Fabrication of Auxetic Foam Sheets for Sports Applications

Allen, T, Hewage, T, Newton-Mann, C, Wang, W, Duncan, O and Alderson, A (2017) Fabrication of Auxetic Foam Sheets for Sports Applications. physica status solidi (b), 254 (12). ISSN 0370-1972

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Abstract

Auxetic materials have a negative Poisson’s ratio, which can enhance otherproperties. Greater indentation resistance and energy absorption, as well assynclastic curvature, could lend auxetic materials well to protective sportsequipment and clothing. Sheets of foam often form padding within protectiveequipment, but producing large homogenous auxetic foam samples ischallenging. The aim of this work was to investigate techniques to fabricatelarge thin sheets of auxetic foam, to facilitate future production and testingof prototype sports equipment utilizing this material. A mold was developedto fabricate sheets of auxetic foam  with planar dimensions measuring350  350 mm  using the thermo-mechanical process. The mold utilizedthrough-thickness rods to control lateral compression of foam. Sheets ofauxetic foam measuring 10  350  350 mm were fabricated and character-ized. Each sheet was cut into nine segments, with density measurementsused to determine how evenly the foam had been compressed duringfabrication. Specimens cut from corner and centre segments were subject toquasi-static extension up to 30% to obtain stress versus strain relationships,with Digital Image Correlation used to determine Poisson’s ratio. Specimenscut from the corner tended to have a marginally higher density, lowerstiffness and more consistent negative Poisson’s ratio compared to thosefrom the centre, indicating some inconsistency in the conversion process.Future work could look to improve fabrication techniques for large thinhomogenous sheets of auxetic foam.