Ref HAL: hal-02880587_v1
Ref Arxiv: 1911.12951
DOI: 10.1103/PhysRevLett.124.225502
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Résumé:

We perform molecular dynamics simulations to investigate the effect of a glass preparation on its yielding transition under oscillatory shear. We use swap Monte Carlo to investigate a broad range of glass stabilities from poorly annealed to highly stable systems. We observe a qualitative change in the nature of yielding, which evolves from ductile to brittle as glass stability increases. Our results disentangle the relative role of mechanical and thermal annealing on the mechanical properties of amorphous solids, which is relevant for various experimental situations from the rheology of soft materials to fatigue failure in metallic glasses.

Ref HAL: hal-02738157_v1
Ref Arxiv: 1910.11168
DOI: 10.1103/PhysRevLett.124.225901
WoS: 000537199500009
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9 Citations
Résumé:

Amorphous solids exhibit quasi-universal low-temperature anomalies whose origin has been as-cribed to localized tunneling defects. Using an advanced Monte Carlo procedure, we createin silicoglasses spanning from hyperquenched to ultrastable glasses. Using a multidimensional path-finding protocol, we locate tunneling defects with energy splittings smaller than kBTQ, with TQ the temperature below which quantum effects are relevant (TQ≈1 K in most experiments). We find thatas the stability of a glass increases, its energy landscape as well as the manner in which it is probed tend to deplete the density of tunneling defects, as observed in recent experiments. We explore thereal-space nature of tunneling defects, and find that they are mostly localized to a few atoms, butare occasionally dramatically delocalized

Ref HAL: hal-02591059_v1
Ref Arxiv: 1904.07359
DOI: 10.1103/PhysRevLett.124.058001
WoS: 000510750600010
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2 Citations
Résumé:

We show that non-Brownian suspensions of repulsive spheres below jamming display a slow relaxational dynamics with a characteristic time scale that diverges at jamming. This slow time scale is fully encoded in the structure of the unjammed packing and can be readily measured via the vibrational density of states. We show that the corresponding dynamic critical exponent is the same for randomly generated and sheared packings. Our results show that a wide variety of physical situations, from suspension rheology to algorithmic studies of the jamming transition are controlled by a unique diverging timescale, with a universal critical exponent.

Ref HAL: hal-02569130_v1
Ref Arxiv: 1912.06416
DOI: 10.1103/PhysRevMaterials.4.025603
WoS: 000515722500007
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Résumé:

Amorphous solids display a ductile to brittle transition as the kinetic stability of the quiescent glass is increased, which leads to a material failure controlled by the sudden emergence of a macroscopic shear band in quasi-static protocols. We numerically study how finite deformation rates influence ductile and brittle yielding behaviors using model glasses in two and three spatial dimensions. We find that a finite shear rate systematically enhances the stress overshoot of poorly-annealed systems, without necessarily producing shear bands. For well-annealed systems, the non-equilibrium discontinuous yielding transition is smeared out by finite shear rates and it is accompanied by the emergence of multiple shear bands that have been also reported in metallic glass experiments. We show that the typical size of the bands and the distance between them increases algebraically with the inverse shear rate. We provide a dynamic scaling argument for the corresponding lengthscale, based on the competition between the deformation rate and the propagation time of the shear bands.

Ref HAL: hal-02445176_v1
Ref Arxiv: 1811.03171
DOI: 10.21468/SciPostPhys.7.6.077
WoS: 000505803200006
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4 Citations
Résumé:

We study the equilibrium statistical properties of the potential energy landscape of several glass models in a temperature regime so far inaccessible to computer simulations. We show that unstable modes of the stationary points undergo a localization transition in real space close to the mode-coupling crossover temperature determined from the dynamics. The concentration of localized unstable modes found at low temperature is a non-universal, finite dimensional feature not captured by mean-field glass theory. Our analysis reconciles, and considerably expands, previous conflicting numerical results and provides a characteristic temperature for glassy dynamics that unambiguously locates the mode-coupling crossover.

Ref HAL: hal-02358674_v1
PMID 31704936
DOI: 10.1038/s41467-019-13010-x
WoS: 000495393400002
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6 Citations

Ref HAL: hal-02358763_v1
Ref Arxiv: 1903.09108
DOI: 10.1103/PhysRevLett.123.175501
WoS: WOS:000491998300008
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1 Citation
Résumé:

Ultrastable vapor-deposited glasses display uncommon material properties. Most remarkably, upon heating they are believed to melt via a liquid front that originates at the free surface and propagates over a mesoscopic crossover length, before crossing over to bulk melting. We combine swap Monte Carlo with molecular dynamics simulations to prepare and melt isotropic amorphous films of unprecedendtly high kinetic stability. We are able to directly observe both bulk and front melting, and the crossover between them. We measure the front velocity over a broad range of conditions, and a crossover length scale that grows to nearly $400$ particle diameters in the regime accessible to simulations. Our results disentangle the relative roles of kinetic stability and vapor deposition in the physical properties of stable glasses.

Commentaires: 7 pages, 6 figures; accepted for publication in Phys. Rev. Lett. Réf Journal: Phys. Rev. Lett. 123, 175501 (2019)