Formation of Fracture Patterns in Brittle Materials Explained by Physics, Math and Special Gels

Researchers have long wondered about the origin of delicate criss-cross facetted patterns that are usually found on the surfaces of broken material. Typical crack speeds in glass effortlessly surpass a kilometer per second, and broken surface features could be smaller than a millimeter.

Since the formation of surface structure exists for just a tiny fraction of a second, the processes producing these patterns have been a relatively significant mystery.

This photograph shows a typical facetted fracture surface formed by the fracture of a brittle gel. (Credit: Hebrew University of Jerusalem)

There is currently a way around this problem. Replacing hard glass with soft but brittle gels allows it to slow down the cracks that lead to precipitating fractures to mere meters per second. This innovative technique has allowed researchers Itamar Kolvin, Gil Cohen and Prof. Jay Fineberg, at the Hebrew University of Jerusalem’s Racah Institute of Physics, to explore the complex physical processes that happen during fracture in microscopic detail and also in real time.

Their work provide new evidence on how broken surface patterns are developed. Surface facets bounded by steps are produced because of a special “topological” arrangement of the crack that cannot simply be undone, just as how it is not possible for a knot along a string to be unraveled without pulling the whole length of the string via it.

The surface developed by a crack is increased by these “crack knots”, thus developing a new venue for dissipating the energy needed for material failure, and therefore making materials that are harder to break.

The complex surfaces that are commonly formed on any fractured object have never been entirely understood, while a crack could form perfectly flat, mirror-like fracture surfaces (and sometimes does), generally complex facetted surfaces are the rule, even though they require much more energy to form. This study illuminates both how such beautiful and intricate patterns emerge in the fracture process, and why the crack cannot divest itself of them once they are formed.

Prof. Jay Fineberg, Hebrew University of Jerusalem’s Racah Institute of Physics

This process that is physically important is capable of providing an aesthetic example of how mathematics and physics intertwine to produce intricate and often unanticipated beauty. The research has been published in Nature Materials.

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