8,164 research outputs found
Towards the ab initio based theory of the phase transformations in iron and steel
Despite of the appearance of numerous new materials, the iron based alloys
and steels continue to play an essential role in modern technology. The
properties of a steel are determined by its structural state (ferrite,
cementite, pearlite, bainite, martensite, and their combination) that is formed
under thermal treatment as a result of the shear lattice reconstruction "gamma"
(fcc) -> "alpha" (bcc) and carbon diffusion redistribution. We present a review
on a recent progress in the development of a quantitative theory of the phase
transformations and microstructure formation in steel that is based on an ab
initio parameterization of the Ginzburg-Landau free energy functional. The
results of computer modeling describe the regular change of transformation
scenario under cooling from ferritic (nucleation and diffusion-controlled
growth of the "alpha" phase to martensitic (the shear lattice instability
"gamma" -> "alpha"). It has been shown that the increase in short-range
magnetic order with decreasing the temperature plays a key role in the change
of transformation scenarios. Phase-field modeling in the framework of a
discussed approach demonstrates the typical transformation patterns
Correlation and shear bands in a plastically deformed granular medium
Recent experiments (Le Bouil et al., Phys. Rev. Lett., 2014, 112, 246001)
have analyzed the statistics of local deformation in a granular solid
undergoing plastic deformation. Experiments report strongly anisotropic
correlation between events, with a characteristic angle that was interpreted
using elasticity theory and the concept of Eshelby transformations with
dilation; interestingly, the shear bands that characterize macroscopic failure
occur at an angle that is different from the one observed in microscopic
correlations. Here, we interpret this behavior using a mesoscale elastoplastic
model of solid flow that incorporates a local Mohr-Coulomb failure criterion.
We show that the angle observed in the microscopic correlations can be
understood by combining the elastic interactions associated with Eshelby
transformation with the local failure criterion. At large strains, we also
induce permanent shear bands at an angle that is different from the one
observed in the correlation pattern. We interpret this angle as the one that
leads to the maximal instability of slip lines
Solid-fluid dynamics of yield-stress fluids
On the example of two-phase continua experiencing stress induced solid-fluid
phase transitions we explore the use of the Euler structure in the formulation
of the governing equations. The Euler structure guarantees that solutions of
the time evolution equations possessing it are compatible with mechanics and
with thermodynamics. The former compatibility means that the equations are
local conservation laws of the Godunov type and the latter compatibility means
that the entropy does not decrease during the time evolution. In numerical
illustrations, in which the one-dimensional Riemann problem is explored, we
require that the Euler structure is also preserved in the discretization.Comment: 51 pages, 7 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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