Unifying two apparently different tearing instabilities (PRL)

We have shown that the spiraling path (when a cone is pushed through a brittle sheet) and the oscillatory crack path (when a blunt object tears through a brittle sheet) both result from the same instability.

Cutting a brittle thin sheet with a blunt object leaves an oscillating crack that seemingly violates the principle of local symmetry for fracture. We experimentally find that at a critical value of a well chosen control parameter the straight propagation is unstable and leads to an oscillatory pattern whose amplitude and wavelength grow by increasing the control parameter. We propose a simple model that unifies this instability with a related problem, namely that of a perforated sheet, where through a similar bifurcation a series of radial cracks spontaneously spiral around each other. We argue that both patterns originate from the same instability.

See the article here in Physical Review Letters

Nature of Crack Path Instabilities in Thin Sheets Cut by Blunt Objects

Eugenio Hamm, Iryna Sivak, and Benoît Roman
Phys. Rev. Lett. 124, 174101 – Published 29 April 2020