Radial cracks in perforated thin sheets

International audienceWhen a rigid cone is slowly pushed through a thin elastic sheet, the material breaks, exhibiting a network of cracks expanding in the radial direction. Experiments conducted with aluminum sheets show that the number of cracks is selected at the beginning of the perforation process and then remains stable. A simple model predicts the number of cracks as the result of a competition between the elastic energy stored in the sheet, and the energy dissipated during crack extension. We also evidence the subtle rearrangements of randomly distributed cracks into uniform radial patterns with fewer cracks. In that respect, this study exemplifies how relaxation mechanisms in fragmenting solids can attenuate the influence of defects in the material