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Honeycomb materials are commonly used as cores for sandwich panels. While empirical evidence exists showing that the transverse shear strength of a honeycomb core is affected by its thickness, the accuracy of empirical guidelines and the reasons for the changes in strength are not well understood. Four-point flexural testing of sandwich beams and a detailed cellular finite element model are used to investigate transverse shear failure of Nomex™ honeycomb core material. Transverse shear strengths at varying core thicknesses were compared to manufacturer specifications and used to determine normalised strength correction factors for thickness. These factors correlated well with trends shown in previous literature, where core shear strength decreases with increasing core thickness. The failure mode investigation showed a transition between modes as core thickness increased. The thinner cores experience shear fracturing of individual cell walls followed by local cell wall buckling, intermediate thickness cores initially failed by cell wall local buckling, then fractured and larger thickness cores appeared to fail by overall cell column buckling. [ABSTRACT FROM AUTHOR]

This study presents a new higher-order refined analysis model for static and free vibration analysis of a sandwich plate with soft functionally graded material core. The governing equations are derived from equilibrium differential equations of motions. The accuracy and convergence of the present model and numerical solution are validated versus available results. Variable length width ratios, thickness ratios between skins and core and span-to-thickness of sandwich plates have been studied. Obtained results show that suggested model can achieve greater accuracy for sandwich plates with soft functionally graded material core, as compared to existing functionally graded sandwich plate analysis models and models based on finite element method. Finally, parametric study has been carried out to investigate influence of volume fraction distribution, thickness to side ratio and material properties on the plate bending and free vibration. [ABSTRACT FROM AUTHOR]

In the present study, the free and forced vibration responses of the composite sandwich plate with carbon nanotube reinforced honeycomb as the core material and laminated composite plates as the top and bottom face sheets are investigated. The governing equations of motion of hybrid composite honeycomb sandwich plates are derived using higher order shear deformation theory and solved numerically using a four-noded rectangular finite element with nine degrees of freedom at each node. Further, various elastic properties of honeycomb core materials with and without reinforcement of carbon nanotube and face materials are evaluated experimentally using the alternative dynamic approach. The effectiveness of the finite element formulation is demonstrated by performing the results evaluated experimentally on a prototype composite sandwich plate with and without carbon nanotube reinforcement in core material. Various parametric studies are performed numerically to study the effects of carbon nanotube wt% in core material, core thickness, ply orientations, and various boundary conditions on the dynamic properties of composite honeycomb sandwich plate. Further, the transverse vibration responses of hybrid composite sandwich plates under harmonic force excitation are analyzed at various wt% of carbon nanotubes and the results are compared with those obtained without addition of carbon nanotubes to demonstrate the effectiveness of carbon nanotube reinforcement in enhancing the stiffness and damping characteristics of the structures. The study provides the guidelines for the designer on enhancing both the stiffness and damping properties of sandwich structures through carbon nanotube reinforcement in core materials. [ABSTRACT FROM AUTHOR]

A sandwich structure consists of a two thin and strong facesheets, bonded to a thick lightweight core material. The mechanical response of a sandwich structure depends on the properties of its constituents. A numerical model and experimental validation of the three-point bending test of sandwich composites are presented in this study. The core material is aluminum honeycomb. The facesheets are made of IM7/Cycom5320-1, which is a carbon fiber/epoxy prepreg system. A comprehensive model of the failure under flexural loading was developed. Facesheet failure was modeled using Hashin's failure criteria. A detailed meso-scale model of the honeycomb core was included in the model. The experiments indicated that failure initiation was due to local buckling in the honeycomb core. Failure propagation was in the form of core failure, facesheet compressive failure, and interlaminar failure. The developed meso-scale model was able to accurately simulate failure initiation and propagation in the composite sandwich structure. The effect of elevated temperature on the three-point bending behavior was studied numerically as well as experimentally. An increase in test temperature to 100°C resulted in a drop of 9.2% in flexural strength, which was also predicted by the numerical model. [ABSTRACT FROM AUTHOR]

With the development of technology, the use of glass fibres and sandwich structures in a wide variety of engineering applications has had important growth in recent years because of their low self-weight and high strength when compared to conventional materials. Moreover, natural materials can be used as the core material in sandwich structures instead of conventional materials. Since synthetic materials cause a reduction of carbon release during material formation, these kinds of materials are renewable and recyclable. Therefore, in sandwich structures, renewability and recycling can be provided. In this study, dynamic properties of natural material-based sandwich composites were investigated experimentally and numerically. The effects of the thickness of the core and fibre orientation and number of layers on frequency and damping were analysed. It was observed that if the core thickness of the structure is properly optimised, this sandwich structure demonstrates better dynamic properties. Thus, sandwich materials from natural origin may offer more environmental friendly solutions compared to other materials. [ABSTRACT FROM AUTHOR]

ABSTRACT: Low order and high order shear deformation models are applied to investigate the effect of honeycomb core (transversely shear deformable) on flexural vibration of thick rectangular sandwich panel with isotropic facesheets. Strain and kinetic energy of sandwich panel are expressed in terms of material properties and structural parameters. Partial differential equations are derived based upon a variational principle. Solutions in Navier form are obtained for a simply supported rectangular panel. The effect of honeycomb core parameters, such as characteristic angle, cell wall thickness, and cell size is studied. Comparison between low order model, high order model, and finite element method is provided. It is shown that in most cases results from a high order model without facesheet shear effect are close to those from finite element analysis. [ABSTRACT FROM AUTHOR]

Compared to other core materials, honeycomb materials provide impressive mechanical performance for sandwich panels, but with less weight added to the structures. In this article, the out-of-plane compressive properties of the thermoplastic hexagonal honeycombs are investigated by using finite element analysis (FEA). Due to the fact that the vertical cell walls of the honeycombs are not perfectly straight, the out-of-plane compressive modulus and strength cannot be predicted correctly by conventional theories. Therefore, FEA methods are used in this study attempting to evaluate the compressive properties. Initially, linear buckling analysis (eigenvalue problem) is applied on the honeycomb models with various numbers of cells to obtain the relationship between the single hexagonal unit cell and the infinite honeycomb. Based on this, nonlinear large deformation FEA is performed on the unit cell model with/without imperfect geometry to obtain honeycomb compressive properties. Finally, the resulting modulus and strength of the honeycomb are compared to the other analytical results and experimental data. The FEA method shows some advantages over these conventional theories. [ABSTRACT FROM AUTHOR]