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Fig. 1. Representative three-layer Variable Poisson’s Ratio (VPR) metamaterial () illustrated in both undeformed and deformed (compressed) configurations. The VPR behavior is constructed by layering regions with gradually changing void aspect ratios, and thus, gradually changing effective Poisson’s ratio. Inset images illustrate horizontal deformation maps of representative base cells to highlight auxetic behavior.
This and the next image are from:
L. Francesconi, A. Baldi, X. Liang, F. Aymerich and M. Taylor,
“Variable Poisson’s ratio materials for globally stable static and dynamic compression resistance”, Extreme Mechanics Letters, Vol. 26, pp 1-7, January 2019, https://doi.org/10.1016/j.eml.2018.11.001
ABSTRACT: A novel porous mechanical metamaterial with variable Poisson’s ratio (VPR) is proposed for compression and impact applications. Constructed by stacking layers of varying void aspect ratio, VPR structures combine the collapsing penetration resistance of auxetic materials with the lateral expansion of positive Poisson’s ratio (PPR) materials. The concept is analyzed via numerical simulation of both compression and impact loading of VPR structures composed of silicone rubber. In addition, compression testing is performed with deformation maps obtained through digital image correlation. Results indicate that VPR structures, compared with uniform porous PPR structures, are resistant to global buckling instabilities. Moreover, in low-energy impact events, VPR structures respond to the impulse with a comparable force spread over a longer time than uniform PPR structures of the same porosity. At impact energies above approximately 45 J, the considered silicone VPR structures transition to a regime of more sharply peaked force response. At all energies, VPR structures deform more smoothly than their porous PPR counterparts.
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