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The present study investigates the global buckling behavior of sandwich beams with graded lattice cores. The continuous equivalent theory is utilized to construct a discrete graded lattice core sandwich beam for a continuously varying gradient beam, whose material properties vary with position. A theoretical model of sandwich beams with graded lattice cores is established using the energy method. Finite element models are developed in ABAQUS to validate the theoretical results. Furthermore, four sets of specimens were manufactured and tested to validate the theoretical analysis methods used. The effects of the graded parameters and geometric parameters on the critical buckling load of sandwich beams with graded lattice cores are discussed. The graded lattice sandwich beams exhibit global buckling when the graded parameter is small, with the influence on buckling performance being minor. However, as the graded parameter increases, the graded lattice sandwich beams experience local buckling, and their buckling resistance weakens. Therefore, graded parameters that are too large and cause local buckling should be avoided in gradient design. [ABSTRACT FROM AUTHOR]

In this paper the vibration correlation technique (VCT) has been used as a nondestructive method for predicting the buckling load of the composite lattice-core sandwich conical shells. This technique is capable of predicting the buckling load of different structures without reaching the failure point through modal testing. The composite lattice-core sandwich conical shell has been fabricated using a filament winding process. To perform the expriment, the fundamental natural frequency of the specimen is measured under stepped axial compression loading. The procedure is followed up without actually reaching the instability point when the structure collapses and is no longer usable. A finite element model has also been built in ABAQUS in order to determine the correlation between natural frequency and applied compressive load. A comparison of the results indicated that the VCT has provided a reliable estimate of the buckling load of composite lattice-core sandwich conical shells, especially when the structure is loaded up to at least 66% of the experimental buckling load and accuracy of the VCT decreases when the maximum load is lower than 43% of the buckling load. Results also revealed that the linear fitted curve is unsuitable for the correlation between frequency of vibration and applied load in order to predict buckling load. [ABSTRACT FROM AUTHOR]

In this paper, theoretical analysis, numerical simulation and mechanical test on the 3D printed lattice sandwich structures are carried out to study the buckling performance. 2 types of lattice structures, body centered cubic (BCC) and rhombic dodecahedron (DOD) are included. The lattice sandwich panels are made of ALSi10 Mg alloy materials and manufactured using the selective laser melting technique. The comparative results show that DOD lattice sandwich panel not only has higher bearing capacity, but also shows stronger toughness in the post-buckling stage than BCC type panel, even they have the same characteristic size. The buckling mode depends on the topology of the unit cell. For BCC and DOD type panels, the main buckling modes are local buckling and global buckling respectively. The reasons of different buckling modes are discussed. Moreover, the buckling evolution and failure modes of the two types of panels in the post-buckling stage are investigated. [ABSTRACT FROM AUTHOR]

Sandwich structures with an asymmetric configuration are employed to introduce in-plane loads as well as to connect them with other structural components. Understanding their failure mechanism is crucial to ensure the safety design of aircraft. This paper investigates experimentally and numerically the mechanical behavior of asymmetric sandwich panels (ASPs) under compression. Quasi-static tests are conducted to obtain the buckling loads, post-buckling behavior, and load-bearing capacity of ASPs. A non-linear finite element (FE) model is developed to elucidate their damage behavior and failure mechanism. Numerical predictions are compared with test results to validate the FE model and failure analysis. The results demonstrate that the presence of a tapered region significantly influences stress distribution and failure initiations. A parametric study is also conducted to investigate the effects of the tapered angle on the compression response of ASPs. The reported results can provide a reference for the optimal design of ASPs. [ABSTRACT FROM AUTHOR]

Previous studies on the thermal buckling of sandwich plates with composite face sheets indicate that only thin skins with high stiffness and low coefficients of thermal expansion (CTE) can lead to the desired buckling temperatures. Thus, carbon nanotubes (CNTs) that can significantly enhance thermo-mechanical properties of fibre-reinforced polymer composites are used in the present study to increase the critical buckling temperature of sandwich plates with soft core and laminated composite face sheets. First, a comprehensive series of experimental tests are conducted to evaluate the effects of nanotubes on thermo-mechanical properties of the face sheets. The experimental results indicate that using only 0.3% CNTs considerably increases the longitudinal and transverse Young's modulus and shear modulus of the carbon fibre/epoxy composite face sheets. The obtained data also show that CNTs significantly decrease the CTE of composite skins. Subsequently, thermal buckling equations of sandwich plates with CNT-reinforced composite face sheets are derived based on piecewise low-order shear deformation theory (PLSDT). Three analytical, semi analytical, and numerical methods are used to investigate thermal buckling behaviour of the sandwich plates with various boundary conditions. To verify the results, several comparisons are performed, which show that the implemented methods can predict the buckling temperatures of sandwich plates with high accuracy. Finally, a parametric study is conducted to examine the effects of CNTs on the thermal buckling of sandwich plates for different length to thickness ratios, thicknesses of face sheets, stacking sequences of layers, and various types of boundary conditions. The results indicate that CNTs can increase the critical buckling temperature of sandwich plates by 22%–36%, based on the layup, geometrical parameters, and boundary conditions. [ABSTRACT FROM AUTHOR]

The nonlinear buckling and post-buckling response of imperfect porous plates is investigated analytically in this paper. The porous materials with elastic moduli are assumed to vary through the thickness of the plate according to two different distribution types. Governing equations are derived based on the classical shell theory taking into account Von Karman nonlinearity and initial geometrical imperfection. Explicit relations of load–deflection curves for rectangular porous plates are determined by applying stress function and Galerkin's method. The accuracy of present theoretical formulation is verified by comparing it with available results in the literature. The effects of varying porosity distribution, porosity coefficient, boundary condition and imperfection on post-buckling behavior of the porous plate are studied in detail. A parametric study is carried out to investigate the effects of varying porosity distribution, porosity coefficient, boundary condition and imperfection on post-buckling behavior of the porous plate. The results show that the critical buckling loads decrease with increasing porosity coefficient and the post-buckling curves for nonlinear symmetric porosity distribution are always higher than those for nonlinear non-symmetric porosity. [ABSTRACT FROM AUTHOR]

Modeling a periodic structure as a homogeneous continuum allows for an effective structural analysis. This approach represents a sandwich panel as a two-dimensional plate of equivalent stiffness. Known as the equivalent single-layer, the method is used here to analyze bifurcation buckling of three types of sandwich panels with unidirectional stiffeners in the core: truss-core, web-core and corrugated-core panels made of an isotropic material. The transverse shear stiffnesses of these panels can differ by several orders of magnitude, which cause incorrect buckling analysis when using the equivalent single-layer model with the first-order shear deformation theory. Analytical solution of the problem predicts critical buckling loads that feature infinite number of half-waves in the direction perpendicular to the stiffeners. Finite element model also predicts buckling modes that have non-physical, saw-tooth shape with infinite curvature at nodes. However, such unrealistic behavior is not observed when using detailed three-dimensional finite element models. The error in the prediction of the critical buckling load is up to 85% for the cases considered here. The correction of the equivalent single-layer model is proposed by modeling the thick-faces effect to ensure finite curvature. This is performed in the finite element setting by introducing an additional plate with tied deflections to the equivalent single-layer plate. The extra plate is represented with bending and transverse shear stiffness of the face plates. As a result, global buckling is predicted accurately. Guidelines are proposed to identify the sandwich panels where ordinary model is incorrect. Truss-core and web-core sandwich panels need the correction. Corrugated-core panels without a gap between plates in the core have smaller shear orthotropy and do not need the correction. Modeling the thick-faces effect ensures correct results for all cases considered in this study, and thus one should resort to this approach in case of uncertainty whether the ordinary equivalent single-layer model is valid. [ABSTRACT FROM AUTHOR]

In this manuscript, buckling of carbon nanotubes reinforced circular cylindrical composite shell under hydrostatic presser with its ends closed by rigid disks is investigated, using Fourier decomposition and the Galerkin method. The accuracy of the utilized method is verified with previous research in buckling behavior of circular cylindrical shells. Both types of functionally graded and uniform distribution patterns of carbon nanotubes are studied. The novelty of this study is investigating the influence of carbon nanotubes distribution type and volume fraction on buckling resistance of carbon nanotubes reinforced circular cylindrical composite shell. Furthermore, the effect of material type and volume fraction of metal layers on fiber metal laminates is illustrated. The results show that buckling resistance of composite cylindrical shells increase about 10% by reinforcing with 5% carbon nanotubes. Also, it is shown that metal types Az91 and Ti6AlV have about same effect on buckling resistance of fiber metal laminates cylinders, and their effect are about 15% more than the effect of Al2024. With exploiting the executed analysis, pipes with optimum buckling resistance to weight ratio can be designed for hydrostatic loading. [ABSTRACT FROM AUTHOR]

The non-linear hygrothermal and mechanical buckling responses of FG sandwich plates resting on two-parameter elastic foundations are presented in this study. Non-linear Fourier temperature distribution is considered as a special case. A hyperbolic displacement model is proposed in the present investigation. The present model involves four unknown variables, and the shear stresses on the bottom and top of the plate surfaces are equal to zero. The effective material properties of the FG sandwich face sheets are presumed to be varied in the direction of the thickness using a simple power law distribution, while the core is supposed to be purely ceramic. The stability equations are deduced by the principle of virtual work, containing the effect of foundations interaction and hygrothermal effects based on the present model. The hygrothermal effects are considered as non-linear, linear and uniform distribution through the plate thickness. Comparison examples are presented to verify the accuracy of the present model. The effects played by the temperature rise, moisture concentration, parameters of elastic foundation, side-to-thickness ratio, aspect ratio of the plate, the inhomogeneity parameter on the critical buckling of FG sandwich plates are investigated. [ABSTRACT FROM AUTHOR]

This article presents a theoretical formulation presented for conducting a buckling analysis of the composite sandwich plate with multiple holes via the homogenization method. The validity of the theoretical formulation was verified by comparing the results of the finite element analysis and experimental analysis. Finally, the theoretical formulation was used to optimize a composite sandwich plate with multiple holes for the design of an aircraft structure to minimize the mass. The optimization result allows a database to be obtained on the buckling characteristics of composite sandwich structures with multiple holes for applying aerospace applications. We then concluded that the theoretical formulation is well-suited to buckling analysis of a composite sandwich structure with multiple holes for aerospace applications due to their relative simplicity and computational efficiency. [ABSTRACT FROM AUTHOR]

The integration of inserts into sandwich panel constructions is a complex multi-step process with significant human intervention that also limits the geometrical freedom of the insert design. In a standard sandwich construction, the panel core is made up of multiple materials across its main components: insert, potting and core. This multi-material assembly is not only difficult to manufacture, but it also promotes stress jumps at the insert-core interface, leading to a sub-optimal load distribution from the bolt to the panel core. Additive manufacturing (AM) can lead to a single-part core and insert assembly with more optimised insert geometries that can better transmit the loads applied to the panel. Previous work by the authors has explored the manufacturing limits and the failure modes of AM inserts integrated in cores printed out of sintered AlSi10Mg. The conclusions were that the core walls and insert elements should have a minimum design thickness of 0.5 mm to survive the tapping process without facesheets attached and it was found that the main failure mode of the geometries tested in pull-out was buckling of the insert walls. Based on these results, the paper proposes a novel insert design philosophy that can delay the buckling of 3D printed inserts and move the failure point of the insert away from the bolt. A set of inserts that follow this design direction is manufactured and tested under normal pull-out loads and the optimised designs outperform standard printed insert geometries by a factor of three. The design philosophy can be further developed to offer a suitable alternative to the current insert standard. [ABSTRACT FROM AUTHOR]

An analytical investigation on buckling and postbuckling behavior of sandwich cylindrical shells comprising functionally graded material layers and subjected to uniform temperature rise and external pressure in thermal environments is presented in this paper. Two sandwich models corresponding to functionally graded material face sheets and core layer are considered. The properties of constitutive materials are assumed to be temperature dependent and effective properties of functionally graded material are determined according to linear rule of mixture. Formulations are based on the classical shell theory taking Von Karman–Donnell nonlinearity and elastic constraint at edges into consideration. Multi-term solutions of deflection and stress function are assumed to satisfy simply supported boundary conditions and Galerkin method is applied to derive nonlinear load–deflection relations from which buckling loads and postbuckling paths are determined. The effects of sandwich configurations, material gradation, tangential constraints of edges, and temperature dependence of material properties on buckling loads and postbuckling curves are analyzed through numerical examples. [ABSTRACT FROM AUTHOR]

In this work, biaxial buckling analysis of sandwich plates with symmetric composite laminated core and two functionally graded nanocomposite face sheets is carried out by a new improved high-order theory. The nanocomposite face sheets are carbon nanotube (CNT)-reinforced nanocomposites and the material properties of the nanocomposites plates are graded along the thickness and are estimated though the Mori–Tanaka approach. CNTs are assumed randomly oriented and aggregated into some clusters. The same third order theory is used for modeling of core and the faces sheets. The theory has third and second orders of z for in-plane and normal displacements, respectively. The principle of minimum potential energy is used to derive the equations of motion and boundary conditions. Analytical solution for static analysis of simply supported sandwich plates under biaxial in-plane compressive loads is presented using Navier’s solution. The effects of CNT volume fraction, CNT aggregation states, CNT distribution, biaxial loads ratio, and geometric dimensions of sandwich plate are investigated on the overall buckling of functionally graded carbon nanotube-reinforced nanocomposite sandwich plates. [ABSTRACT FROM AUTHOR]

Analytical solution of the buckling problem for a composite cylindrical sandwich panel subjected to axial load is presented in the paper. The straight longitudinal edges of the panel are fully clamped, and the curved sides are simply supported. This loading results in the biaxial compression of the panel. The buckling analysis is performed using the equations of the engineering theory of laminated cylindrical shells, taking into account the transverse shear deformations. The system of linearized buckling equations is derived in terms of unknown displacements, deflection, and angles of rotation of the normal to the middle surface of the panel. The equations are solved by combining the Levy and Galerkin methods. In this approach, the deformed panel was approximated by trigonometry and beam functions. The analytical formula for the critical load has been derived and verified using finite-element analysis. Based on this formula, the influence of Poisson's effect on the value of buckling load has been studied. Design application of the formula is demonstrated for a specified value of the critical load. [ABSTRACT FROM AUTHOR]

The present paper is concerned with the active control of thermal buckling and vibration of a sandwich composite laminated plate with piezoelectric fiber-reinforced composite actuator facesheets in a thermal environment. An active temperature feedback control strategy is proposed for the thermal buckling of the composite sandwich plate. The results of numerical simulations show that the piezoelectric actuator can significantly improve the thermal buckling characteristics of the composite plates. The influence of the active thermal buckling control gain on the damping ratio and natural frequency of the structure is also investigated. From the numerical results it is observed that the active thermal buckling control with temperature feedback gain can not only enlarge the critical buckling temperature but can also reduce the resonant amplitude of the structure. Furthermore, the optimization problem is studied and it is found that the critical buckling temperature can be optimized by varying the fiber orientation in the piezoelectric fiber-reinforced composite layer. The active thermal buckling control method presented in this paper working in combination with the vibration control strategy can significantly improve the stability of the laminated composite plates. The present study will be useful for designing laminated composite structures used in the thermal environment. [ABSTRACT FROM AUTHOR]

In this paper, higher order closed-formed analytical solutions for the buckling analysis of functionally graded sandwich rectangular plates are obtained using a unified shear deformation theory. Three-layered sandwich plates with functionally graded skins on top and bottom; and isotropic core in the middle are considered for the study. The material properties of skins are varied through the thickness according to the power-law distribution. Two types of sandwich plates (hardcore and softcore) are considered for the detail numerical study. A unified shear deformation theory developed in the present study uses polynomial and non-polynomial-type shape functions in terms of thickness coordinate to account for the effect of shear deformation. In the present theory, the in-plane displacements consider the combined effect of bending rotation and shear rotation. The parabolic shear deformation theory of Reddy and the first-order shear deformation theory of Mindlin are the particular cases of the present unified formulation. The governing differential equations are evaluated from the principle of virtual work. Closed-formed analytical solutions are obtained by using the Navier's technique. The non-dimensional critical buckling load factors are obtained for various power-law coefficients, aspect ratios and skin-core-skin thickness ratios. [ABSTRACT FROM AUTHOR]

In this study, the nonlinear buckling and post-buckling analysis of stiffened truncated conical sandwich shells with functionally graded face sheets and a functionally graded porous core resting on the Winkler–Pasternak elastic foundation subject to a uniform axial compressive load has been investigated. Shells are reinforced by functionally graded material stringers and rings, in which the change of spacing between stringers in the meridional direction also is taken into account. The stability equations of the shell are derived based on the first-order shear deformation theory with a von Karman–Donnell type of kinematic nonlinearity and the smeared stiffener technique. Those equations are solved by the Galerkin method to determine the effects of stiffeners, shell characteristics, material properties, porosity coefficient, and elastic foundation on the critical buckling load and for analyzing the post-buckling load–deflection curves. The approaches are verified with the known results in the literature. [ABSTRACT FROM AUTHOR]

Honeycomb sandwich panels are widely used in marine, aerospace, automotive and shipbuilding industries. High strength to weight and excellent energy absorption are features that make these structures unique. Foam filling the honeycomb core enhances the mechanical properties of sandwich panels considerably. In the present study, the buckling behavior of Nomex honeycomb core/glass-epoxy face sheet sandwich panel for both bare and foam-filled honeycomb core is investigated numerically and experimentally, considering the viscoelastic properties of the sandwich panel. Indeed, the viscoelastic properties of the composite face sheet and foam are determined by relaxation test and are implemented in ABAQUS using VUmat code. The finite element method is also performed using ABAQUS to model the buckling behavior of the sandwich panel incorporating both elastic and viscoelastic material behaviour. The effects of composite face sheet lay-up, core thickness, core cell size, and foam filling are also evaluated. The experimental and numerical results show that the foam increases the critical buckling load and energy absorption. [ABSTRACT FROM AUTHOR]

Bending and buckling analyses of heterogeneous annular/circular micro sandwich plate which is located on Pasternak substrate is presented in the current study. The plate's core is made of saturated porous materials and face sheets are made of functionally graded piezo-electro-magnetic polymeric nano-composites. The displacement components of the plate described based on FSDT and MCST is employed to analyze the structure in micro scale. Length scale parameter of MCST shows the difference between macro and micro scales elasticity theory. Material properties of the three layers are varied across the thickness following different patterns and in addition, are temperature-dependent. The face sheets are subjected to electro-magnetic fields and pre loads. Using energy method and variational calculus, the equations are obtained and solved via GDQ as a numerical method for various boundary conditions. To examine the reliability of the results, they are compared with previous studies and verified. Effect of different properties and aspect ratio of the plate are investigated and highlighted. The results depicted by enhancing the porosity, the critical buckling load and maximum transverse deflection decreases and increases, respectively. Also increasing temperature leads the buckling load to more values and vice versa about deflection of the plate. The findings of this research can help to design and create more efficient structures especially smart one as sensors or actuators. [ABSTRACT FROM AUTHOR]

Buckling and crushing behavior of foam-core hybrid composite sandwich columns under edgewise compressive load is dealt in this study. Composite laminates with different stacking sequence configurations made of glass and Dyneema-woven fabrics and AL 2024-T3 sheets were used in combination of polyvinyl chloride foam core to manufacture the specimens. Effects of face sheet thickness and stacking sequence configuration, slenderness ratio, boundary conditions, and sandwich reinforcement with through-thickness resin pins on the buckling and crushing behavior of the specimens were investigated. The results revealed that using the resin pins changes the unstable Euler buckling mode to a more stable progressive end-crushing and significantly increases the buckling load, specific buckling load, and energy absorption capability, which are highly favorable. Also, the results showed that in the specimens with fiber metal laminates, the major failure modes are face sheet-core debonding and face sheet delamination. However, based on the results, specimen with hybrid face sheets made from Dyneema fabrics and aluminum plates has the highest buckling load as well as the highest specific buckling load. Also, a specific fixture was designed to laterally clamp the sandwich column which causes a reduction in the probability of specimen end-crushing and significantly increases the buckling load. [ABSTRACT FROM AUTHOR]

In this paper, the free vibration and buckling analyses of the cylindrical sandwich panel with magneto-rheological fluid layer for simply supported boundary conditions was performed based on an improved higher order sandwich panel theory. This paper deals with investigation of the effects of magnetic field, geometrical parameters such as the core thickness to the panel thickness ratio, MR layer thickness to the panel thickness ratio and the fiber angle on the natural frequencies, loss factors and buckling loads corresponding to the first four mode shapes. In order to validate the results obtained from the present study, the cylindrical sandwich panel was simulated and analyzed in finite element software ABAQUS. A good agreement was observed between the results of present method and those extracted from simulation. [ABSTRACT FROM AUTHOR]

The nonlinear torsional buckling and post-buckling of ceramic functionally graded material (C-FGM-M) stiffened cylindrical shell surrounded by Pasternak elastic foundation in thermal environment are investigated in this paper. The C-FGM-M cylindrical shell is reinforced by ring and stringer stiffeners system in which the material properties of shell are assumed to be continuously graded in the thickness direction. Based on the classical shell theory, theoretical formulations are derived with the geometrical nonlinearity in von Karman sense and the smeared stiffeners technique. The three-term approximate solution of deflection is chosen more correctly and the explicit expression for finding critical load and post-buckling torsional load–deflection curves are given. The effects of geometrical parameters, temperature, stiffeners and elastic foundation are investigated. [ABSTRACT FROM AUTHOR]

In this work, a first-order discrete layer model is performed to deal with the free vibration and buckling analysis of composite sandwich plates in thermal environment. Owing to considering the effect of rotary inertias and shear deformation, thin-to-moderately thick shells can be analyzed. The differential equations of motion are derived from Hamilton's principle, and account for the nonlinear variation of the in-plane and transverse displacements through the thickness due to temperature variation. These equations are solved by means of the closed-form Navier method, and validated by comparing the numerical results obtained by the present method with the findings published in literatures. Finally, the variation tendency of critical buckling temperature with material parameters is evaluated and shown graphically. [ABSTRACT FROM AUTHOR]

The governing equations for the buckling of honeycomb cores with various cell geometries under combined compression and shear are established and three types of core including rectangular, hexagonal and triangular cores are under consideration. After invoking the Bloch wave representation form, the equations are simplified by the periodicity and the hypothesis that the out-of-plane displacement remains zero at the intersections. Different cell geometries and load cases are taken into account and numerical results offer validation for the analytical solutions. Moreover, the results of Finite Element (FE) models show that the fine results can only be acquired by models with appropriate cell numbers. Experimental study is conducted on the regular hexagonal honeycomb structures. Both the results of the numerical benchmarks and the experiments prove the effectiveness of the proposed analytical method and the hypothesis for predicting the buckling load of honeycomb structures. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to study the effect of porosity on vibration and buckling responses for sandwich plate supported with different boundary conditions at the edges. The formulation is performed for recently developed sandwich plate using new modified sigmoid function based functionally graded material plate of different symmetric and asymmetric configurations. Three different types of porosity are considered viz. even, uneven but symmetric, and uneven but non-symmetric. A new uneven non-symmetric porosity model is used in which micro-voids are varied in accordance with material property variation in the thickness direction in order to capture the accurate distribution of voids on the plate. The variational principle is employed to derive equilibrium equations. A closed form solution is obtained using the assumed solution with shape functions satisfying the edge boundary conditions using Galerkin Vlasov 's method. Free vibration and buckling analysis have been performed to study the effect of porosity, geometric configurations, inhomogeneity parameter, and buckling load parameter. These studies are performed on sandwich sigmoid function based functionally graded material plate for different boundary conditions and plate configurations. It is observed that in several cases with uneven symmetric porosity (P-2) distribution, the reduction in effective inertia appears to be more prominent in comparison to the reduction in effective stiffness of the plate and uneven non-symmetric porosity (P-3) distribution ascertains the realistic idealization for a plate with micro-voids. The higher modes of vibrations and nature of in-plane load are very sensitive to the type of porosity distribution considered. In addition, zero frequency parameter and zero critical buckling load in a load frequency curves correspond to critical buckling load and frequency parameter, respectively. The accuracy and validation of the present formulation are determined by considering different examples. [ABSTRACT FROM AUTHOR]

This paper presents an analytical solution for vibration and buckling of functionally graded (FG) sandwich beams using various quasi-3D theories, which consider effects of both shear and normal deformation. Sandwich beams with FG skins–homogeneous core and homogeneous skins–FG core are considered. By using the Hamilton’s principle, governing equations of motion are derived. An analytical solution is presented, and the obtained results by various quasi-3D theories are compared with each other and with the available solutions in the literature. The effects of normal strain, power-law indexes, skin–core–skin thickness and slenderness ratios on vibration and buckling behaviour of sandwich beams are investigated. [ABSTRACT FROM AUTHOR]

Mechanical stability of the functionally graded rectangular plates bonded with functionally graded piezoelectric layers is studied in the present research. Classical plate theory is employed in the description of three components of the plate displacement. Geometric nonlinearity is considered in the strain–displacement relations using the von Karman equation. The constitutive relations are developed for the functionally graded material core and functionally graded plate material layers in the general state. The top and bottom of the piezoelectric layers is assumed to be short-circuited. Three equilibrium equations as well as Maxwell equation are constituted of four governing differential equations of the problem. Some important nondimensional parameters representing the geometries of the sandwich plate incorporated with nonhomogeneous index of the material properties are considered for this analysis. The results indicate that these parameters have important effects on the buckling loads. [ABSTRACT FROM AUTHOR]

This paper presents a new higher-order shear deformation theory for static, buckling and free vibration analysis of functionally graded sandwich beams. In this theory, the axial displacement accounts for a third-order and inverse trigonometric distribution, and the transverse shear stress satisfies the traction-free boundary conditions on the top and bottom surfaces of the beams. Governing equations of motion are derived from the Hamilton’s principle for sandwich beams with homogeneous hardcore and softcore. Navier-type solution for simply-supported beams is developed to solve the problem. Numerical results are obtained to investigate effects of the power-law index, span-to-height ratio and thickness ratio of layers on the displacements, stresses, critical buckling load and frequencies. [ABSTRACT FROM AUTHOR]

In this paper, a new analytical approach is developed for buckling of composite sandwich pipes with iso-grid core under uniform external lateral pressure. Firstly, the stiffness contributions of iso-grid cores are evaluated through the new force and moment effect analysis. Then, iso-grid core is transformed into a solid pipe, as the middle layer of the sandwich pipe. The outer, inner, and middle pipes are transformed into an equivalent single-walled pipe. Therefore, composite sandwich pipe with iso-grid core is equalized with a single-walled pipe of the same stiffness. The Rayleigh–Ritz energy method is used to calculate the critical buckling pressure of the composite sandwich pipes with iso-grid cores. The efficiency and accuracy of the presented approach are confirmed by comparing the analytical solutions with finite element results obtained from ABAQUS and other works, showing a good agreement with each other. A parametric study is then carried out to investigate the effect of the scale of the structure, outer and inner pipes ply stacking sequence, radius to total thickness ratio, stiffener to outer and inner pipe thicknesses ratio, and stiffener angle on the buckling of sandwich pipes. Finally, applications of the present approach were demonstrated for designing of tending toward constant various structural applications such as offshore pipelines. [ABSTRACT FROM AUTHOR]

In piezoelectric materials and at the nano-scale, there is a coupling between electrical polarization and strain gradients fields, which is called flexoelectricity. The effects of this phenomenon seem to be negligible in micro/macro scales. The current study has attempted to have a cohesive concentration on the buckling behaviors of sandwich plates. To achieve the abovementioned aim with a higher accuracy, the flexoelectric effect assumes to be existing on the top and bottom face sheets and the core is a composite plate. Also, based on statistics, the first-order shear deformation theory seems to lead to more accurate results. Therefore, in the present research we follow this method to obtain results. The analytical method is applied to solve higher order governing equations. In addition, the critical buckling voltage is calculated considering the flexoelectricity, and it is found that the effects of flexoelectricity play significant roles in determining the critical buckling voltage. Moreover, it is revealed that the thickness of the flexoelectric face sheets and the aspect ratio of the sandwich plate play the same role in critical buckling load variations. It means that the critical buckling load decreases when the thickness of the flexoelectric face sheets or the aspect ratio of the sandwich plate increases and vice versa. The results of the present work can be used for the optimum design and control of similar systems such as micro-electro-mechanical and nano-electromechanical devices. [ABSTRACT FROM AUTHOR]

This paper presents new results of static bending in high temperature and thermal buckling of sandwich functionally graded beam based on new third-order shear deformation theory (TSDT) and finite element formulations. We assume that the sandwich beam placed in a high-temperature environment for a long time, and so that the temperature distributions uniformly across the beam thickness and material properties are temperature-dependent. Using this TSDT, the analysis does not need any shear correction factors and has no shear-locking. The results show that not all functionally graded structures could process similar to mechanical behaviors and have the ability to perform in high temperature. [ABSTRACT FROM AUTHOR]

The main objective of this article is to analyze the buckling of sandwich annular plates with carbon nanotube-reinforced face sheets subjected to in-plane mechanical loading resting on the elastic foundation. It is assumed that the sandwich plate is composed of the homogeneous core layer and two functionally graded carbon nanotube-reinforced composite face sheets. The effective material properties of the functionally graded carbon nanotube-reinforced composite face sheets are estimated using the modified rule of mixture method. The higher-order shear deformation theory along with the variational differential quadrature method is employed to derive the governing equations. To this end, the quadratic form of energy functional of the structure is derived based on higher-order shear deformation theory which is directly discretized using numerical differential and integral operators. The validity of the proposed numerical approach is first shown and the effects of various parameters are then investigated on the buckling of sandwich annular plates. It was found that the elastic foundation coefficients, type of distribution of carbon nanotubes, inner-to-outer radius ratio and core-to-face sheet thickness ratio play important roles in the stability of the structure. Furthermore, the numerical results of the higher- and first-order shear deformation theories are compared. [ABSTRACT FROM AUTHOR]

Optimization of embedded piezoelectric sandwich nanocomposite plates for dynamic buckling analysis is presented in this work based on Grey Wolf algorithm. The Grey Wolf algorithm mimics the leadership hierarchy and hunting mechanism of grey wolves in nature. In addition, the main steps of hunting, searching for prey, encircling prey, and attacking prey are employed. The structure is composed of a laminated functionally graded-carbon nanotubes reinforced layers as core integrated with sensor and actuator layers considering structural damping effects. Two-dimensional magnetic and 3D electric fields are applied to core and piezoelectric layers, respectively. Sinusoidal shear deformation theory is utilized for obtaining the motion equations and differential quadrature method is applied for solution. Also, a proportional-derivative controller is employed to control the dynamic behavior of the structure. Finally, the optimum designs for the structure are evaluated using proposed Grey Wolf algorithm based on the geometrical parameters of plate, applied voltage, controller parameters, volume fraction of carbon nanotubes, spring, and shear constants of foundation. Numerical results indicate that by applying the positive voltage and transverse magnetic field the optimum dimensionless frequency of the system decreases. [ABSTRACT FROM AUTHOR]