**Particle rearrangement and softening contributions to the nonlinear
mechanical response of glasses**

M Fan and K Zhang and J Schroers and MD Shattuck and CS O'Hern, PHYSICAL
REVIEW E, 96, 032602 (2017).

DOI: 10.1103/PhysRevE.96.032602

Amorphous materials such asmetallic, polymeric, and colloidal glasses
exhibit complex preparation-dependent mechanical response to applied
shear. In particular, glassy soli ds yield, with a mechanical response
that transitions from elastic to plastic, with increasing shear strain.
We perform numerical simulations to investigate the mechanical response
of binary Lennard-Jones glasses undergoing athermal, quasistatic pure
shear as a function of the cooling rate R used to prepare them. The
ensemble-averaged stress versus strain curve resembles
the spatial average in the large size limit, which appears smooth and
displays a putative elastic regime at small strains, a yielding-related
peak in stress at intermediate strain, and a plastic flowregime at large
strains. In contrast, for each glass configuration in the ensemble, the
stress-strain curve sigma(gamma) consists of many short nearly linear
segments that are punctuated by particle-rearrangement-induced rapid
stress drops. To explain the nonlinearity of , we quantify
the shape of the small stress-strain segments and the frequency and size
of the stress drops in each glass configuration. We decompose the stress
loss **i.e., the deviation in the slope of from that at
into the loss from particle rearrangements and the loss
from softening ****i.e., the reduction of the slopes of the linear segments
in sigma(gamma)**, and then compare the two contributions as a function
of R and.. For the current studies, the rearrangement-induced stress
loss is larger than the softening-induced stress loss, however,
softening stress losses increase with decreasing cooling rate. We also
characterize the structure of the potential energy landscape along the
strain direction for glasses prepared with different R, and observe a
dramatic change of the properties of the landscape near the yielding
transition. We then show that the rearrangement-induced energy loss per
strain can serve as an order parameter for the yielding transition,
which sharpens for slow cooling rates and in large systems.

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