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 $v_{e}$. 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 $v_{e}$, the interface is stuck to the field profile. As $v_{e}$ 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 $v_{e}$, on the other hand, the interface is macroscopically smooth with a vanishing roughness exponent $\alpha$. 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 $v_e$ is increased. We determine the dynamical ``phase - diagram'' of this system in the $v_e$ - 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

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

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