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To develop lightweight and biomimetic structural materials, in this paper, the compressive deformation and mechanical properties of the grid beetle elytron plate (GBEP) with the same core volume as the end-trabecular beetle elytron plate (EBEP) under compression were investigated for the first time. (1) The B-type deformation mode of trabeculae is clarified, which is a higher stage of independent deformation than the Φ-type deformation mode in the beetle elytron plate (BEP). Additionally, the four deformation modes of the BEP are divided into three stages in succession from easy to difficult: C-type, Φ-type and S (B)-type deformation. This paper verifies that the compressive strength and energy absorption capacity of the GBEP increase by 35% and 87%, respectively, relative to those of the grid plate (GP) with the same volume. (2) Although the number of trabeculae of the GBEP is significantly less than that of the EBEP, each trabecula in the GBEP has one more honeycomb wall constraint than each trabecula in the EBEP. The increase range of the compressive properties of the GBEP relative to the GP is greater than that of the EBEP relative to the honeycomb plate (HP). This confirms the prediction that the compressive properties can be effectively improved by appropriately increasing the constraints on the trabeculae. This paper deepens and enriches the knowledge regarding the biomimetic application system of BEPs, lays the foundation for GBEPs, whose preparation is convenient, and accelerates the applications of GBEPs. [ABSTRACT FROM AUTHOR]

This paper is dedicated to the study of global (at the sandwich scale) and local (at the component scale) buckling in sandwich structures. This approach relies on the basis of an analytical model able to capture both local and global instabilities [Léotoing, L., Drapier, S. and Vautrin, A. (2002). First Applications of a Novel Unified Model for Global and Local Buckling of Sandwich Columns, European Journal of Mechanics A/SOLIDS, 21(4): 683-701]. Results from this model are used to provide simple design rules by assessing the combinations of geometrical and material parameters which control these instabilities. From there, design diagrams are extracted which permit very quickly to select sandwich configurations more susceptible to develop local or global phenomena. These design diagrams constitute a precious guide at the predesign stage of sandwich structures. Then, two distinct FE models are presented and compared. The ability of a reduced size FE model to capture local as well as global instabilities is demonstrated. Eventually, the predicted loads and wavelengths from both FE simplified model and analytical model are shown to correlate very well. Thus, analytical wavelengths give accurate evaluations of the mesh element size for a low time-consuming but accurate FE model which can be easily extended to fully non-linear computations of sandwich panels. [ABSTRACT FROM AUTHOR]

This paper presents an analytical approach to investigate the nonlinear dynamic response and vibration of shear deformable imperfect eccentrically stiffened sandwich plate with functionally graded material (FGM) on elastic foundation using both of the first-order shear deformation plate theory and stress function with full motion equations (not using Volmir's assumptions). The thick sandwich plates are assumed to rest on elastic foundation and subjected to mechanical loads in thermal environment. Numerical results for dynamic response of the eccentrically stiffened thick sandwich plates are obtained by Runge–Kutta method. The results show the influences of geometrical parameters, material properties, imperfections, the elastic foundations, eccentric stiffeners, mechanical loads and temperature on the nonlinear dynamic response and nonlinear vibration of functionally graded sandwich plates. The numerical results in this paper are compared with the results reported in other publications. [ABSTRACT FROM AUTHOR]

Auxetic cellular solids in the forms of honeycombs under blast load have great potential in a diverse range of applications, including core material in sandwich plates composite components. Based on Reddy’s first-order shear deformation plate theory, this paper presents an analysis of the nonlinear dynamic response and vibration of sandwich plates with negative Poisson’s ratio in auxetic honeycombes on elastic foundations subjected to blast and mechanical loads. A three-layer sandwich plate is considered discretized in the thickness direction by using analytical methods (stress function method, approximate solution), Galerkin method, and fourth-order Runge-Kutta method. The results show the effects of geometrical parameters, material properties, mechanical and elastic foundations on the nonlinear dynamic response, and vibration of sandwich plates. [ABSTRACT FROM AUTHOR]

The works that have been already published on sandwich face wrinkling consider isotropic or almost isotropic sandwich configurations. Hence, only the critical wrinkling load needs to be evaluated in the principal compressive stress direction. This is insufficient for a sandwich panel with a higher degree of anisotropy. This paper presents a method for estimating the wrinkling behavior of highly anisotropic sandwich panels under biaxial loading. The method is based on the assumption that wrinkling occurs at the angle where the ratio of applied load to sustainable wrinkling loads reaches a global maximum. In addition to the description of the analytical theories, the paper presents comparisons with finite element calculations and testing of real sandwich configurations. The results indicate that the derived model works excellently both for uni- and biaxial loadings, though a small factor of safety is required as with all other standard wrinkling theories. [ABSTRACT FROM AUTHOR]

The problem of face wrinkling in sandwich structures was identified as an important failure mode and first analyzed in 1940 by Gough et al., who used a Winkler-type elastic foundation to model the core. This work was followed by experiments and further analysis by many others. Until 1966 all of the research was devoted to uniaxial compression loading. However, in many applications, such as naval and aircraft structures, panels are subjected to biaxial loading. Such loadings were first analyzed by Plantema in 1966 for the case of sandwich constructed of isotropic materials. Sullins et al. suggested an interaction equation that can be used as a criterion of wrinkling under compression in the principal directions. This equation is formulated in terms of the ratios of the principal compressive stresses to the corresponding wrinkling stresses. More recently Fagerberg and Vonach and Rammerstorfer considered the case of sandwich with orthotropic facings. The present work attacks the subject problem using three different models for the core. One model uses a simple Winkler elastic foundation approach. The second model, following Hoff and Mautner [Hoff, N.J. and Mautner, S.E. (1945). The Buckling of Sandwich-Type Panels, Journal of the Aeronautical Sciences, 12: 285-297.], uses a linear model for the decay in deformation from the core-facing interface, while the third model, following Plantema [Plantema, F.J. (1966). Sandwich Construction, John Wiley & Sons, Inc., New York.], uses an exponential decay. [ABSTRACT FROM AUTHOR]

This paper focuses for the first time on the static analysis of sandwich plates with functionally graded faces and homogeneous core by an nth-order shear deformation theory and meshless global collocation method. The meshless global collocation method approximates the solutions of governing differential equations based on the nth-order shear deformation theory using all nodes in the problem domain. The deflection and stress of a simply supported sandwich plates under sinusoidal load are calculated to verify the accuracy and efficiency of the present theory. [ABSTRACT FROM AUTHOR]

This paper investigates the nonlinear response of doubly curved functionally graded material sandwich panels resting on elastic foundations, exposed to thermal environments and subjected to uniform external pressure. The material properties of both face sheets and core layer are assumed to be temperature dependent, and effective material properties of functionally graded material layers are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Formulations are based on first-order shear deformation shell theory taking geometrical nonlinearity, initial geometrical imperfection, Pasternak type elastic foundations, and tangential edge constraints into consideration. Approximate solutions are assumed to satisfy simply supported boundary conditions and Galerkin procedure is applied to derive expressions of buckling loads and nonlinear load–deflection relation. The effects of material, geometry and foundation parameters, face sheet thickness ratio, initial geometrical imperfection, thermal environments and degree of tangential restraint of edges on the snap-through instability, and nonlinear response of spherical and cylindrical functionally graded material sandwich panels are analyzed and discussed in detail. [ABSTRACT FROM AUTHOR]

In this paper, we study the nonlinear dynamic response of higher order shear deformable sandwich functionally graded circular cylindrical shells with outer surface-bonded piezoelectric actuator on elastic foundations subjected to thermo-electro-mechanical and damping loads. The sigmoid functionally graded material shells are made of the metal–ceramic–metal layers with temperature-dependent material properties. The governing equations are established based on Reddy’s third-order shear deformation theory using the stress function, the Galerkin method and the fourth-order Runge–Kutta method. Numerical results are given to demonstrate the influence of geometrical parameters, material properties, imperfection, elastic foundations, and thermo-electro-mechanical and damping loads on the nonlinear dynamic response of the shells. Accuracy of the present formulation is shown by comparing the results of numerical examples with the ones available in literature. [ABSTRACT FROM AUTHOR]

The natural frequencies and corresponding vibration modes of a cantilever sandwich beam with a soft polymer foam core are predicted using the higher-order theory for sandwich panels (HSAPT), a two-dimensional finite element analysis, and classical sandwich theory. The predictions of the higher-order theory are shown to be in good agreement with experimental measurements made with a simple experimental setup, as well as with finite element analysis. Experimental observations and analytical predictions show that the classical sandwich theory is not capable of accurately predicting the free vibration response of soft-core sandwich beams. It is shown that the vibration response of the cantilever soft-core sandwich beam consists of a group of five lower frequency shear (antisymmetric) modes that are followed by a group of four thickness-stretch (symmetric) modes. For the higher frequency range, the vibration modes alternate between groups of one-two antisymmetric and symmetric modes. For very high frequencies, interactive vibration response is observed. Experiments show that the damping properties of the foam core are manifest most noticeably in the case of thickness-stretch vibration modes, whereas the influence of damping on the anti-symmetric modes is insignificant. [ABSTRACT FROM AUTHOR]

A simplified three-unknown shear and normal deformations nonlocal beam theory for thermo-electro-magneto mechanical bending analysis of a nanobeam with a functionally graded material core and two functionally piezomagnetic layers is studied in this paper. The assumed structure is subjected to mechanical, thermal, electrical, and magnetic loads. An initial applied voltage and magnetic load is considered on the functionally graded piezomagnetic material layers. Eringen’s nonlocal constitutive equations are considered in the analysis. Governing equations are derived according to the present refined theory using the principle of virtual displacements. The numerical results including the deflection, electric, and magnetic potential distribution are calculated in terms of important parameters of the problem such as applied electric and magnetic potentials, two parameters of temperature distribution, and nonlocal parameter. The numerical results indicate that increase in applied electric potential increases the deflection unlike the applied magnetic potential that decreases the deflection. Furthermore, it can be concluded that increasing the nonlocal parameter leads to increase in the deflection. [ABSTRACT FROM AUTHOR]

This paper presents the free vibration analysis of composite thick rectangular plates, based on Reddy’s higher order shear deformation theory (HSDT). The plate theory ensures a zero shear-stress condition at the top and bottom surfaces of the plate and do not requires a shear correction factor. Although the plate theory is quite attractive, it could not be used in the finite element analysis. This is due to the difficulties associated with the satisfaction of the C1 continuity requirement. To overcome this problem associated with Reddy’s HSDT, a new C1-HSDT p-element with eight degrees of freedom per node is developed and used to find natural frequencies of thick composite plates. The formulation is easily implemented into simple and efficient finite element programs in which the trigonometric hierarchical shape functions are used. A fast convergence and excellent agreement with the known results in the literature are obtained using only one element. Besides, the effects of the boundary conditions, core to face sheet thickness ratio, Young’s modulus ratio on the natural frequencies are investigated through the analysis of these numerical results. [ABSTRACT FROM AUTHOR]

This paper investigates the deformation and failure behaviors of hybrid layered beams consisting of woven carbon fiber-reinforced polymer composite and shape memory polymer layers subjected to flexural loading. The temperature of the shape memory polymer layer was controlled by using electrical resistive heating of the woven carbon fiber-reinforced polymer layers. Three-point bending tests were then conducted on the layered beams, and the variation in the beam flexural stiffness with temperature was examined. The failure characteristics of the layered beams were also studied by microscopic observations of the tested specimens. In addition, a three-dimensional finite element analysis was performed to determine the beam flexural stiffness and the stress states in the layered beams. The predicted flexural stiffnesses were found to be in reasonable agreement with the experimental data, and the stress results were used to better understand and explain the experimental findings on the beam failure. The present results can be useful in the design and developments of high performance material systems with variable stiffness properties for aerospace morphing applications. [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]

This paper analyzes the bending response of functionally graded skew sandwich plates with graded layer as face sheet/core using higher order shear deformation theory in the frame work of finite element method considering through-the-thickness variation of displacements. The assumed kinematics field incorporates the quadratic variation of thickness co-ordinate in defining the transverse displacement. The C0 finite element formulation has been done efficiently to overcome the problem of C1 continuity associated with the higher order shear deformation theory. For this, a rectangular isoparametic Lagrangian element with nine nodes and 13 nodal unknowns at each node is developed. Two types of plates are modeled: functionally graded skew plates with graded face sheets and graded layer as core part. By considering the symmetry of the plate, different combinations of bottom-core-top thickness has been considered for the numerical study. Wide variety of numerical problems are presented for functionally graded sandwich plates with various skew angles, thickness schemes, aspect ratio, thickness ratio and boundary conditions. It is noticed that isotropic plates exhibit diverge response in comparison with graded plates. Also, power law exponent and skew angle are vital parameters that dictate the response of the plate under bending. [ABSTRACT FROM AUTHOR]

In this paper, a new higher-order shear and normal deformation theory for the bending and free vibration analysis of sandwich plates with functionally graded isotropic face sheets is developed. The number of unknown functions involved in the present theory is only five, as against six or more in case of other shear and normal deformation theories. The theory accounts for hyperbolic distribution of the transverse shear strains and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factor. The boundary conditions for the plate are assumed to be simply supported in all edges and in the static analysis, the plate is assumed to be subjected to a sinusoidally distributed load. Both symmetric and non-symmetric sandwich plates are considered. The equations of motion are obtained using Hamilton’s principle. Numerical results of present theory are compared with three-dimensional elasticity solutions and other higher-order theories reported in the literature. It can be concluded that the proposed theory is accurate and efficient in predicting the bending and free vibration responses of sandwich plates with functionally graded isotropic face sheets. [ABSTRACT FROM PUBLISHER]

The novelty of this paper is the use of a new four-variable refined plate theory for thermal buckling analysis of functionally graded material (FGM) sandwich plates. Unlike any other theory, the present new theory is variationally consistent and gives four governing equations. The number of unknown functions involved is only four, as against five in case of other shear deformation theories. In addition, the theory, which has strong similarity with classical plate theory in many aspects, accounts for a quadratic variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. Material properties and thermal expansion coefficient of the sandwich plate faces are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are assumed as uniform, linear, and nonlinear temperature rises across the thickness direction. The effects of aspect and thickness ratios, gradient index, loading type, and sandwich plate type on the critical buckling are all discussed. [ABSTRACT FROM PUBLISHER]

Following paper Part I, this article investigates the last step of ThermHex process namely fusion bonding. The critical point of the fusion bonding step is to prevent catastrophic deformation (collapsing) of cell walls under heat and pressure. This demands a rapid heating rate and short heating time to keep sufficient stiffness for the inner part of cell walls against the pressure applied on the honeycomb. Hence, in this work the transient heat transfer behavior during the fusion bonding is investigated by using a finite element model for the detailed hexagonal unit cell. Furthermore, a mathematical model is developed to analyze the deformation of molten cell walls and their gradual contact to the skin strips. The experiments based on the talc-filled polypropylene material have been performed to validate the analytical model. Consequently, the optimal fusion bonding conditions can be determined to ensure good quality for the final products. [ABSTRACT FROM AUTHOR]

An experimental and analytical study is presented to investigate the nonlinear behavior of foam core sandwich plates subjected to in-plane shear loads. Due to the low flexural stiffness of sandwich structures, the geometrical nonlinear deformation effects tend to appear earlier in foam core sandwich plates than in other laminated and sandwich plates. However, the analysis performed is applicable to any laminated or sandwich composite plate. In studies presented herein the Theorem of Minimum Potential Energy has been used to determine the deflections, strains, and stresses in the plate. Polynomial functions are used that satisfy all of the boundary conditions. It is seen from the analytical results that the lateral deflection and the in-plane shear strains and stresses are nonlinear functions of the applied loads. In addition, the in-plane normal strains do occur under the laterally applied loads which cause the inequality of principle strains between the compressive face strains and the tensile face strains. [ABSTRACT FROM AUTHOR]

Compression failure of sandwich specimens with glass/vinylester face sheets over PVC foams has been experimentally examined using an end loading test fixture based on the ASTM C 364 standard. The main objective of the research was to examine the roles of the faces and core in the mechanism of failure and ultimate load carrying ability of the structure. A range of PVC foam densities, core thicknesses, and specimen lengths were examined. Failure modes were identified, and compression strengths were compared to analytical predictions. Short specimens failed by compression failure of the face sheets up to a gage length that increased with increased foam density, and decreasing core thickness. At intermediate gage lengths it was found that specimens with a thick low density core failed in an anti-symmetric face wrinkling mode, while long specimens failed by global buckling in the fundamental buckling mode. Predictions of the failure loads were found to be in reasonable agreement with experimental results. [ABSTRACT FROM AUTHOR]

A four noded plate element based on a refined higher order shear deformation theory is developed for the analysis of composite and sandwich plates. This plate theory satisfies the conditions of inter-laminar shear stress continuity and stress free top and bottom surfaces of the plate. Moreover, the number of independent unknowns is the same as that in the first order shear deformation theory. The inter-elemental continuity, as desired by the plate theory, is fully satisfied in the present element. Numerical examples of composite and sandwich plates are solved to validate the element. Some new results are also presented. [ABSTRACT FROM AUTHOR]

Corrugated sandwich panels are widely used in engineering applications for their excellent energy absorption and lightweight. In this research, the mechanical response of aluminum corrugated sandwich panels subjected to three-point bending is investigated experimentally, numerically, and theoretically. In the experiments, the sandwich panels were loaded under two conditions, namely base indentation and node indentation. A parametric study is conducted by ABAQUS/explicit to investigate the effects of geometric configurations (corrugation angle, core height, and core thickness) on the deformation mode, peak force, and energy absorption. Both peak force and specific energy absorption vary with the geometric parameters. Theoretical models are further developed to predict the force–displacement curves of the panels under the two loading conditions. The theoretically predicted crushing force is in good agreement with both the experimental and simulated results. Finally, the non-dominated sorting genetic algorithm II is adopted to optimize the geometric configuration to improve the specific energy absorption and reduce the weight of corrugated sandwich panels. [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]

Based on classical dynamic cylindrical cavity expansion theory, a nine-step penetration and perforation process of aluminum foam sandwich targets by truncated cone-nosed projectiles are developed theoretically. In the theoretical model, the friction, shear strength, and the force for tearing the cells in the core at the periphery of the projectile are considered, and the resistance force and instantaneous velocity are achieved from this process. On this basis, the effects of the geometry of projectiles, core thickness, and impact velocities of projectiles on absorbed energy are also analyzed. Simple composite failure criteria will be applied in the fracture and perforation of the face sheet, core, and back sheet. It is shown that the diameter of projectile and core thickness have significant influence on the ballistic velocity of the projectile, which is important for the impact response and absorbed energy of the sandwich. Numerical simulation at various impact velocities is also performed, and there is a good agreement between the numerical predictions and the analytical measurements. [ABSTRACT FROM AUTHOR]

Using harmonic differential quadrature method, an approach to analyze sandwich cylindrical shell panels with any sort of boundary conditions under a generally distributed static loading, undergoing elasto-plastic deformation is proposed. The faces of the sandwich shell panel are made of some isotropic materials with linear work hardening behavior while the core is assumed to be an isotropic material experiencing only elastic behavior. The faces are modeled as thin cylindrical shells obeying the Kirchhoff–Love assumptions. For the core material, it is assumed to be thick and the in-plane stresses are negligible. Upon application of an inner and outer general lateral loading, the governing equations are derived using the principle of virtual displacements. Using an iterative approach, named elasto-plastic harmonic differential quadrature method (EP-HDQM), the equations are solved. The obtained results are compared with the results from finite element software Ansys for different sandwich shell panel configurations. Then, the effects of changing different parameters on the stress and displacement components of sandwich cylindrical shell panels in different elasto-plastic conditions are investigated. [ABSTRACT FROM AUTHOR]

An accurate discrete model is presented here for the analysis of simply supported web-core sandwich plates. In this model, the face plates are analysed using the equations of 3D elasticity and for the webs a plane stress idealization is used to model the kinematics of transverse bending while simple one-dimensional classical models are employed for lateral bending and torsion. Thus, this model accounts for the non-classical effects of transverse shear deformation and transverse thickness-stretch in the face-plates and the webs. It is shown that this model is capable of accurately capturing the effects of secondary local bending of the face-plates between the webs on the displacement and stress fields. Results obtained by this rigorous approach are used to highlight the errors of the commonly used model based on the classical hairbrush hypothesis for the face-plates. [ABSTRACT FROM AUTHOR]

In this work, the functionally graded honeycomb structures with defects are investigated. It is shown how the patterns and locations of defects, as well as the density gradients, can affect the in-plane dynamic crushing behavior of honeycombs. Numerical results show that due to missing vertical cell walls, the deformation process for the transverse-vertical mixing defects is more complicated than that for pure vertical defects. For the honeycombs with negative density gradient, the I-shape deformation band is dominant during the dynamic crushing. However, the honeycombs with positive density gradient are crushed to densification with the combination of the first and second deformation bands. It is revealed that the ability of energy absorption could be improved by introducing the functional graded property. Moreover, under a high impact velocity, the gradient displays a high sensitivity on the energy-absorption capability of the honeycomb structures. At the early stage of crushing, the honeycomb structures with the positive density gradient behave the stronger capacity on energy absorption than those with the negative one. The energy-absorption curves for systems with positive and negative densities are symmetric about the homogeneous structures. As the compression proceeds, for the honeycombs with positive and negative density gradients, the trends of energy-absorptive abilities go into reverse. [ABSTRACT FROM PUBLISHER]

The increasing application of functionally graded materials in the aerospace structures requires the adoption of accurate modeling strategies. The original formulation of the Refined Zigzag Theory is here extended to the bending and free vibration analysis of sandwich plates embedding functionally graded layers, either as faces or core. Extensive numerical investigation shows the superior predictive capabilities of Refined Zigzag Theory over both First-order Shear Deformation Theory and Third-order Shear Deformation Theory, if compared with the reference three-dimensional elasticity or high-fidelity FEM solutions. In virtue of its accuracy and of the C0–continuity requirement for shape functions, Refined Zigzag Theory can be adopted to formulate reliable and computationally efficient finite elements suited for large-scale analyses of both traditional and functionally graded structures. [ABSTRACT FROM PUBLISHER]

The failure modes of open weave (latticed) sandwich skins under biaxial compression load are analysed. Due to the latticed structure of these sandwich face sheets, they are able to transfer loads in both directions. Tests show a distinct non-linear correlation between load and deformation. This non-linear load-deflection-behavior indicates that the failure may be induced by geometrical imperfections. Based on this assumption and measured geometrical imperfections, a mathematical model for the latticed face sheet consisting of beams under compression is derived. Several beams are combined within one or two cells of the honeycomb core to describe the failure modes. Furthermore, biaxial loading is analysed by using the finite element method. Experimental results are in good agreement with failure loads derived by analytical and by finite element method analyses as well. [ABSTRACT FROM PUBLISHER]

An elastic-plastic model was developed for predicting the blast response of a foam-core, curved composite sandwich panel. A multi-layered approach was used to distinguish facesheets and core deformations. Core compressibility and transverse shear through the thickness were accounted for using linear displacement fields through the thickness. The predicted solution from the elastic-plastic model was shown to compare well with FEA from ABAQUS Implicit. A parametric study showed that blast resistance of the sandwich shell is increased by allowing cores to undergo plastic crushing. Very thick and shallow shells derive much of their resistance to blast from core crushing. Strong, dense foam cores did not increase the blast resistance of the curved sandwich panel but allowed facesheets to fracture while the core remained elastic. [ABSTRACT FROM PUBLISHER]

The dynamic behavior of soft-core sandwich plates is investigated. A high-order finite element concept that has been developed for the dynamic analysis of multi-layered plate structures with stiff and compliant layers is applied to the soft-core sandwich plate. The application to sandwich plates aims to validate the general model through comparison with experimental and analytical benchmarks and to throw light on the unique structural response of the sandwich plate. The model introduces the core’s three-dimensional stress and deformation fields using a high-order kinematic assumption that is based on the closed-form solution of the static governing equations of the core. The first-order shear deformation laminated plate theory is used for the face sheets. The combination of the high-order theory with the finite element concept aims to extend the application of the theory to more general layouts, to reduce the computation effort needed for a three-dimensional analysis, and to address some of the obstacles due to differences in length scales and elastic properties. The validity and the capabilities of the formulation are examined through comparison with experimental and analytical results taken from the literature. In addition, the static, free vibration, and dynamic behaviors of an ‘L’ shaped sandwich plate subjected to localized loads and boundary conditions are numerically studied. The formulation, the comparison with experimental and analytical benchmarks, and the numerical study highlight the three-dimensional effects and reveal unique aspects of the dynamic response of soft-core sandwich plates. [ABSTRACT FROM AUTHOR]

In this article, the static analysis of sandwich plates is performed by radial basis functions collocation, according to the Murakami's Zig-Zag function theory. The Murakami's Zig-Zag function theory accounts for through-the-thickness deformation, by considering a Zig-Zag evolution of the transverse displacement with the thickness coordinate. The equations of motion and the boundary conditions are obtained by the Carrera's unified formulation, and further interpolated by collocation with radial basis functions. [ABSTRACT FROM PUBLISHER]

This article presents a study of the linear transient response of composite plates using radial basis functions and collocation method. We use the Kansa method and radial basis functions in a pseudo-spectral framework. The first-order and a third-order shear deformation plate theories are used. It is shown that the present method produces highly accurate displacements and stresses when compared with the available results in the literature. [ABSTRACT FROM PUBLISHER]

In the present study, vibration and damping analysis of cylindrical sandwich panels containing a viscoelastic flexible core based on the high-order theory of sandwich structures is investigated. A layerwise formulation is developed to study the applicability of the high-order theory. The face sheets are considered as composite laminates with cross-ply layup that follow first-order shear deformation assumption and the core is considered as a linear viscoelastic medium with out-of-plane stresses only. The field equations along with the boundary conditions are derived via the application of Hamilton’s principle. A closed-form solution is developed for simply supported boundary conditions and a comparison is made with available results in the literature to verify the high-order and layerwise solution results. Finally, the influence of parameters including the core stiffness, the core to the face sheets thickness ratio, and the core damping on the applicability of the high-order theory, and variation of natural frequencies and modal loss factors of the sandwich panel are investigated. The results demonstrate a good agreement between the high-order and layerwise theories for small core stiffnesses, and for a wide range of the core to the face sheet thickness ratio and core damping. [ABSTRACT FROM AUTHOR]

This article presents a theoretical analysis for predicting the initial stiffness E*, and plastic collapse strength σ*pl of BCC micro-lattice blocks under compressive loading. This theoretical analysis is based on the observed deformation mechanisms, and can, in principle, be developed to predict the elastic properties of other micro-lattice structures. The analytical solutions are verified by comparing the predictions with FEM data using 1D beam and 3D solid elements and uniaxial compression tests on samples fabricated by selective laser melting. The FEM predictions using the 3D solid elements agree well with the experimental data for a wide range of strut aspect ratios, d/L. In addition, the range of applicability of the analytical model and the FEM predictions using beam elements are clarified. [ABSTRACT FROM AUTHOR]

Sandwich panels manufactured using thermoplastic fiber-metal laminates (FML) skins and an aluminum foam core were tested under quasi-static and low-velocity impact loading conditions. The quasi-static properties of the sandwich beams were evaluated using the three-point bend test geometry. Energy absorbing mechanisms such as buckling and interfacial delamination in the FML skin, as well as indentation, crushing, and densification in the aluminum foam have been observed to contribute to the excellent energy absorbing characteristics offered by these systems. The low-velocity impact behavior of the sandwich panels was evaluated using an instrumented dropping weight impact tower and modeled using an energy balance approach. A breakdown of the energy absorption revealed that these sandwich structures absorb much of the impact energy due to contact and bending effects. Finally, four-point bend testing after low-velocity impact revealed that these systems offer excellent residual flexural strength with relative values remaining close to 80% of the original strength after a 32 J impact. [ABSTRACT FROM AUTHOR]

This study shows that a simple approach to stiffness tailoring of composite face sheets can improve the performance of sandwich panels under compressive loading when delaminations are present. The simple stiffness tailoring concept used here is to reposition of all 0° material (aligned with the loading direction) into regions of certain width near the edges of the sandwich panel. This concept has been shown to improve the buckling and postbuckling performance of solid plates and to offer control of delamination growth. To evaluate this tailoring design concept in sandwich panels, numerical simulations of onset and propagation of the delamination growth were conducted with uniform face sheets and tailored face sheets. The delamination front tracing method previously developed by the authors was used to perform the delamination growth analysis. The interfacial elements, which allow the growth of the delamination front to be traced, are placed at the interface between the top face sheet and the core in the undelaminated region. They enable calculation of the strain energy release rates and application of a fracture mechanics delamination growth criterion. Gap elements were used to avoid interfacial overlap. Based on the numerical study, the improvement in the ultimate load provided by the simple stiffness tailoring concept ranges from 80% to 100%, depending on the extent of tailoring. Substantial improvements in the residual strength and stiffness, after significant delamination growth, can also be observed. Therefore, this article provides a potential design concept that can improve the damage tolerance of sandwich panels without adding weight. [ABSTRACT FROM AUTHOR]

The buckling behavior of a disbond in a sandwich beam is analyzed by modeling the sandwich as a beam on a Winkler foundation. The foundation stiffness is derived through a stress function approach, modeling the core as a two-dimensional, orthotropic material in plane strain. When the resulting stiffness term is used in the Winkler foundation model, the predicted buckling loads vary from the specimen test results by only 1.7% (with a standard deviation of 2.3%). This is the most accurate published prediction of disbond buckling and is discussed in terms of previous studies. An extensive specimen test program is described, the results of which are used to validate the Winkler foundation model. The buckling load, as a function of core thickness, is found to have a minimum when the core thickness is approximately equal to the natural wrinkling half-wavelength of the sandwich. Further, a characteristic curve is found using the wrinkling wavelength and the Euler buckling load as normalizing values. A semi-empirical formula for the buckling load is developed from a non-dimensional analysis and predicts the specimen test results to within 2.8% (standard deviation of 3.6%). [ABSTRACT FROM AUTHOR]

This article presents an analytical approach for evaluating the buckling load of sandwich panels made of hybrid laminated faces and a transversely flexible core. Useful design indications are obtained once the influence of main parameters influencing the structural response is examined. The proposed model is based on a priori assumption of the displacement field through the thickness, which is composed of two sets of modal configurations, one symmetric and one antisymmetric, besides a pure compressive mode. An equivalent `single layer approach', considering all displacement components (u, v, w) that linearly vary across the panel thickness, is used. For simply supported flat sandwich panels subjected to in-plane biaxial and shear loads, the Rayleigh-Ritz method is used to evaluate the buckling loads. Predictions of the proposed model are compared with those obtained by other available theoretical models and with experimental results. Finally, the best arrangement of sandwich panels, corresponding to the maximum buckling loads, is investigated by varying the parameters of both the faces and the core material. [ABSTRACT FROM AUTHOR]

This article presents an approach to facilitate comparison and optimization of sandwich material combinations. Equivalent homogenized sandwich material properties (bending stiffness, density, and cost) are presented graphically in material selection charts to enable an efficient performance per cost evaluation. The effects of core shear deformations and panel production costs can be included in those sandwich material selection charts. [ABSTRACT FROM AUTHOR]

This article deals with the linear static and buckling analysis of an asymmetric square sandwich plate with orthotropic stiffness properties in the face layers. Two analytical formulations related to thin and thick face layers, respectively, have been taken from (Zenkert, D. (1995). An Introduction to Sandwich Construction, Chameleon Press Ltd, London, UK (ISBN 0 947817 77 8)), slightly modified to account for unequal faces, orthotropic properties in the face layers, and individual Poisson's ratios, and applied to square sandwich plates of I m lateral dimension and a variety of different face layer thickness. All cases assume simply supported edges. The obtained deflections and buckling loads are compared with the results of a 3D analysis (Meyer-Piening, H.-R. (2004). Application of the Elasticity Solution to Linear Sandwich Beam, Plate and Shell Analyses, J. of Sandwich Structures & Materials, 6(4): 295-312) and of finite element calculations. The objectives of this study are to gain insight into the limits of validity of the published formulas in view of unequal thick face layers and orthotropic properties. The obtained results are meant to serve as a benchmark for further studies. [ABSTRACT FROM AUTHOR]

Static and dynamic analyses of sandwich beams are performed by means of a finite element approach based on: (i) the Hermitian Zig-Zag theory, previously developed by the authors and (ii) the sublaminates approach; the possibility to divide not only the beam length but also its thickness in several sub-domains leads to improved capabilities in describing through-the-thickness distributions of displacements, strains and stresses. The proposed approach is also able to predict the response of damaged beams. The sandwich core is substituted by an equivalent orthotropic layer whose engineering constants are calculated using models proposed in literature. The effectiveness of the approach is demonstrated presenting and discussing some numerical results (vibration frequencies and static response for undamaged beams, static response of damaged beams). It is shown that the proposed approach is valid in determining global and local responses of sandwich beams. [ABSTRACT FROM AUTHOR]

Dynamic modeling of interfacial cracks between the skin and core materials was performed and numerical simulation was undertaken to study the feasibility of crack detection. The cracks were modeled in the way as they were physically in the sandwich beam structures using the finite element method. Numerical simulation of impact-hammer hit was applied to the finite element models to calculate the time history of strain responses along the sandwich beams. Dynamic crack opening and closure was considered with friction at the surfaces of interfacial cracks. Thus, nonlinear dynamic analysis was conducted. Then, the Fast Fourier Transform (FFT) was used to transform the time responses to frequency responses. The effects of interfacial cracks were examined in both time and frequency plots by comparing those responses between the damaged structure and the intact structure. The present study showed that the effect of crack closure was important so that nonlinear analysis was necessary to represent the interfacial crack behaviors properly. The strain response from nonlinear dynamic analysis (i.e. simulated impact hammer hit) had great potential for detecting and locating a small size of interfacial crack in a sandwich beam structure. [ABSTRACT FROM AUTHOR]