1,273 research outputs found
Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel
In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of
post-irradiated austenitic stainless steel in Light Water Reactor (LWR)
environment, reliable predictions of intergranular stresses are required.
Finite elements simulations have been performed on realistic polycrystalline
aggregate with a recently proposed physically-based crystal plasticity
constitutive equations validated for neutron-irradiated austenitic stainless
steel. Intergranular normal stress probability density functions are found with
respect to plastic strain and irradiation level, for uniaxial loading
conditions. In addition, plastic slip activity jumps at grain boundaries are
also presented. Intergranular normal stress distributions describe, from a
statistical point of view, the potential increase of intergranular stress with
respect to the macroscopic stress due to grain-grain interactions. The
distributions are shown to be well described by a master curve once rescaled by
the macroscopic stress, in the range of irradiation level and strain considered
in this study. The upper tail of this master curve is shown to be insensitive
to free surface effect, which is relevant for IGSC
Continuum limit of amorphous elastic bodies (III): Three dimensional systems
Extending recent numerical studies on two dimensional amorphous bodies, we
characterize the approach of elastic continuum limit in three dimensional
(weakly polydisperse) Lennard-Jones systems. While performing a systematic
finite-size analysis (for two different quench protocols) we investigate the
non-affine displacement field under external strain, the linear response to an
external delta force and the low-frequency harmonic eigenmodes and their
density distribution. Qualitatively similar behavior is found as in two
dimensions. We demonstrate that the classical elasticity description breaks
down below an intermediate length scale , which in our system is
approximately 23 molecular sizes. This length characterizes the correlations of
the non-affine displacement field, the self-averaging of external noise with
distance from the source and gives the lower wave length bound for the
applicability of the classical eigenfrequency calculations. We trace back the
"Boson-peak" of the density of eigenfrequencies (obtained from the velocity
auto-correlation function) to the inhomogeneities on wave lengths smaller than
.Comment: 27 pages, 11 figures, submitted to Phys. Rev.
Particle displacements in the elastic deformation of amorphous materials: local fluctuations vs. non-affine field
We study the local disorder in the deformation of amorphous materials by
decomposing the particle displacements into a continuous, inhomogeneous field
and the corresponding fluctuations. We compare these fields to the commonly
used non-affine displacements in an elastically deformed 2D Lennard-Jones
glass. Unlike the non-affine field, the fluctuations are very localized, and
exhibit a much smaller (and system size independent) correlation length, on the
order of a particle diameter, supporting the applicability of the notion of
local "defects" to such materials. We propose a scalar "noise" field to
characterize the fluctuations, as an additional field for extended continuum
models, e.g., to describe the localized irreversible events observed during
plastic deformation.Comment: Minor corrections to match the published versio
Vibrations of amorphous, nanometric structures: When does continuum theory apply?
Structures involving solid particles of nanometric dimensions play an
increasingly important role in material sciences. These structures are often
characterized through the vibrational properties of their constituent
particles, which can be probed by spectroscopic methods. Interpretation of such
experimental data requires an extension of continuum elasticity theory down to
increasingly small scales. Using numerical simulation and exact diagonalization
for simple models, we show that continuum elasticity, applied to disordered
system, actually breaks down below a length scale of typically 30 to 50
molecular sizes. This length scale is likely related to the one which is
generally invoked to explain the peculiar vibrational properties of glassy
systems.Comment: 4 pages, 5 figures, LATEX, Europhysics Letters accepte
On the study of local stress rearrangements during quasistatic plastic shear of a model glass: do local stress components contain enough information?
We present a numerical study of the mechanical response of a 2D Lennard-Jones
amorphous solid under steady quasistatic and athermal shear. We focus here on
the evolution of local stress components. While the local stress is usually
taken as an order parameter in the description of the rheological behaviour of
complex fluids, and for plasticity in glasses, we show here that the knowledge
of local stresses is not sufficient for a complete description of the plastic
behaviour of our system. The distribution of local stresses can be
approximately described as resulting from the sum of localized quadrupolar
events with an exponential distribution of amplitudes. However, we show that
the position of the center of the quadrupoles is not related to any special
evolution of the local stress, but must be described by another variable
Inhomogeneous elastic response of silica glass
Using large scale molecular dynamics simulations we investigate the
properties of the {\em non-affine} displacement field induced by macroscopic
uniaxial deformation of amorphous silica,a strong glass according to Angell's
classification. We demonstrate the existence of a length scale
characterizing the correlations of this field (corresponding to a volume of
about 1000 atoms), and compare its structure to the one observed in a standard
fragile model glass. The "Boson-peak'' anomaly of the density of states can be
traced back in both cases to elastic inhomogeneities on wavelengths smaller
than , where classical continuum elasticity becomes simply unapplicable
Storage Device Sizing for a Hybrid Railway Traction System by Means of Bicausal Bond Graphs
In this paper, the application of bicausal bond graphs for system design in electrical engineering is emphasized. In particular, it is shown how this approach is very useful for model inversion and parameter dimensioning. To illustrate these issues, a hybrid railway traction device is considered as a case study. The synthesis of a storage device (a supercapacitor) included in this system is then discussed
Continuum limit of amorphous elastic bodies: A finite-size study of low frequency harmonic vibrations
The approach of the elastic continuum limit in small amorphous bodies formed
by weakly polydisperse Lennard-Jones beads is investigated in a systematic
finite-size study. We show that classical continuum elasticity breaks down when
the wavelength of the sollicitation is smaller than a characteristic length of
approximately 30 molecular sizes. Due to this surprisingly large effect
ensembles containing up to N=40,000 particles have been required in two
dimensions to yield a convincing match with the classical continuum predictions
for the eigenfrequency spectrum of disk-shaped aggregates and periodic bulk
systems. The existence of an effective length scale \xi is confirmed by the
analysis of the (non-gaussian) noisy part of the low frequency vibrational
eigenmodes. Moreover, we relate it to the {\em non-affine} part of the
displacement fields under imposed elongation and shear. Similar correlations
(vortices) are indeed observed on distances up to \xi~30 particle sizes.Comment: 28 pages, 13 figures, 3 table
Plastic Response of a 2D Lennard-Jones amorphous solid: Detailed analysis of the local rearrangements at very slow strain-rate
We analyze in details the atomistic response of a model amorphous material
submitted to plastic shear in the athermal, quasistatic limit. After a linear
stress-strain behavior, the system undergoes a noisy plastic flow. We show that
the plastic flow is spatially heterogeneous. Two kinds of plastic events occur
in the system: quadrupolar localized rearrangements, and shear bands. The
analysis of the individual motion of a particle shows also two regimes: a
hyper-diffusive regime followed by a diffusive regime, even at zero
temperature
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