Crumpled Kirigami

A simple act of crumpling a 2D sheet can make a complex 3D spherical structure that creates a new bulk state with different mechanical properties than the 2D sheet from which it was made. Understanding these structures has challenged scientists for many years. Compared with sheets, crumples have a rigid structure made from long-range structural features such as folds, bends, and ridges and short-range structural features such as D-cones. In our studies, we focused on identifying the most dominant features creating the rigidity of the crumple. We studied crumples made out of different materials (Polydimethylsiloxane-PDMS, Polycarbonate-PC, and Paper) and we changed the topography of those films by adding cuts, with the motivation of disturbing the underlying structural network of long-range features in the crumple. We run simple force experiments under the confocal microscope or an Instron universal test machine to identify any changes due to the added cuts. Our main observation is that adding cuts does very little to the compressibility of the crumpled sheet. Further studies using coarse-grain molecular dynamics show similar behavior. Our simple crushing experiments and simulations strongly suggest that the long-range structural features, and the networks they create during crumpling, are not a dominant part of the problem.