Star-shaped crack pattern of broken windows
Nicolas Vandenberghe, Romain Vermorel, and Emmanuel Villermaux
Accepted
Broken thin brittle plates like windows and windshields are ubiquitous in our environment. When impacted locally, they typically present a pattern of cracks extending radially outwards from the impact point. We study the variation of the pattern of cracks by performing controlled transverse impacts on brittle plates over a broad range of impact speed, plate thickness and material properties, and we establish from experiments a global scaling law for the number of radial cracks incorporating all these parameters. A model based on Griffith's theory of fracture combining plate bending elastic energy and fracture energy accounts for our observations. These findings indicate how the post-mortem shape of broken samples are related to material properties and impact parameters, a procedure relevant to forensic science, archaeology or astrophysics.