Auxetic behavior and unusual shear resistance of crumpled materials: Opportunities for programming the nonlinear responses of crumpled mechanical metamaterials

Abstract

Crumpled systems (CSs) can be used as building blocks of mechanical metamaterials with low sensitivity to defects. But to exploit the potential of CSs for novel applications, extensive understanding of the physics of these systems is needed and, so far, the shear response of CSs has not been studied. Here we study the shear response of CSs via short/large amplitude oscillatory shear (SAOS/LAOS) while investigating the effect of several parameters. The training of crumpled paper reduced long-range correlations and resulted in an increase of the shear modulus with compaction, not observed for untrained paper. The presence of stacked layers parallel to the shear direction, in contrast to those positioned perpendicularly, resulted in lower shear storage modulus and increased energy dissipation through layers sliding. Reducing the surface friction allowed for easier internal rearrangements during shear deformations. In general, the shear resistance increases less with the increasing level of compaction than the compaction stiffness. However, it can be tuned by friction between the layers and their orientation. The estimated Poisson’s ratio of CSs reveals their auxetic nature. Our results pave the way to better understand the full mechanical response of CSs and tune their desired properties for practical applications.