Fig. 4
(Reproduced with permission from Grima et al. [38]. Copyright 2016 Wiley-VCH)
a Typical images of a crumpled sheet of paper at different levels of applied strain and b typical images of a graphene sheet having 3.0% defects at different levels of applied strain. Note that both systems undergo a de-wrinkling process so as to assume a more planar conformation resulting in an in-plane negative Poisson’s ratio