Why does some materials like honeycomb and re-entrant foam have negative possion's ratio?
"Real" materials do not have negative Possion's ratio. Material that is arranged in a structure and considered as if it were a "homogeneous" material can display this property. To understand why, create a FEA model of the material structure and see what happens when you apply loads.
By the way, Poisson was a person - so please give him his capital letter.
"Real" materials do not have negative Possion's ratio. Material that is arranged in a structure and considered as if it were a "homogeneous" material can display this property. To understand why, create a FEA model of the material structure and see what happens when you apply loads.
By the way, Poisson was a person - so please give him his capital letter.
Some artificial materials like AUXETIC have negative Poisson's ratio. See attachement
Because of their particular microstructure, zeolites can also exhibit a negative Poisson's ratio. You can read : "An analytical model for producing negative Poisson’s ratios and its application in explaining off-axis elastic properties of the NAT-type zeolites", from Jennifer J. Williams et al. 2007 in Acta Materialia.
A material which exhibits a negative Poisson's ratio expands laterally (gets fatter) when stretched. Foams with negative Poisson's ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.
The interested reader can refer to "Foam structures with a negative Poisson's ratio", Science, 235 1038-1040 (1987). This is the first designed negative Poisson's ratio material.
http://www.sciencemag.org/content/235/4792/1038.full.pdf
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