Effect of Compressive Strain Rate on Auxetic Foam

Abstract

Auxetic foams have previously been shown to have benefits including higher indentation resistance than their conventional counterparts, due to their negative Poisson’s ratio, making them better at resisting penetration by concentrated loads. The Poisson’s ratio and Young’s modulus of auxetic open cell foams have rarely been measured at the high compressive strain rates typical during impacts of energy absorbing material in sporting protective equipment. Auxetic closed cell foams are less common than their open cell counterparts, and only their quasi-static characteristics have been previously reported. It is, therefore, unclear how the Poisson’s ratio of auxetic foam, and associated benefits such as increased indentation resistance shown at low strain rates, would transfer to the high strain rates expected under impact. The aim of this study was to measure the effect of strain rate on the stiffness and Poisson’s ratio of auxetic and conventional foam. Auxetic open cell and closed cell polymer foams were fabricated, then compression tested to ~80% strain at applied rates up to 200 s−1, with Poisson’s ratios obtained from optical full-field strain mapping. Open cell foam quasi-static Poisson’s ratios ranged from −2.0 to 0.4, with a narrower range of −0.1 to 0.3 for closed cell foam. Poisson’s ratios of auxetic foams approximately halved in magnitude between the minimum and maximum strain rates. Open cell foam quasi-static Young’s moduli were between 0.02 and 0.09 MPa, whereas closed cell foams Young’s moduli were ~1 MPa, which is like foam in protective equipment. The Young’s moduli of the auxetic foams approximately doubled at the highest applied strain rate of 200 s−1.

Developments on auxetic closed cell foam pressure vessel fabrications

“…The unconverted foam compressive strain data was nonlinear, with a plateau region between 5% and 10% compression (figure 8(a))-as expected [40,48,54,60,61]. As with Poisson's ratio data, mean values for Young's moduli are presented-with direction dependent values in supplementary figures S7 and S8.…”

3D Printing Auxetic Architectures for Hypertrophic Scar Therapy

“…[ 7 ] Also, the effect of the compressive strain rate on the stiffness and PR of auxetic foam has been discussed. [ 8 ] Analyses, such as topology optimization, homogenization and finite element analysis (FEA), have been explored in an attempt to enhance the auxetic architectures for optimal shock absorption. [ 4a,9 ]…”

“…[7] Also, the effect of the compressive strain rate on the stiffness and PR of auxetic foam has been discussed. [8] Analyses, such as topology optimization, homogenization and finite element analysis (FEA), have been explored in an attempt to enhance the auxetic architectures for optimal shock absorption. [4a,9] Apart from the exceptional impact resistance effect, the synclastic (dome-shaped) curvature of auxetic materials is a phenomenal characteristic that not only enhances the formability of the material itself, but also the fit and conformity to 3D body forms and even accommodates the expansion and contraction of the body during posture changes.…”

Finite deformation and fractional order viscoelasticity of an auxetic foam

“…The experimental behavior of various auxetic foam materials has been extensively studied. The compressive stress/strain behavior has been studied by Bezazi and Scarpa (2007), Pastorino et al (2007), Lisiecki et al (2014), Duncan et al (2021), and the cyclic compressive stress/strain behavior by Casavola et al (2021), Bezazi and Scarpa (2007), Zhang et al (2020), Duncan et al (2016), Opreni et al (2020). Due to their negative Poisson’s ratio behavior, it is important to examine the Poisson behavior of auxetic foams as strain changes.…”

“…Due to their negative Poisson’s ratio behavior, it is important to examine the Poisson behavior of auxetic foams as strain changes. Bezazi and Scarpa (2007), Zhang et al (2020), Duncan et al (2016), Pastorino et al (2007), Duncan et al (2021) have tested the Poisson’s ratio under compressive strain while Zhang et al (2020), Scarpa et al (2005), Duncan et al (2021) have tested the Poisson’s ratio under tension. Additional work investigating the stress/strain behavior of open-cell polyurethane (PU) auxetic foams under tension has been completed (Casavola et al, 2021; Scarpa et al, 2005; Zhang et al, 2020).…”