Forced tearing of ductile and brittle thin sheets

TL;DR

This paper investigates the different crack morphologies that occur when forcing a rigid object through thin sheets of ductile and brittle materials, using experiments, simulations, and theories to understand the transition between regimes.

Contribution

It introduces a unified framework describing crack morphologies and transitions in thin sheets under different forcing directions, supported by laws and phase diagrams.

Findings

Oscillatory cracks in brittle sheets

Concertina folds in ductile sheets

Phase diagram of tearing regimes

Abstract

Tearing a thin sheet by forcing a rigid object through it leads to complex crack morphologies; a single oscillatory crack arises when a tool is driven laterally through a brittle sheet, while two diverging cracks and a series of concertina-like folds forms when a tool is forced laterally through a ductile sheet. On the other hand, forcing an object perpendicularly through the sheet leads to radial petal-like tears in both ductile and brittle materials. To understand these different regimes we use a combination of experiments, simulations and simple theories. In particular, we describe the transition from brittle oscillatory tearing via a single crack to ductile concertina tearing with two tears by deriving laws that describe the crack paths and wavelength of the concertina folds and provide a simple phase diagram for the morphologies in terms of the material properties of the sheet and the relative size of the tool.