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1

Mathematical model of modified classical lamination theory for foam core sandwich composites

Kumar S.J. Amith, Kumar Ajith S.J.

Composites Theory and Practice

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2023

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R. 23, nr 4

220--225

EN

Elastic properties are important quantities in the modelling and analysis of sandwich composite structures. The stability of sandwich composites mainly depends on their elastic properties, which in turn depend on the elastic properties of its constituents namely, the core and face skin. Several models have been proposed to predict the elastic constants of core materials such as honeycomb and foam. A foam core may be open-cell foam or closed-cell foam. The present work is focused on the hexagonal cells of a honeycomb grid core and closed-cell polymer syntactic foam core. The honeycomb is considered to be orthotropic with nine independent elastic properties. However, the overall structural performance of the honeycomb core is mainly influenced only by out-of-plane elastic properties. On the other hand, the syntactic foam is considered to beisotropic with two independent elastic constants namely, the modulus of elasticity and Poisson’s ratio. The face skin material may be isotropic with two independent elastic constants or orthotropic with nine elastic constants under three-dimensional loading. The present work is focused on predicting the elastic properties of a honeycomb core, syntactic foam and a glass/epoxy composite using existing theoretical models. Thereafter, the elastic properties of the syntactic foam and glass/epoxy composite are later used to establish the elastic constants for syntactic foam core sandwich composites using modified classical lamination theory (MCLT). The results reveal that the reviewed theoretical models for the honeycomb core, syntactic foam, fiber-reinforced polymeric (FRP) glass/epoxy face skins and sandwich composites are validated by the experimental results.

2

Investigating the effect of honeycomb grid cell size on structural performance of stiffened syntactic foam core sandwich composite

Kumar Amith S.J., Kumar Ajith S.J.

Composites Theory and Practice

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2023

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R. 23, nr 4

202--208

EN

Syntactic foam core composite sandwich structures are potential structural panels because of their high specific properties. The chief ingredient of a syntactic foam is dry fly ash cenospheres, which play a vital role in the mechanical properties of syntactic foam in relation to its volume fraction. In the present investigation, the concept of confining foam in the cells of a honeycomb grid structure was adopted to improve the mechanical properties of composite sandwich structural panels. Experimental investigations were carried out to evaluate the thermal stability and mechanical properties of a honeycomb grid stiffened syntactic foam core composite sandwich as per ASTM standards. The results of the investigations reveal that the syntactic foam confined in the hexagonal cells of the honeycomb grid structure considerably improves the mechanical properties by 20% to 180% than compared with syntactic foam core sandwich composites without a honeycomb grid structure. The cell walls of the honeycomb grid structure hinder the propagation of cracks under loading conditions. The damage tolerance capacity is attributed to the cell size of the honeycomb structure. Interfacial bonding of the constituent materials leads to improved mechanical properties.

3

Industrial applications of computational fluid dynamics

Holdo A. E.

International Journal of Applied Mechanics and Engineering

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2002

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Vol. 7, no 1

85-105

EN

Computational Fluid Dynamics (CFD) has increased in usage within many areas of industry. In a large number of cases CFD is seen as an extension of CAD or FEM modelling and a long term vision is the integration of CFD with CAD and FEM structural analysis. Because of this it is now commonplace to import CAD based solid models into CFD packages for the use of studies. This is in principle a very practical approach as it saves model generation time. However, with such model generation there are many concerns such as the correct mesh density at the correct locations and the representation of curvature. The CAD model may appear smooth and be constructed by polynomials, but the resulting mesh may not be as smooth particularly if a Cartesian mesh or a mesh with lower order polynomials are used by the CFD solver. Alternative meshing strategies such as non-structured and structured meshes are also shown and results are discussed with reference to the integration of CAD with CFD. Another important issue for the industrial application of CFD is turbulence modelling. A comparison in terms of results and computing time between Reynolds Averaged Navier Stokes (RANS) modelling and Large Eddy Simulation (LES) is also given and finally it is suggested that meshing may be best taken care of by using solution adaptive meshes both for the prediction of main flow features as well as turbulence modelling.