Auxetic Foam for Snow-Sport Safety Devices

Abstract

Skiing and snowboarding are popular snow-sports with inherent risk of injury. There is potential to reduce the prevalence of injuries by improving and implementing snow-sport safety devices with the application of advanced materials. This chapter investigates the application of auxetic foam to snow-sport safety devices. Composite pads-consisting of foam covered with a semi-rigid shell-were investigated as a simple model of body armour and a large 70 × 355 × 355 mm auxetic foam sample was fabricated as an example crash barrier. The thermo-mechanical conversion process was applied to convert open-cell polyurethane foam to auxetic foam. The composite pad with auxetic foam absorbed around three times more energy than the conventional equivalent under quasi-static compression with a concentrated load, indicating potential for body armour applications. An adapted thermo-mechanical process-utilising through-thickness rods to control in-plane compression-was applied to fabricate the large sample with relatively consistent properties throughout, indicating further potential for fabrication of a full size auxetic crash barrier. Further work will create full size prototypes of snow-sport safety devices with comparative testing against current products.

Application of Auxetic Foam in Sports Helmets

“…Auxetic foams (with a negative Poisson's ratio) have shown higher energy absorption than their conventional counterparts [31][32][33], and can be tailored to test the effect of mechanical characteristics (i.e., Young's modulus and Poisson's ratio) in complex situations (i.e., impact tests) [34,35]. Lakes originally fabricated auxetic foams through a compression and heat treatment process [36].…”

“…Open cell auxetic foams exhibit peak forces~3 to~8 times lower than their unconverted counterparts when impacted in scenarios similar to sporting standards [31,32,38,43,44]. Previous work has impact tested foams in isolation [33,44,45] or covered with thin polypropylene shells [31,32,38,43,44].…”

“…Previous work has impact tested foams in isolation [33,44,45] or covered with thin polypropylene shells [31,32,38,43,44]. Comparisons between auxetic and conventional foams have not been made in more complex multi-material systems, such as helmets.…”

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

“…Auxetic materials have a negative Poisson's ratio (NPR) [15], which could reduce peak forces/accelerations under impacts, giving potential to improve protective equipment [16,17]. From elasticity theory [18], Poisson's ratio (ν) influences the relationship between Young's modulus (E), shear modulus (G) and bulk modulus (K) (Equations (1) and (2)).…”

“…Lower bulk modulus increases volumetric deformation [18], increasing energy absorption under uniaxial compression [16,17]. The effects of higher shear modulus and densification due to lateral material flow under an indentation have not been tested in NPR foams.…”