Auteur/autrice : Benoît Roman

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

Here is the link to the article Elastocapillary adhesion of a soft cap on a rigid sphere

The capillary adhesion of soft shells on spheres of different curvature gives rise to a family of complex adhesion patterns.

The article was first published on 22 Jan 2020
Soft Matter, 2020,16, 1961-1966
https://doi.org/10.1039/C9SM02057H

Inflatable structures are flat and foldable when empty and both lightweight and stiff when pressurized and deployed. They are easy to manufacture by fusing 2 inextensible sheets together along a defined pattern of lines. However, the prediction of their deployed shape remains a mathematical challenge, which results from the coupling of geometrical constraints and the strongly nonlinear and asymmetric mechanical properties of their composing material: thin sheets are very stiff on extensional loads, while they easily shrink by buckling or wrinkling when compressed. We discuss the outline shape, local cross-section, and state of stress of any curvilinear open path. We provide a reverse model to design any desired curved 2-dimensional shape from initially flat tubes.

See our article in PNAS and the Supplementary Information.