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Proceedings 2018, 2(6), 250;

Controlling Density and Modulus in Auxetic Foam Fabrications—Implications for Impact and Indentation Testing

Materials Engineering Research Institute, Sheffield Hallam University, Sheffield S1 1WB, UK
Sports Engineering Research Team, Manchester Metropolitan University, Manchester M1 5GD, UK
Centre for Sports Engineering Research, Sheffield Hallam University, Sheffield S1 1WB, UK
Metamaterials Unit, Faculty of Science, University of Malta, Msida MSD 2080, Malta
Author to whom correspondence should be addressed.
Presented at the 12th Conference of the International Sports Engineering Association, Brisbane, Queensland, Australia, 26–29 March 2018.
Published: 13 February 2018
(This article belongs to the Proceedings of ISEA 2018)
PDF [740 KB, uploaded 27 March 2018]


Foams are commonly used for cushioning in protective sporting equipment. Volumetrically compressing open-cell polyurethane foam buckles cell ribs creating a re-entrant structure—set by heating then cooling—which can impart auxetic behaviour. Theoretically, auxetic materials improve impact protection by increasing indentation resistance and energy absorption, potentially reducing sporting injuries and burdens on individuals, health services and national economies. In previous work, auxetic foam exhibited ~3 to ~8 times lower peak force (compared to its conventional counterpart) under impacts adopted from tests used to certify protective sporting equipment. Increases to the foam’s density and changes to stress/strain relationships (from fabrication) mean Poisson’s ratio’s contribution to reduced peak forces under impact is unclear. This work presents a simple fabrication method for foam samples with comparable density and linear stress/strain relationship, but different Poisson’s ratios ranging between 0.1 and −0.3, an important step in assessing the Poisson’s ratio’s contribution to impact force attenuation.
Keywords: Auxetic; Foam; Fabrication; safety; impact; protection Auxetic; Foam; Fabrication; safety; impact; protection
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Duncan, O.; Allen, T.; Foster, L.; Gatt, R.; Grima, J.N.; Alderson, A. Controlling Density and Modulus in Auxetic Foam Fabrications—Implications for Impact and Indentation Testing. Proceedings 2018, 2, 250.

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