PIECING together details of a car accident or crime scene could become a bit easier thanks to star-like cracks in glassy substances. These characteristic patterns can reveal the speed of the objects that made them.
It has long been known that different materials require different amounts of energy to crack. But until now few studies have examined the patterns of cracks left behind to trace back details about the impact.
Nicolas Vandenberghe and colleagues at in France used an air gun to fire small metal cylinders at glass plates at increasingly higher speeds, reaching 432 kilometres per hour. A high-speed camera filmed each shot, and the team counted the radial cracks formed by the impact. 鈥淎s surprising as it might be, that had not been done before,鈥� says team member Emmanuel Villermaux.
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The team found a unique relationship between the number of cracks and the projectile鈥檚 speed. They were able to use this to develop a simple equation that can tell how fast an object was travelling, based on the type of material it hit ().
, a materials scientist at Lawrence Berkeley National Laboratory in California, says the work is a useful analysis. 鈥淔or forensics, you could use this to find the energy of a bullet.鈥� The work could also reveal how fast a car was moving just before an accident, by looking for cracks in the windshield created by stones kicked up from the road.
This article appeared in print under the headline 鈥淪tarburst fractures can help forensic experts crack a case鈥�
