A crumpled sheet of paper displays an intricate pattern of creases and point-like singular structures, termed d-cones. It is typically assumed that elongated creases form when ridges connecting two d-cones fold beyond the material yielding threshold, and scarring is thus a by-product of the folding dynamics that seek to minimize elastic energy. Here we show that rather than merely being the consequence of folding, plasticity can act as its instigator. We introduce and characterize a different type of crease that is inherently plastic and is formed by the propagation of a single point defect. When a pre-existing d-cone is strained beyond a certain threshold, the singular structure at its apex sharpens abruptly. The resulting focusing of strains yields the material just ahead of the singularity, allowing it to propagate, leaving a furrow-like scar in its wake. We suggest an intuitive fracture analogue to explain the creation of furrows.
Bibliographical noteFunding Information:
This work was supported by ISF grant number 1415/12 and Harvard MRSEC (DMR 14-20570). We are grateful to John Hutchinson, Elisha Moses, Tom Witten, Ariel Amir and Benny Davidovitch for insightful discussions. E.E. gratefully acknowledges the support of the Simons foundation.
© 2015 Macmillan Publishers Limited.