In this TLP, the elastic, yielding and densification behaviour of a simple honeycomb structure has been studied experimentally. It is shown that the deformation of a honeycomb structure is made up of 3 main regions: an elastic region, which ends when the maximum stress in the cell faces becomes equal to the flow stress of the material, allowing the cells compact at a constant stress, followed by a region in which the load rises rapidly with increasing strain, as the honeycomb is compacted.
Quantitative descriptions of the behaviour have been derived and compared with the experimental measurements. These show that the deformation behaviour of a honeycomb is determined not by the axial compression of those faces parallel to the loading axis, but by the bending of faces lying at some angle to the loading axis.
It has been shown that these ideas can be extended to describe the deformation behaviour of more irregular structures, such as foams. For foams that are isotropic and have open cells, it is predicted that the relative elastic modulus varies with the square of the relative density, consistent with observations in the literature.
The uses of such structures are described and it is shown that in isotropic open-cell foams, sandwich structures are required to obtain improved specific stiffness in bending. The enhanced stiffness of cellular structures such as wood arises from modifications to the structure that gives a different dependence of the relative stiffness on the elastic modulus.
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