Inhomogeneous shear flows in soft jammed materials with tunable attractive forces

Chaudhuri, Pinaki; Berthier, Ludovic; Bocquet, Lydéric

doi:10.1103/physreve.85.021503

Cited by 70 publications

(80 citation statements)

References 68 publications

(123 reference statements)

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“…The strain localization is a result of the appearance of a linear array of a sub-extensive number of localized plastic events [3,19,25,26]. In Fig 4(b) we plot the displacement field that results from such an array of localized plastic events that are represented by an Eshelby inclusion [3,4,18,19] (compare to the displacement field observed in the simulation in Fig 1(d)). The most obvious feature of this field is the convective pattern which appears in between the inclusions.…”

Section: Figmentioning

confidence: 91%

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Onset of irreversibility and chaos in amorphous solids under periodic shear

2013

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An important aspect of the physics of amorphous solids is the onset of irreversible behavior usually associated with yield. Here we study amorphous solids under periodic shear using quasi-static molecular dynamics simulations and observe a transition from reversible to irreversible deformation at a critical strain amplitude. We find that for small strain amplitudes the system exhibits a noisy but repetitive limit-cycle, similar to return point memory [1]. However, for large strain amplitudes the behavior becomes chaotic (shows sensitivity to initial conditions) and thus irreversible. We show that the chaotic behavior is a result of the shear band instabilities that arise for large strains and the convective displacement fields they create.Amorphous solids such as plastics, window glass and amorphous metals are an important and ubiquitous form of matter. Industrial processing of such materials commonly involves plastic deformation (for example plastic forming). While a microscopic mechanism of plastic deformation in these materials was identified [2-4] the collective behavior on the mesoscale is still being debated. Current theoretical understanding of amorphous solids includes mainly mean-field statistical mechanics theories that are based on the assumption that the behavior is stochastic. Therefore, the dynamics is described in terms of probability distributions which follow the evolution of localized particle rearrangements exhibiting a transition from jammed to flowing behavior [5][6][7][8]. Recent experiments and simulations on superconductor vortices, dilute colloidal dispersions and loosely packed granular materials show that these materials undergo a transition from reversible to irreversible diffusive behavior by varying the strength of an oscillatory external field [9][10][11][12][13][14][15][16][17]. In this work we study highly condensed amorphous solids (well above the jamming transition) under oscillatory shear and show that for small strain amplitudes these systems evolve into periodic limit cycles where particles change their positions during the cycle but keep following the same trajectories for consecutive cycles. These reversible rearrangements result in energy fluctuations, which for small strains are completely repetitive which resembles return point memory [1]. Above a critical strain amplitude, the system does not settle into a limit cycle and the motion is chaotic with a positive maximal Lyapunov exponent. This allows us to define a yield point, which can be difficult to determine from a stress strain curve (green curve Fig 1). We explain the onset of chaotic behavior as a result of a convective displacement fields which result from strain localization which generally appears during yield in amorphous solids [3,18,19]. Identifying and understanding the underlying mechanism of chaotic behavior opens the possibility of a quantitative understanding of structural changes that occur in these systems and their relation to the dynamics.We perform molecular dynamics simulations of a system of N po...

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Section: Figmentioning

confidence: 91%

“…In figure 1(a) we see that after the critical point the stress-strain curve is not smooth anymore but is jugged with large avalanche-like events which result from strain localization [3,18,19]. The strain localization is a result of the appearance of a linear array of a sub-extensive number of localized plastic events [3,19,25,26].…”

Section: Figmentioning

confidence: 98%

Onset of irreversibility and chaos in amorphous solids under periodic shear

2013

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“…The disks interact via the following potential, which can be considered to be a model for cohesive grains or attractive emulsions [18,19]:…”

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confidence: 99%

“…Theoretical models suggest that non-monotonic flow curves can occur due to long-lived local fluidizations when the post-rupture restructuring takes a very long time [12][13][14]. However, experiments and numerical simulations have shown that for φ > φ J , no such instabilities occur in the flow curve for either repulsive or attractive systems [15][16][17][18]. The question now arises whether for φ < φ J , a short-ranged attraction which introduces a new lengthscale for structure formation leads to longer restoration timescales and if this is indeed the origin of a shear banding instability.…”

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confidence: 99%

Impact of Attractive Interactions on the Rheology of Dense Athermal Particles

2014

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Using numerical simulations, the rheological response of an athermal assembly of soft particles with tunable attractive interactions is studied in the vicinity of jamming. At small attractions, a fragile solid develops and a finite yield stress is measured. Moreover, the measured flow curves have unstable regimes, which lead to persistent shearbanding. These features are rationalized by establishing a link between the rheology and the inter-particle connectivity, which also provides a minimal model to describe the flow curves.PACS numbers: 83.10. Rs,83.60.Wc,66.20.Cy In nature, soft disordered solids occur in different forms (eg. gels, emulsions, colloids, foams, grains etc) across a wide range of packing fractions φ, which is made possible by the tuning of particle interactions. The flow properties of these soft materials have been harnessed for various applications, e.g. in the food or the chemical industry. Thus, understanding the role of particle interactions and the corresponding mechanisms which lead to observed rheological behaviour is an important recurrent theme.For non-Brownian suspensions of frictionless repulsive spheres, it is observed that ramping up the packing fraction results in the occurrence of jamming at φ = φ J [1, 2]. The rheological signature of the onset of jamming is the development of a finite yield stress at φ J [3]. For Brownian suspensions of such particles, it has been shown that a yield stress exists at φ < φ J , due to the presence of thermal vibrations [4]. A similar systematic investigation of how the jamming paradigm is changing upon the introduction of attractive particle interactions is still missing. It is known that at smaller φ, such systems do exhibit finite yield stress [5,9,19,24]; but, a quantitative bridge with the jamming scenario needs to be developed.Such studies are also needed since shear-banding, the phenomenon of spatially inhomogeneous flows observed in many soft yield-stress fluids [6, 7], has often been attributed to attractive interactions [8,9]. In general, persistent occurrence of shear-bands has been linked to nonmontonic constitutive laws leading to flow instabilities [6, 10] (e.g. in micelles [11]). It is not known how interparticle attractions could result in such instabilities.Conceptually, one can imagine the steady flowing state to be a regime where there is a continuous competition between the rupturing induced by shear and processes that try to restore local structure. Theoretical models suggest that non-monotonic flow curves can occur due to long-lived local fluidizations when the post-rupture restructuring takes a very long time [12][13][14]. However, experiments and numerical simulations have shown that for φ > φ J , no such instabilities occur in the flow curve for either repulsive or attractive systems [15][16][17][18]. The question now arises whether for φ < φ J , a short-ranged attraction which introduces a new lengthscale for structure formation leads to longer restoration timescales and if this is indeed the origin of a shear banding ...

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“…In addition, granular vortices may be related to the nonlocal behaviour of granular flows [11,12]. Unlike classical fluids, the local viscosity of granular materials depends on the level of shear rate and stresses in the surrounding media.…”

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confidence: 99%

A circulation-based method for detecting vortices in granular materials

2015

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Dense granular flows exhibit large clusters of grains rotating in correlated fashions. We present a method to identify and quantify such granular vortices, based on the circulation of velocity fluctuations around closed curves. Here, the method is applied on physical experiments of twodimensional granular flows in the Stadium Shear Device geometry. Results illustrate how the method is capable to capture the positions, sizes, velocities and life-times of individual vortices. The method should be useful for many purposes, including: (1) complementing existing ways for defining typical correlation lengths in granular systems; (2) studying the kinematics behind the superior efficiency of granular systems to transfer of mass, heat and momentum when compared with other fluids; and (3) characterising vortices in other particulate fluid systems such as suspensions, emulsions and foams, which exhibit similar velocity patterns.

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Inhomogeneous shear flows in soft jammed materials with tunable attractive forces

Cited by 70 publications

References 68 publications

Onset of irreversibility and chaos in amorphous solids under periodic shear

Onset of irreversibility and chaos in amorphous solids under periodic shear

Impact of Attractive Interactions on the Rheology of Dense Athermal Particles

A circulation-based method for detecting vortices in granular materials

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