![]() ![]() “Why not think that the fracture processes are also equivalent?” “It seemed that the topographic features of metals and glass were not so different,” says Christian Marlière of Montpellier University in France. That prompted some to wonder whether the ways in which glass and metal break are really so different after all. Using an atomic force microscope (AFM), researchers examined fractured glass at the nanometer scale and found rough, metal-like surfaces. In recent years, though, researchers have looked more closely at broken glass and noticed that its fracture surface is rougher than they had previously thought. Small damage cavities form, grow, and coalesce to advance the crack.Īt the millimeter and micrometer scales, the difference between glass’s smooth fracture surface and metal’s rough one is clear. Over the course of an hour, a crack propagates through a sample of glass. Video courtesy of Christian Marliere, Montpellier Univ. These cavities grow and coalesce to propagate the crack, a process which leads to rough, uneven fracture surfaces. In contrast, ductile fractures occur because stress causes pockets of empty space called damage cavities to form ahead of the crack tip. This process would produce sharp crack tips and smooth fracture surfaces. Researchers have traditionally thought that cracks in brittle materials grow because applied stress causes atomic bonds to stretch and pull apart at the tip of the crack. Brittle materials like glass can’t bend, and so they break more easily. Ductile fracture occurs in metals, which can bend before they shatter. Researchers generally categorize fracture modes into two classes. The research may help explain some of the fracture properties of glass, and may someday lead to stronger versions of the material. But research published in the 21 February print issue of PRL suggests that glass does in fact break like a metal–at least at the nanometer scale. If you dropped a wineglass, you’d expect it to shatter, not skitter across the floor like a silver goblet would. (See video below.) This process was previously thought to apply only to ductile fracture, which occurs in metals. As a crack propagates through glass, nanometer-scale regions of damage start small (top), grow (middle), and coalesce (bottom), to advance the crack tip.
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