arXiv subjects

Pinaki Chaudhuri

Publications and source records attributed to Pinaki Chaudhuri.

At least 19 recordsLinked to original sources

arXiv2026

Self-organization and memory formation in two-dimensional jammed deformable matter under cyclic compression

We study the athermal mechanical response of deformable ring assemblies to quasistatic compression. Beyond jamming, further densification induces buckling of rings, resulting in macroscopic mechanical softening. Under cyclic compression, monodisperse systems anneal toward a nearly reversible path passing through an ordered state, whereas polydisperse systems converge to stable, hysteretic limit cycles. These limit cycles encode a robust memory of the training history that is retained even under subsequent overdriving. We show that macroscopic hysteresis in the disordered packings originates from directionally asymmetric non-affine deformations at the microscale while keeping contact network largely intact. Our findings demonstrate how particle deformability governs collective self-organization and memory formation in jammed soft matter.

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arXiv2026

The Jammed Phase of Infinitely Persistent Active Matter

We study an extreme active matter system, which is essentially a dense assembly of athermal, soft and infinitely persistent active particles. Using extensive numerical simulations we obtain jammed configurations of this system in two dimensions and probe the stability of such structures under increasing active forcing magnitude. We show that the critical active forcing magnitude for the jammed phase to yield scales with virial pressure as $f_c\sim p^\alpha$, with $\alpha=1.17$, describing the yielding line. Using a Laplacian framework, we redistribute the active forces into a modified contact force network. By analysing the statistics of these redistributed forces, we obtain a very robust scaling law consistent with the passive limit, not just near the unjamming line, but in the entire jammed active phase. The probability distribution of the magnitude of the contact force deviates from the power-law form found in passive systems for values smaller than the active force. Moreover, within the jammed phase, the system displays elastic, plastic, and yielding events with increasing active forcing. This active plasticity appears abruptly and can not be captured by the continuous softening of the Hessian spectrum. However, we demonstrate that the Hessian still retains the ability to predict relaxation times. These results clarify how activity modifies force distributions and leads to deformation, plasticity and yielding in dense, jammed, infinitely persistent active matter.

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arXiv2025

Glassy dynamics in two-dimensional ring polymers: size versus stiffness polydispersity

Soft glassy materials often consist of deformable objects. Here, we use a two-dimensional assembly of semi-flexible ring polymers as a model system to investigate how polydispersity in particle stiffness or size influences the onset of glassy dynamics. In simulations at fixed polydispersity 30%, we find that stiffness dispersity drives most rings into elongated conformations at high densities, leading to orientationally ordered structures that cause dynamical slowing down. In contrast, size dispersity generates a bimodal population: small rings remain circular and act as rigid inclusions, while large rings elongate, producing frustration that delays arrest. Real-space maps of bond relaxation reveal strikingly different pathways of dynamical heterogeneity, with long-lived domains persisting under stiffness dispersity but rapidly percolating relaxation under size dispersity. Moreover, local correlations between ring shape, orientational order, and mobility show that stiffness dispersity produces dynamics that are strongly structure-sensitive, whereas size dispersity activates motion from both circular and elongated populations. By linking microscopic deformability to emergent glassy dynamics, this study identifies how the nature of polydispersity controls the relaxation pathways of soft glasses.

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arXiv2025

Activity-driven sorting, approach to criticality and turbulent flows in dense persistent active fluids

We show that dense active fluids comprising interacting particles with persistent self-propulsion are driven to a non-equilibrium steady state consisting of co-moving particles with co-aligned active forces. This velocity and force sorting appears to be associated with a critical state where the length scales associated with spatial correlations of the velocity and the propulsive force grow with system size. At large system sizes, these growing velocity domains are accompanied by the appearance of dynamic macroscopic voids in the steady state, associated with large density fluctuations. The dynamics of the macroscopic voids drives a new kind of turbulent state.

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arXiv2025

Cascade at local yield strain for silica and metallic glass

We report observations of unusal \emph{first} plastic events in silica and metallic glasses in the shear startup regime at applied strain two orders of magnitude smaller than yield strain. The (non-Affine) particle displacement field during these events have complex real space structure with multiple disconnected cores of high displacement appearing at the \emph{same} applied strain under athermal quasistatic simple shear deformation, and identified by a ``cell based cluster analysis'' method. By monitoring the stress relaxation during the first plastic event by Langevin dynamics simulation, we directly show the cascade nature of these events. Thus these first plastic events are reminiscent of avalanches in the post-yielding steady state, but unlike the steady state avalanches, we show that these events are not system spanning. To understand the nature of these events, we tune three factors that are known to affect brittleness of a glass. These are (i) sample preparation history, (ii) inter-particle interactions and (iii) rigidity of the background matrix applying a ``soft matrix'' probe recently developed by some of us. In each case we show that such first plastic events are more probable in more ductile glasses. Our observations are consistent with the picture that more ductile materials are softer, implying that understanding the role of softness may be a promising route to develop microscopic quantifiers of brittleness and thus clarifying the physical origin of brittle-to-ductile transition.

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arXiv2025

Influence of active breathing on rheology and jamming of amorphous solids: insights from microscopic and mesoscale analysis

We study the flow behavior and unjamming transition in dense assemblies of actively deforming particles that periodically change size, a process that we refer to as breathing. Using extensive molecular dynamics simulations and a complementary mesoscale elasto-plastic model, we explore how this internal activity influences plasticity and rheology. At low amplitudes of breathing, the system remains jammed and displays localized, reversible rearrangements. As the amplitude of the breathing increases beyond a critical threshold, the system undergoes an activity-induced fluidization marked by a surge in plastic events and a drop in yield stress. The flow curve analysis reveals a transition from yield-stress behavior to Newtonian flow at high activity. The mesoscale model captures these trends and provides insight into the role of stress redistribution due to local active deformations. Our findings highlight the potential of internal active driving to tune the mechanical state of amorphous materials without external forcing.

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arXiv2025

Aging of ring polymeric topological glass formers via thermal quench

We investigate the dynamical response of glass-forming systems composed of topologically constrained ring polymers subjected to an instantaneous thermal quench, employing large-scale molecular dynamics simulations. We demonstrate that the onset of glassiness depends on polymer stiffness, with increased rigidity enhancing configurational constraints and delaying structural relaxation. In the glassy regime, the system exhibits hallmark aging characteristics, as evidenced by two-time correlation functions, namely the mean square displacement and self-intermediate scattering function, which display a clear dependence on the waiting time following the thermal quench. The extracted relaxation timescale ($\tau_\alpha$) follows an approximate simple aging scenario with waiting time ($t_w$), described by $\tau_\alpha \sim t_w^b$, where $0.8 < b < 0.93$. Finally, we analyze the threading of rings during the thermal quench, demonstrating that both increased and persistent threading correlate with the emergence of glassiness. Moreover, the threading persistence timescale exhibits a strong correlation with the structural relaxation timescale. Our study thus provides a comprehensive view of structural relaxation and aging in dense ring polymer systems, highlighting the critical roles of topological constraints and polymer stiffness in governing non-equilibrium glassy dynamics.

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arXiv2025

Athermal creep deformation of ultrastable amorphous solids

We numerically investigate the athermal creep deformation of amorphous materials having a wide range of stability. The imposed shear stress serves as the control parameter, allowing us to examine the time-dependent transient response through both the macroscopic strain and microscopic observables. Least stable samples exhibit monotonicity in the transient strain rate versus time, while more stable samples display a pronounced non-monotonic S-shaped curve, corresponding to failure by sharp shear band formation. We identify a diverging timescale associated with the fluidization process and extract the corresponding critical exponents. Our results are compared with predictions from existing scaling theories relevant to soft matter systems. The numerical findings for stable, brittle-like materials represent a challenge for theoretical descriptions. We monitor the microscopic initiation of shear bands during creep responses. Our study encompasses creep deformation across a variety of materials ranging from ductile soft matter to brittle metallic and oxide glasses, all within the same numerical framework.

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arXiv2024

Cooperative motion in equilibrium phases across two-dimension melting in pure and disordered systems

We uncover the dynamics of particles with Gaussian core interactions across melting in pure and disordered two-dimensional (2D) systems. Intriguing signatures of cooperative motion of particles in string-like paths are found at low temperatures. Such a motion, while common to glasses and supercooled liquids, are realized here in traditional equilibrium phases, including in pure systems. We explore the interplay of such motion and impurities and report their repercussions on spatiotemporal correlations. In particular, cooperative motion seems to cause a departure from the diffusive dynamics, causing slow relaxation.

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arXiv2024

Two-dimensional squishy glass: yielding under oscillatory shear

The yielding response to an imposed oscillatory shear is investigated for a model two-dimensional dense glass composed of bidisperse, deformable polymer rings, with the ring stiffness being the control parameter. In the quiescent glassy state, the more flexible rings exhibit a broader spectrum of shape fluctuations, which becomes increasingly constrained with increasing ring stiffness. Under shear, the highly packed rings yield, i.e. the thermal assembly looses rigidity, with the threshold yield strain increasing significantly with decreasing ring stiffness. Further, the rings display significant deviations in their shape compared to their unsheared counterparts. This study provides insights into the interplay between shape changes and translational rearrangements under shear, thus contributing to the understanding of yielding transition in densely packed, deformable polymer systems.

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arXiv2024

Universal stress correlations in crystalline and amorphous packings

We present a universal characterization of stress correlations in athermal systems, across crystalline to amorphous packings. Via numerical analysis of static configurations of particles interacting through harmonic as well as Lennard-Jones potentials, for a variety of preparation protocols and ranges of microscopic disorder, we show that the properties of the stress correlations at large lengthscales are surprisingly universal across all situations, independent of structural correlations, or the correlations in orientational order. In the near-crystalline limit, we present exact results for the stress correlations for both models, which work surprisingly well at large lengthscales, even in the amorphous phase. Finally, we study the differences in stress fluctuations across the amorphization transition, where stress correlations reveal the loss of periodicity in the structure at short lengthscales with increasing disorder.

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arXiv2023

The effect of disorder on phases across two-dimensional thermal melting

We study melting in a two-dimensional system of classical particles with Gaussian-core interactions in disordered environments. The pure system validates the conventional two-step melting with a hexatic phase intervening between the solid and the liquid. This picture is modified in the presence of pinning impurities. A random distribution of pinning centers forces a hexatic-like low temperature phase that transits into a liquid at a single melting temperature $T^{\rm RP}_{\rm m}$. In contrast, pinning centers located at randomly chosen sites of a perfect crystal anchors a solid at low temperatures which undergoes a direct transition to the liquid at $T^{\rm CP}_{\rm m}$. Thus, the two-step melting is lost in either cases of disorder. We discuss the characteristics of melting depending on the nature of the impurities.

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arXiv2023

Yielding in amorphous solids reveals an age-dependent intrinsic lengthscale

Understanding how amorphous solids yield under shear is central to predicting material failure, yet prescribing reliable local yielding criteria remains a fundamental challenge. Here, through a mesoscale analysis of localized yielding, we reveal an intrinsic length scale (\zeta) that governs local failure, and demonstrate that \zeta grows with the age of the system. The age dependence shows up not only in the features of the distribution of local yield stress but also in the pseudogap exponent \theta, which provides a measure of marginal stability of the amorphous solids. These insights are made possible by a new method, termed the soft matrix approach, that allows local regions of an amorphous solid to yield within a minimally constrained, elastically coupled environment. By overcoming key limitations of earlier techniques, our approach provides a robust platform for probing failure mechanisms, particularly in soft disordered materials and paves the way for improved elastoplastic modeling of disordered solids.

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arXiv2023

Athermal quasistatic cavitation in amorphous solids: effect of random pinning

Amorphous solids are known to fail catastrophically via fracture, wherein cavitation at nano-metric scales is known to play a significant role. Micro-alloying via inclusions is often used as a means to increase the fracture toughness of amorphous solids. Modeling such inclusions as randomly pinned particles that move only affinely and do not participate in plastic relaxation, we study how the pinning influences the process of cavitation-driven fracture in an amorphous solid. Using extensive numerical simulations and probing in the athermal quasistatic limit, we show that just by pinning a very small fraction of particles, the tensile strength is increased and also the cavitation is delayed. Further, the cavitation that is expected to be spatially heterogeneous becomes spatially homogeneous by forming a large number of small cavities instead of a dominant cavity.

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arXiv2023

Onset of glassiness in two-dimensional ring polymers: interplay of stiffness and crowding

The effect of ring stiffness and pressure on the glassy dynamics of a thermal assembly of two-dimensional ring polymers is investigated using extensive coarse-grained molecular dynamics simulations. In all cases, dynamical slowing down is observed with increasing pressure and thereby a phase space for equilibrium dynamics is identified in the plane of obtained monomer density and ring stiffness. When the rings are highly flexible, i.e. low ring stiffness, glassiness sets in via crowding of crumpled polymers which take a globular form. In contrast, at large ring stiffness, when the rings tend to have large asphericity under compaction, we observe the emergence of local domains having orientational ordering, at high pressures. Thus, our simulations highlight how varying the deformability of rings leads to contrasting mechanisms in driving the system towards the glassy regime.

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arXiv2023

Bidisperse ring polymers: topological glass to stacking

Via large-scale molecular dynamics simulations, we observe the melting of a topological glass of stiff ring polymers by incorporating flexible ring polymers, along an isobaric path. As more flexible ring polymers are introduced, cluster glass-like structures emerge in the stiffer ring polymers with reduced orthogonal threading. This eventually evolves to a stacked columnar structure at an increased fraction of flexible ring polymers. Depletion interactions between the stiff and flexible rings drive the stacking, contingent on the disparity in flexibility in the ring polymer mixture.

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arXiv2023

Cavitation instabilities in amorphous solids via secondary mechanical perturbations

Amorphous solids are known to fail catastrophically and in some situations, nano-scaled cavities are believed to play a significant role in the failure. In a recent work, using numerical simulations, we have shown the correspondence between cavitation under uniform expansion of amorphous solids and the yielding under shear. In this study, we probe the stability of spatially-homogeneous states sampled from expansion trajectories to alternate modes of driving, viz. macroscopic cyclic shear or local random deformation via activity. We find that, under cyclic shear and activity, the cavitation instabilities can occur in expanded states at much higher densities than under pure uniform-expansion, and the shift in density is determined by the magnitude of the secondary deformation. We also show that barriers to cavitation on the energy landscape are much smaller for cyclic-shear and activity than seen under expansion. Further, we also analyse the spatial manifestation of cavitation and investigate whether large scale irreversible plasticity can set in due to the combination of expansion and the secondary deformation. Overall, our study reveals the interplay between expansion and other deformation modes leading to cavitation instabilities and the existence of abundant relaxation pathways for such processes.

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arXiv2023

Creep response of athermal amorphous solids under imposed shear stress

Yield stress materials fail when the imposed stress crosses a critical threshold. A well-known dynamical response to the applied stress is the phenomenon of creep where the cumulative deformation grows sublinearly with time, prior to failure or arrest. Using extensive molecular dynamics simulations, we study such response for a model amorphous system, in the athermal limit, and probe how the annealing history of the initial state determines the observed behaviour to an applied shear stress. Further, we analyze the microscopic dynamics in the vicinity of the yield threshold, using large systems, and characterize the spatiotemporal signatures towards arrest or flow, at different scales.

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