4,369 research outputs found
Plastic Response of a 2D Amorphous Solid to Quasi-Static Shear : II - Dynamical Noise and Avalanches in a Mean Field Model
We build a minimal, mean-field, model of plasticity of amorphous solids,
based upon a phenomenology of dissipative events derived, in a preceding paper
[A. Lemaitre, C. Caroli, arXiv:0705.0823] from extensive molecular simulations.
It reduces to the dynamics of an ensemble of identical shear transformation
zones interacting via the dynamic noise due to the long ranged elastic fields
induced by zone flips themselves. We find that these ingredients are sufficient
to generate flip avalanches with a power-law scaling with system size,
analogous to that observed in molecular simulations. We further show that the
scaling properties of avalanches sensitively depend on the detailed shape of
the noise spectrum. This points out the importance of developing a realistic
coarse-grained description of elasticity in these systems
Rate-Dependent Avalanche Size in Athermally Sheared Amorphous Solids
We perform an extensive numerical study of avalanche behavior in a 2D LJ
glass at T=0, sheared at finite strain rates . From the finite size
analysis of stress fluctuations and of transverse diffusion we show that
flip-flip correlations remain relevant at all realistic strain rates. We
predict that the avalanche size scales as , with the
space dimension
Ultrafast spherulitic crystal growth as a stress-induced phenomenon specific of fragile glass-formers
We propose a model for the abrupt emergence, below temperatures close to the
glass transition, of the ultra-fast (GC) steady mode of spherulitic crystal
growth in deeply undercooled liquids. We interpret this phenomenon as
controlled by the interplay between the generation of stresses by
crystallization and their partial release by flow in the surrounding amorphous
visco-elastic matrix. Our model is consistent with both the observed ratios
() of fast-to-slow velocities and the fact that fast growth emerges
close to the glass transition. It leads us to conclude that the existence of a
fast growth regime requires both (i) a high fragility of the glassformer; (ii)
the fine sub-structure specific of spherulites. It finally predicts that the
transition is hysteretic, thus allowing for an independent experimental test
Subextensive Scaling in the Athermal, Quasistatic Limit of Amorphous Matter in Plastic Shear Flow
We present the results of numerical simulations of an atomistic system
undergoing plastic shear flow in the athermal, quasistatic limit. The system is
shown to undergo cascades of local rearrangements, associated with quadrupolar
energy fluctuations, which induce system-spanning events organized into lines
of slip oriented along the Bravais axes of the simulation cell. A finite size
scaling analysis reveals subextensive scaling of the energy drops and
participation numbers, linear in the length of the simulation cell, in good
agreement with the observed real-space structure of the plastic events.Comment: 4 pages, 6 figure
Plastic response of a 2D amorphous solid to quasi-static shear : I - Transverse particle diffusion and phenomenology of dissipative events
We perform extensive simulations of a 2D LJ glass subjected to quasi-static
shear deformation at T=0. We analyze the distribution of non-affine
displacements in terms of contributions of plastic, irreversible events, and
elastic, reversible motions. From this, we extract information about
correlations between plastic events and about the elastic non-affine noise.
Moreover, we find that non-affine motion is essentially diffusive, with a
clearly size-dependent diffusion constant. These results, supplemented by close
inspection of the evolving patterns of the non-affine tangent displacement
field, lead us to propose a phenomenology of plasticity in such amorphous
media. It can be schematized in terms of elastic loading and irreversible flips
of small, randomly located shear transformation zones, elastically coupled via
their quadrupolar fields
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