161 research outputs found
Mechanical Failure of a Small and Confined Solid
Starting from a commensurate triangular thin solid strip, confined within two
hard structureless walls, a stretch along its length introduces a rectangular
distortion. Beyond a critical strain the solid fails through nucleation of
"smectic"-like bands. We show using computer simulations and simple density
functional based arguments, how a solid-smectic transition mediates the
failure. Further, we show that the critical strain introducing failure is {\em
inversely} proportional to the channel width i.e. thinner strips are stronger!Comment: 6 pages, 7 figures, to be published in Indian Journal of Physics (in
press) as a Conference proceeding of CMDAYS-0
Profile driven interfaces in 1 + 1 dimensions : periodic steady states, dynamical melting and detachment
We study the steady state structure and dynamics of a 2-d Ising interface
placed in an inhomogeneous external field with a sigmoidal profile which moves
with velocity . In the strong coupling limit the problem maps onto an
assymmetric exclusion process involving motion of particles in 1-d with
position dependent right and left jump probabilities. For small , the
interface is stuck to the field profile. As increases the profile
detaches from the interface. At the transition point(and beyond), the
interfacial structure and dynamics is characterized by KPZ exponents. For small
, on the other hand, the interface is macroscopically smooth with a
vanishing roughness exponent . The interfacial structure is periodic
with a periodicity which depends on the orientation of the interface. For a
fixed orientation this periodic structure ``melts'' as is increased. We
determine the dynamical ``phase - diagram'' of this system in the -
orientation plane.Comment: 11 pages, 6 figures, To appear in Physica A as conference proceedings
of Statphys - Kolkata I
Arrested States of Solids
Solids produced as a result of a fast quench across a freezing or a
structural transition get stuck in long-lived metastable configurations of
distinct morphology, sensitively dependent on the processing history. {\it
Martensites} are particularly well studied examples of nonequilibrium
solid-solid transformations. Since there are some excellent reviews on the
subject, we shall, in this brief article, mainly present a summary of our work
on the nonequilibrium statistical mechanics of Martensites.Comment: 4 figs (3 embedded eps and 1 'slide.gif' separate), review written
for Current Scienc
Driven Disordered Polymorphic Solids: Phases and Phase Transitions, Dynamical Coexistence and Peak Effect Anomalies
We study a model for the depinning and driven steady state phases of a solid
tuned across a polymorphic phase transition between ground states of triangular
and square symmetry. These include pinned states which may have dominantly
triangular or square correlations, a plastically flowing liquid-like phase, a
moving phase with hexatic correlations, flowing triangular and square states
and a dynamic coexistence regime characterized by the complex interconversion
of locally square and triangular regions. We locate these phases in a dynamical
phase diagram. We demonstrate that the apparent power-law orientational
correlations we obtain in our moving hexatic phase arise from circularly
averaging an orientational correlation function with qualitatively different
behaviour in the longitudinal (drive) and transverse directions. The
intermediate coexistence regime exhibits several novel properties, including
substantial enhancement in the current noise, an unusual power-law spectrum of
current fluctuations and striking metastability effects. This noise arises from
the fluctuations of the interface separating locally square and triangular
ordered regions. We demonstrate the breakdown of effective ``shaking
temperature'' treatments in the coexistence regime by showing that such shaking
temperatures are non-monotonic functions of the drive in this regime. Finally
we discuss the relevance of these simulations to the anomalous behaviour seen
in the peak effect regime of vortex lines in the disordered mixed phase of
type-II superconductors. We propose that this anomalous behavior is directly
linked to the behavior exhibited in our simulations in the dynamical
coexistence regime, thus suggesting a possible solution to the problem of the
origin of peak effect anomalies.Comment: 22 pages, double column, higher quality figures available from
author
Effect of loading behaviour on compressional property of needle-punched nonwoven fabric
An attempt has been made to understand the effect of different testing parameters on compressional behaviour of needle-punched nonwoven fabric. These parameters are repeated compression-recovery cycles (0-200 kPa), ultimate load (50, 100 and 200 kPa), duration after loading or unloading (up to 6 min with 200 kPa), rate of deformation (1, 5, 10, 15, 20 and 25 mm/min) and testing principles (constant rate of loading or compression). It is found that most of the changes in the compressional properties take place in the first and second compression cycles. In all the cycles, compression parameter (α) and recovery parameter (β) of polypropylene and jute-polypropylene blended fabrics are higher than jute fabric. There is no effect of ultimate compressional pressures selected in this experiment on different compressional parameters. Type of testing principle also affects the extent of compressibility and recovery. As the rate of deformation increases, α, β and energy loss decrease initially and then remain unaltered. When compressional pressure is applied on needle-punched fabric, there is an instantaneous compression and after that thickness loss increases with time in diminishing rate. The thickness loss stabilizes after reaching to maximum which is 55-60% for jute and wet jute, 83% for jute/polypropylene and 92% for polypropylene. Recovery from compression also follows the similar trend. These information will be useful in the real situations where different magnitude and nature of compressional load is applied on needle-punched nonwoven fabrics
Stress relaxation in a perfect nanocrystal by coherent ejection of lattice layers
We show that a small crystal trapped within a potential well and in contact
with its own fluid, responds to large compressive stresses by a novel mechanism
-- the transfer of complete lattice layers across the solid-fluid interface.
Further, when the solid is impacted by a momentum impulse set up in the fluid,
a coherently ejected lattice layer carries away a definite quantity of energy
and momentum, resulting in a sharp peak in the calculated phonon absorption
spectrum. Apart from its relevance to studies of stability and failure of small
sized solids, such coherent nanospallation may be used to make atomic wires or
monolayer films.Comment: 4 pages, 4 figures, published version, changed conten
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