High Strain Extension of Open-Cell Foams

[+] Author and Article Information
N. J. Mills, A. Gilchrist

School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2IT, U.K.

J. Eng. Mater. Technol 122(1), 67-73 (Apr 22, 1999) (7 pages) doi:10.1115/1.482767 History: Received August 20, 1998; Revised April 22, 1999
Copyright © 2000 by ASME
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A uniaxial tensile stress σz applied in the [001] direction of a Kelvin open cell foam. Chains of edges, like those in bold, take the load.
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(a) The structural cell for [001] direction tension of the Kelvin foam, (b) the effective load on the half-edge BO. Its shape is shown for 20% foam strain.
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The predicted reduced stress-strain relation for the Kelvin foam loaded in the [001] and [111] directions, using Plateau border edges, plus Shulmeister’s 15 random cell prediction [[dashed_line]] with circular section edges, all for a relative density of 0.025
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The maximum edge tensile strain versus the foam tensile strain, for the Kelvin foam extended in the [001] and [111] directions, with the same parameters as Fig. 3
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Predicted variation of Poisson’s ratio with foam tensile strain, for the Kelvin foam loaded in the [001] and [111] directions as in Fig. 3, compared with El-Ratal and Mallick’s Poisson’s ratio data • 10 for a commercial PU foam (increased by 0.15 to make the comparison easier)
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(a) xy projection of a triangular prism showing two sloping edges and two half horizontal edges, in both the undeformed and deformed states, for [111] direction extension of the Kelvin foam by 20%. G lies beneath and R above the plane of the projection (b) a perspective view of the force and moments applied at G to the edge CG.
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Predicted Kelvin foam cell shape for 20% tensile strain in the [111] direction, seen in perspective with the stress axis vertical
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Stress strain curve for a PU uphoistery foam of relative density 0.021, loaded in the plane of the sheet, cycled three times to 25% strain at a nominal strain rate of 0.005 s−1 . The Kelvin foam [111] predictions are [[dotted_line]] for equiaxed cells and [[dashed_line]] for cells with edges initially at 45 deg to the stress, using E=100 MPa for the polyurethane.
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Lateral contraction in the rise – and in-plane [[dashed_line]] directions versus tensile strain for the same experiment as Fig. 8, for cycles 2 and 3




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