Finite curved creases in infinite isometric sheets

TL;DR

This paper models the crescent-shaped vertices in crumpled sheets as finite curved creases in isometric sheets, providing geometric insights into stress focusing and crescent size scaling.

Contribution

It introduces a geometric approach to model crescent vertices as finite curved creases, capturing their unique features and linking surface profile to crease-line geometry.

Findings

Finite curved creases are fully realizable within isometric sheets.

Derived testable relations between creases and surrounding sheet.

Discussed implications for crescent size scaling in crumpled sheets.

Abstract

Geometric stress focusing, e.g. in a crumpled sheet, creates point-like vertices that terminate in a characteristic local crescent shape. The observed scaling of the size of this crescent is an open question in the stress focusing of elastic thin sheets. According to experiments and simulations, this size depends on the outer dimension of the sheet, but intuition and rudimentary energy balance indicate it should only depend on the sheet thickness. We address this discrepancy by modeling the observed crescent with a more geometric approach, where we treat the crescent as a curved crease in an isometric sheet. Although curved creases have already been studied extensively, the crescent in a crumpled sheet has its own unique features: the material crescent terminates within the material, and the material extent is indefinitely larger than the extent of the crescent. These features together with the general constraints of isometry lead to constraints linking the surface profile to the crease-line geometry. We construct several examples obeying these constraints, showing finite curved creases are fully realizable. This approach has some particular advantages over previous analyses, as we are able to describe the entire material without having to exclude the region around the sharp crescent. Finally, we deduce testable relations between the crease and the surrounding sheet, and discuss some of the implications of our approach with regards to the scaling of the crescent size.