Écoulement Et Dynamique de Matériaux Amorphes Forcés Et Actifs
Author | : Magali Le Goff |
Publisher | : |
Total Pages | : 0 |
Release | : 2021 |
ISBN-10 | : OCLC:1285131460 |
ISBN-13 | : |
Rating | : 4/5 (60 Downloads) |
Book excerpt: Soft glassy materials far from their glass transition (low temperature, high density) exhibit divergent relaxation timescales and behave essentially as solids in absence of driving or biological activity.In this thesis, we investigate the dynamics, rheology and large scale organization of various types of (athermal) soft amorphous materials resulting either from an externally imposed driving (shear or vibration), from a local activity, or both.The main question behind the different projects constituting this thesis is: how do distinct sources of mechanical noise affect the fluidization and large scale organization of soft amorphous materials and how to account for it in coarse-grained descriptions?To this aim, we use a multi-scale modeling approach, from microscopic simulations to continuum modeling, with a main focus on mesoscale elasto-plastic models.The first topic of this thesis concerns shear localization in the flow of soft amorphous materials. We first consider the case of inertial dynamics at the microscopic scale as a rate-weakening mechanisms and show, using a continuum model, that permanent shear bands observed in particle-based simulations can be explained in terms of softening due to kinetic heating of the system under shear, with a shear rate dependent kinetic temperature.In a second part, we study how permanent shear bands are affected by an external (rate-independent) source of noise leading to the random activation of plastic rearrangements.We show, using a mesoscale elasto-plastic model with two different models of noise, that an increasing external noise leads to vanishing shear bands, and that the transition from heterogeneous to homogeneous flow can be interpreted as a nonequilibrium critical point. Our findings suggest that the critical exponents associated with this transition do not depend on the details of the activation dynamics for the noise, and are also consistent with recent experimental results on vibrated granular media.Fluidization by a rate-independent noise is an ubiquitous phenomenon, observed not only in vibrated granular media, but also in active or biological systems, where the noise if of active origin.In a third part, we study how active sources of noise resulting from the active deformation of particles can induce a fluidization of the system.Using inputs from microscopic simulations, we build a tensorial mesoscale elasto-plastic model for the dynamics of actively deforming particles.We show that this model reproduces the discontinuous fluidization transition observed in particle-based simulations and shares analogy with inert amorphous systems driven with an oscillatory shear protocol.In a last part, motivated by experiments in the lab, we consider a vertex-based model to study oscillations of the migration velocity of cells in confined epithelial tissues. We find that a feedback mechanism between the cell self-propulsion direction and velocity is required to observe oscillations, and that the type of oscillation observed depends upon the confinement length as reported in experiments.