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Elastic avalanches in amorphous solids

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When a sufficiently large stress is applied to amorphous solids (e.g. glasses, foams), these solids deform plastically, i.e. undergo flow at a finite strain rate. In the limit of small strain rates, the corresponding flow can be separated in elastic loading phases followed by stress drops called "avalanches" that dissipate the stored elastic enegy. These avalanches have many analogies to earthquakes, and display similar scale free (power law) statistics. Their properties in the stationanry flow regime have now been extensively characterized, and are largely understood at the level of scaling analysis [see e.g. Nicolas et al, Review of Modern Physics 2018].

In this work, we study the much less characterized situation of a solid which is deformed at very small strains, with a macroscopic behavior that appears to be perfectly elastic and reversible. In fact, even under such conditions, the system undergoes dissipĆ¢tive stress drops which give rise to dissipation, sometimes called "internal friction". We show that the corresponding stress drops also obeys scale free statistics, however with a power law exponent that is different from the one observed in stationnary flow. This exponent reflects th ecomplex geometry of phase space in the vicinity of a local energy minimum. The statistical analysis also reveals that rapidly quenched amorphous solids are typically marginally stable, i.e. that the equilibrium state can be disturbed, in the thermodynamic limit, by infinitesimal perturbations.

View online : Elastic avalanches reveal marginal behaviour in amorphous solids, Baoshuang Shanga, Pengfei Guana, and Jean-Louis Barrat. PNAS december 2019