arXiv subjects

Bhanu Prasad Bhowmik

Publications and source records attributed to Bhanu Prasad Bhowmik.

17 recordsLinked to original sources

arXiv2026

Tunable shear thickening in active frictional non-Brownian suspensions

We study tunable shear thickening in active suspensions of non-Brownian, repulsive, frictional grains using particle-based simulation, finding that activity augments the rheology beyond the friction- mediated shear thickening paradigm. Specifically, up to a crossover activity strength, increasing particle self-propulsion drives a viscosity-reducing `dethickening' of the system at large stresses, where the material would otherwise be in a thickened, highly viscous state. Above this crossover activity strength, the system enters a thickening regime. Self-propulsion introduces additional isotropic dynamics to the particles, which compete with the flow-driven formation of frictional contacts. The degree of dethickening can thus be tuned by varying a suitably-defined dimensionless active stress that quantifies this competition. Recognising the parallels between self-propulsion and other contemporary routes to dethickening, we demonstrate that our data, within the dethickening regime, are consistent with a recently proposed universal scaling framework, offering a route to tuning the rheology of dense suspensions. Moreover, using the obtained scaling relation, we infer how the shear-jamming and shear-thickening regimes can be tuned by choosing an appropriate self-propulsion strength, and partially validate these inferences with targeted simulations.

cond-mat.soft↗

arXiv2025

Finite Disorder Critical Point in Brittle-to-Ductile Transition in Amorphous Solids with Aspherical Impurities

Enhancing the mechanical properties of amorphous solids is crucial for material design, with microalloying being a common but not well-understood method. Using extensive molecular dynamics simulations, we investigate the effect of impurity particles on the yielding transition of amorphous solids in the context of brittle-ductile transition with microalloying. Spherical impurities larger than the constitutive particles enhance the systems mechanical stability, leading to a higher yield strain and increased brittleness. Much more potent effects are observed for rod-shaped impurities of the same size as the spherical impurities, with an aspect ratio slightly larger than one, which primarily introduce rotational degrees of freedom into the system. However, as the aspect ratio increases, their rotational degrees of freedom decrease, causing a more brittle yielding with more localized shear band formation. It is remarkable to see how freezing the rotational degrees of freedom can create extremely brittle, yet remarkably stable amorphous solids. Enhancing brittleness through higher concentrations of aspherical impurities presents an intriguing opportunity to explore the ductile-to-brittle transition, which is easily accessible in experiments, particularly in colloidal experiments. Our thorough finite-size scaling analysis has revealed a compelling suggestion of a finite-disorder critical point: a boundary between ductile and brittle behaviors.

cond-mat.soft↗

arXiv2025

Tuning the Viscosity and Jamming Point in Dense Active non-Brownian Suspensions

Using numerical simulations, we study the rheological response of dense non-Brownian suspensions containing active particles. The active particles are modelled as run-and-tumble particles with three controlling parameters: the fraction of active particles in the system, an active force applied to the particles, and a persistence time after which the direction of the active force changes randomly. Our simulations reveal that the presence of activity can reduce the viscosity (by an order of magnitude) by decreasing the number of frictional contacts, which also shifts the jamming point to a higher volume fraction. Moreover, the microscopic structure of force chains in the presence of activity is qualitatively different from that in the passive system, showing reduced anisotropy. We also find that while the presence of activity drives the system away from jamming by preventing the formation of force chains, unjamming an already jammed state by breaking existing force chains requires a higher activity strength. Finally, we propose a new constitutive law to describe the rheology of dense active non-Brownian suspensions.

cond-mat.soft↗

arXiv2025

Finite Disorder Critical Point in the Brittle-to-Ductile Transition of Amorphous Solids in the Presence of Particle Pinning

The mechanical yielding of amorphous solids under external loading can be broadly classified into ductile and brittle types, depending on whether their macroscopic stress response is smooth or abrupt, respectively. Recently, it has been shown that these two regimes, obtained by tuning the degree of annealing of the system, are separated by a critical point at a finite inherent disorder strength. Here, we demonstrate a transition from brittle yielding to ductile yielding by introducing quenched disorder in the form of randomly pinned particles. The well-annealed samples, which exhibit brittle yielding, undergo a transition to increasingly ductile yielding with increasing pinning concentrations while exhibiting an enhanced stress overshoot. Extensive finite size analysis is performed to demonstrate the critical nature of the transition at a finite pinning concentration and the various scaling exponents obtained are found to be in good agreement with the reported values. Finally, we show a direct correspondence with the shear band width and the critical pining concentration to establish a possible connection between inherent disorder strength and quenched disorder strength due to particle pinning.

cond-mat.soft↗

arXiv2024

Unifying homogeneous and inhomogeneous rheology of dense suspensions

The rheology of dense suspensions lacks a universal description due to the involvement of a wide variety of parameters, ranging from the physical properties of solid particles to the nature of the external deformation or applied stress. While the former controls microscopic interactions, spatial variations in the latter induce heterogeneity in the flow, making it difficult to find suitable constitutive laws to describe the rheology in a unified way. For homogeneous driving with a spatially uniform strain rate, the rheology of non-Brownian dense suspensions is well described by the conventional $μ(J)$ rheology. However, this rheology fails in the inhomogeneous case due to non-local effects, where the flow in one region is influenced by the flow in another. Here, motivated by observations from simulation data, we introduce a new dimensionless number, the suspension temperature $Θ_s$, which contains information on local particle velocity fluctuations. We find that $μ(J,Θ_s)$ provides a unified description for both homogeneous and inhomogeneous flows. By employing scaling theory, we identify a set of constitutive laws for dense suspensions of frictional spherical particles and frictionless rod-shaped particles. Combining these scaling relations with the momentum balance equation for our model system, we predict the spatial variation of the relevant dimensionless numbers, the volume fraction $ϕ$, the viscous number $J$, the macroscopic friction coefficient $μ$, and $Θ_s$ solely from the nature of the imposed external driving.

cond-mat.soft↗

arXiv2024

Absorbing-state transitions in particulate systems under spatially varying driving

We study the absorbing state transition in particulate systems under spatially inhomogeneous driving using a modified random organization model. For smoothly varying driving the steady state results map onto the homogeneous absorbing state phase diagram, with the position of the boundary between absorbing and diffusive states being insensitive to the driving wavelength. Here the phenomenology is well-described by a one-dimensional continuum model that we pose. For discontinuously varying driving the position of the absorbing phase boundary and the exponent characterising the fraction of active particles are altered relative to the homogeneous case.

cond-mat.soft↗

arXiv2023

Scaling description of frictionless dense suspensions under inhomogeneous flow

Predicting the rheology of dense suspensions under inhomogeneous flow is crucial in many industrial and geophysical applications, yet the conventional `$μ(J)$' framework is limited to homogeneous conditions in which the shear rate and solids fraction are spatially invariant. To address this shortcoming, we use particle-based simulations of frictionless dense suspensions to derive new constitutive laws that unify the rheological response under both homogeneous and inhomogeneous conditions. By defining a new dimensionless number associated with particle velocity fluctuations and combining it with the viscous number, the macroscopic friction and the solids fraction, we obtain scaling relations that collapse data from homogeneous and inhomogeneous simulations. The relations allow prediction of the steady state velocity, stress and volume fraction fields using only knowledge of the applied driving force.

cond-mat.soft↗

arXiv2022

Creep failure of amorphous solids under tensile stress

Applying constant tensile stress to a piece of amorphous solid results in a slow extension, followed by an eventual rapid mechanical collapse. This "creep" process is of paramount engineering concern, and as such was the subject of study in a variety of materials, for more than a century. Predictive theories for $τ_w$, the expected time of collapse, are lacking, mainly due to its dependence on a bewildering variety of parameters, including temperature, system size, tensile force, but also the detailed microscopic interactions between constituents. The complex dependence of the collapse time on all the parameters is discussed below, using simulations of strip of amorphous material. Different scenarios are observed for ductile and brittle materials, resulting in serious difficulties in creating an all-encompassing theory that could offer safety measures for given conditions. A central aim of this paper is to employ scaling concepts, to achieve data collapse for the probability distribution function (pdf) of $\ln{τ_w}$. The scaling ideas result in a universal function which provides a prediction of the pdf of $\ln{τ_w}$ for out-of-sample systems, from measurements at other values of these parameters. The predictive power of the scaling theory is demonstrated for both ductile and brittle systems. Finally, we present a derivation of universal scaling function for brittle materials. The ductile case appears to be due to a plastic necking instability and is left for future research.

cond-mat.soft↗

arXiv2021

Direct Measurement of Dipoles in Anomalous Elasticity of Amorphous Solids

Recent progress in studying the physics of amorphous solids has revealed that mechanical strains can be strongly screened by the formation of plastic events that are typically quadrupolar in nature. The theory stipulated that gradients in the density of the quadrupoles act as emergent dipole sources, leading to strong screening and to qualitative changes in the mechanical response, as seen for example in the displacement field. In this Letter we firstly offer direct measurements of the dipole field, independently of any theoretical assumptions, and secondly we demonstrate detailed agreement with the recently proposed theory. These two goals are achieved using data from both simulations and experiments. Finally we show how measurements of the dipole fields pinpoint the theory parameters that determine the profile of the displacement field.

cond-mat.dis-nn↗

arXiv2021

Scaling Theory for Wöhler plots in amorphous solids under cyclic forcing

In mechanical engineering Wöhler plots serve to measure the average number of load cycles before materials break, as a function of the maximal stress in each cycle. Although such plots are prevalent in engineering for more than 150 years, their theoretical understanding is lacking. Recently a scaling theory of Wöhler plots in the context of cyclic bending was offered [1]. Here we elaborate further on cyclic bending and extend the considerations to cyclic tensile loads on an amorphous strip of material; the scaling theory applies to both types of cyclic loading equally well. On the basis of atomistic simulations we conclude that the crucial quantities to focus on are the accumulated damage and the average damage per cycle. The dependence of these quantities on the loading determines the statistics of the number of cycles to failure. Finally we consider the probability distribution functions of the number of cycles to failure and demonstrate that the scaling theory allows prediction of these distributions at one value of the forcing amplitude from measurements and another value.

cond-mat.soft↗

arXiv2021

Soft-Pinning: Experimental Validation of Static Correlations in Supercooled Molecular Glass-forming Liquids

Enormous enhancement in the viscosity of a liquid near its glass transition is generally connected to the growing many-body static correlations near the transition, often coined as `amorphous ordering'. Estimating the length scales of such correlations in different glass-forming liquids is highly important to unravel the physics of glass formation. Experiments on molecular glass-forming liquids become pivotal in this scenario as the viscosity grows several folds ($\sim 10^{14}$), simulations or colloidal glass experiments fail to access the long-time scales required. Here we design an experiment to extract the static length scales in molecular liquids using dilute amounts of another large molecule as a pinning site. Results from dielectric relaxation experiments on supercooled glycerol with different pinning concentrations of sorbitol and the simulations on a few model glass-forming liquids with pinning sites indicate the robustness of the proposed method, opening a plethora of opportunity to study the physics of other glass-forming liquids.

cond-mat.soft↗

arXiv2021

Fatigue and Collapse of Cyclically Bent Strip of Amorphous Solid

Fatigue caused by cyclic bending of a piece of material, resulting in its mechanical failure, is a phenomenon that had been studied for ages by engineers and physicists alike. In this Letter we study such fatigue in a strip of athermal amorphous solid. On the basis of atomistic simulations we conclude that the crucial quantity to focus on is the {\em accumulated damage}. Although this quantity exhibits large sample-to-sample fluctuations, its dependence on the loading determines the statistics of the number of cycles to failure. Thus we can provide a scaling theory for the Wöhler plots of mean number of cycles for failure as a function of the loading amplitude.

cond-mat.soft↗

arXiv2020

Thermodynamic Equivalence of Cyclic Shear and Deep Cooling in Glass-Formers

The extreme slowing down associated with glass formation in experiments and in simulations results in serious difficulties to prepare deeply quenched, well annealed, glassy material. Recently, methods to achieve such deep quenching were proposed, including vapor deposition on the experimental side and "Swap Monte Carlo" and oscillatory shearing on the simulation side. The relation between the resulting glasses under different protocols remains unclear. Here we show that oscillatory shear and "Swap Monte Carlo" result in thermodynamically equivalent glasses sharing the same statistical mechanics and similar mechanical responses under external strain.

cond-mat.soft↗

arXiv2019

Particle pinning suppresses spinodal criticality in the shear banding instability

Strained amorphous solids often fail mechanically by creating a shear-band. It had been understood that the shear banding instability is usefully described as crossing a spinodal point (with disorder) in an appropriate thermodynamic description. It remained contested however whether the spinodal is critical (with divergent correlation length) or not. Here we offer evidence for critical spinodal by using particle pinning. For a finite concentration of pinned particles the correlation length is bounded by the average distance between pinned particles, but without pinning it is bounded by the system size.

cond-mat.soft↗

arXiv2018

Effect of pinning on the yielding transition of amorphous solids

Using numerical simulations, we have studied the yielding response, in the athermal quasi static limit, of a model amorphous material having inclusions in the form of randomly pinned particles. We show that, with increasing pinning concentration, the plastic activity becomes more spatially localized, resulting in smaller stress drops, and corresponding increase in the magnitude of strain where yielding occurs. We demonstrate that, unlike the spatially heterogeneous and avalanche led yielding in the case of the unpinned glass, for the case of large pinning concentration, yielding takes place via a spatially homogeneous proliferation of localized events.

cond-mat.soft↗

arXiv2018

Non-Gaussianity of van Hove Function and Dynamic Heterogeneity Length Scale

Non-Gaussian nature of the probability distribution of particles' displacements in the supercooled temperature regime in glass-forming liquids are believed to be one of the major hallmarks of glass transition. It is already been established that this probability distribution which is also known as the van Hove function show universal exponential tail. The origin of such an exponential tail in the distribution function is attributed to the hopping motion of particles observed in the supercooled regime. The non-Gaussian nature can also be explained if one assumes that the system has heterogeneous dynamics in space and time. Thus exponential tail is the manifestation of dynamic heterogeneity. In this work we directly show that non-Gaussanity of the distribution of particles' displacements occur over the dynamic heterogeneity length scale and dynamical behaviour course grained over this length scale becomes homogeneous. We study the non-Gaussianity of van Hove function by systematically coarse graining at different length scale and extract the length scale of dynamic heterogeneity at which the shape of the van Hove function crosses over from non-Gaussian to Gaussian. The obtained dynamic heterogeneity scale is found to be in very good agreement with the scale obtained from other conventional methods.

cond-mat.stat-mech↗

arXiv2016

Understanding Stokes-Einstein Relation in Supercooled Liquids using Random Pinning

Breakdown of Stokes-Einstein relation in supercooled liquids is believed to be one of the hallmarks of glass transition. The phenomena is studied in depth over many years to understand the microscopic mechanism without much success. Recently it was found that violation of Stokes-Einstein relation in supercooled liquids can be tuned very systematically by pinning randomly a set of particles in their equilibrium positions. This observation suggested a possible framework where breakdown of Stokes-Einstein relation in the dynamics of supercooled liquids can be studied with precise control. We have done extensive molecular dynamics simulations to understand this phenomena by analyzing the structure of appropriately defined set of dynamically slow and fast particles clusters. We have shown that the Stokes-Einstein breakdown actually become predominant once the cluster formed by the slow particles percolate the entire system size. Finally we proposed a possible close connection between fractal dimensions of these clusters and the exponents associated with the fractional Stokes-Einstein relation.

cond-mat.stat-mech↗