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R. Mari

Publications and source records attributed to R. Mari.

5 recordsLinked to original sources
arXiv2026

Avalanches in the Random Organization Model with long-range interactions

Oscillatory sheared suspensions, when observed stroboscopically, exhibit a reversible-irreversible transition as a function of the strain amplitude, which is a kind of absorbing phase transition. So far studies of this transition focused on global quantities, e.g. quantifying the irreversibility on one side of the transition or the time to reach a reversible state on the other side. Here, motivated by the kin depinning transition, we focus on the intermittent dynamics near the transition. We perform simulations of a modified Random Organization Model (ROM), a minimal particle model which we recently adapted to take into account the generic presence of long-range interactions mediated by the fluid, taking the power-law-decay exponent $\alpha$ as an additional control parameter of the model. We show that at the absorbing phase transition, this model displays power-law-distributed avalanches. We characterize the avalanche statistics in terms of avalanche size, duration and number of particles involved, and we determine the associated exponents. By varying the exponent $\alpha$, the fractal dimension of avalanches crosses space dimension $d$, inducing a qualitative change of the spatial structure of avalanches, from compact avalanches when interactions have a short range, to sparse avalanches when interactions are long-ranged. Finally, we characterize the clusters within the avalanches, which we also find power-law distributed.

cond-mat.soft↗
arXiv2023

Microscopically grounded constitutive model for dense suspensions of soft particles below jamming

We derive from particle-level dynamics a constitutive model describing the rheology of two-dimensional dense soft suspensions below the jamming transition, in a regime where hydrodynamic interactions between particles are screened. Based on a statistical description of particle dynamics, we obtain through a set of physically plausible approximations a non-linear tensorial evolution equation for the deviatoric part of the stress tensor, involving the strain-rate and vorticity tensors. This tensorial evolution equation involves singular terms usually not taken into account in phenomenological constitutive models, which most often assume a regular expansion in terms of the stress tensor. All coefficients appearing in the equation have known expressions in terms of the microscopic parameters of the model. The predictions of this microscopically grounded constitutive model have several qualitative features that are specific to the rheology of soft suspensions measured in experiments or simulations. The model shows a typical behavior of polymeric visco-elastic materials, such as normal stress differences quadratic in the shear rate $\dot\gamma$, as well as typical behaviors of suspensions of stiff particles, such as a particle pressure linear in $\dot\gamma$ and a zero-shear viscosity diverging at the jamming transition. The model also predicts a sharper shear thinning than other visco-elastic models at small shear rates, in qualitative agreement with experimental observations. Furthermore the shear thinning follows a critical scaling close to the jamming transition.

cond-mat.soft↗
arXiv2013

Mechanical response of an inclined frictional granular layer approaching unjamming

We present an orthotropic elastic analysis of frictional granular layers under gravity by studying their stress response to a localized overload at the layer surface for several substrate tilt angles. The distance to the unjamming transition is controlled by the tilt angle α with respect to the critical angle α_c. We find that the shear modulus of the system decreases with α, but reaches a finite value as αtends to α_c. We also analyze the vibration modes of the system and show that the soft modes play an increasing, though not crucial, role approaching the transition.

cond-mat.soft↗
arXiv2009

Jamming versus Glass Transitions

Recent ideas based on the properties of assemblies of frictionless particles in mechanical equilibrium provide a perspective of amorphous systems different from that offered by the traditional approach originating in liquid theory. The relation, if any, between these two points of view, and the relevance of the former to the glass phase, has been difficult to ascertain. In this paper we introduce a model for which both theories apply strictly: it exhibits on the one hand an ideal glass transition and on the other `jamming' features (fragility, soft modes) virtually identical to that of real systems. This allows us to disentangle the different contents and domains of applicability of the two physical phenomena.

cond-mat.stat-mech↗