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Cornell University
LASSP -  Laboratory of Atomic and Solid State Physics

Cornell Laboratory for Atomic and Solid State Physics

Shekhawat, Sethna & Zapperi develop unified theory of fracture

Clean materials like glasses break abruptly. Complex materials like bones and seashells develop many small damaged regions (microcracks) before breaking. These microcracks happen with a broad, scale-invariant distribution of sizes reminiscent of earthquakes and crackling noise. But this can not be due to a phase transition, because as the system size goes to infinity the strength of disordered materials goes to zero. ‘Smaller is stronger’ really means ‘large is weak’ here — a rare, large damaged zone will cause an infinite system to fail at arbitrarily low stress – hence nothing else breaks. Ashivni Shekhawat, Stefano Zapperi, and James Sethna show that these precursor fracture events are due to ‘finite-size criticality’. At short length scales, all materials are sensitive to disorder; at long length-scales all behave like glass. They describe the smooth, finite-size crossover between these two regimes quantitatively using universal scaling functions and their leading corrections. Bones, seashells, and modern composite materials are tough because of this distributed damage — which we finally now understand clearly.

Read more in the Chronicle and in the viewpoint by Elisabeth Bouchaud.

Different types of crack formation predicted to occur in a brittle solid when the size of the system or the amount of disorder is varied.