads due to hygroscopic and thermal effects (in addition to the mechanical load) modifies the bending response of multilayered shells. Comparisons between classical and refined models, and between assumed and calculated temperature and moisture content profiles are proposed in the cases of composite and sandwich shells. The use of refined models combined with calculated temperature and moisture content profiles through the thickness is mandatory for a correct elasto-thermo-hygroscopic analysis of multilayered structures. [ABSTRACT FROM AUTHOR]