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An investigation into the intruder dynamics of dry dimensionless, frictionless discs in bidispersed, disordered systems is carried out using computer simulations. The velocity of an intruder particle driven under constant force is used as a tool to determine scaling of velocity as a function of packing pressure. Using these velocity for a range of pressures, $4 \times 10^{-7}\leq P \leq 4 \times 10^{-2}$. A universal scaling relation is proposed and plotted. The force required to cause the packing to yield to the driven intruder is determined and plotted as function of pressure. Power law exponents were extracted for the yielding force vs. the pressure. The extracted values were used to study the micro-rheology of the intruder particle. Grain scale characteristics are used to infer global elastic modulus properties.

The increasing use of engineered nanoparticles such as silver nanoparticles (AgNPs) has focused more attention on the transport of nanoparticles in natural and engineered systems. Despite a substantial number of studies on the transport of nanoparticles in groundwater flow conditions, other conditions such as those in granular media filtration in water treatment plant have not been fully explored. This study was designed to investigate the transport of AgNPs in granular media filtration with a relatively high filtration velocity (~2 m/hr) and a low influent AgNP concentration (~100 [mu]g/L). Effects of several physical and chemical parameters on the transport and attachment of AgNPs were examined, focusing on the colloidal filtration theory and particle-particle interaction, respectively. Regarding the transport of AgNPs, four physical parameters (filter depth, filtration velocity, filter media size, and AgNP size) were varied at a fixed chemical condition. Positively charged branched polyethylenimine (BPEI) capped AgNPs were chosen to examine the transport of AgNPs under electrostatically favorable attachment conditions. The effects of filter depth, filtration velocity, and filter media size on transport of AgNPs were adequately described by the well-known colloidal filtration model. However, deviation from the model prediction was apparent as the AgNP size became smaller, implying a possible variation of nanoparticle properties in the smaller size such as 10 nm. In the AgNP attachment study, negatively charged citrate- and polyvinylpyrrolidone (PVP)-capped AgNPs were employed to examine the chemical effects on particle (AgNP)-particle (filter media) interaction. When the ionic strength and ion type in the background water were varied, the attachment of citrate AgNPs followed the DLVO theory. Ca- or Mg-citrate complexation was found to lead to charge neutralization, resulting in a greater AgNP deposition onto the filter media. However, PVP AgNPs were only marginally affected by the electrostatic effect, demonstrating a stronger stabilizing effect by PVP than citrate. When natural organic matter (NOM) was introduced in the background water, the deviation from the DLVO theory was considered primarily due to the steric interaction by NOM coating onto particles. Different amounts of AgNP deposition for different types of NOM suggest the variation of steric effects according to the molecular weight of NOM. The deposition of humic acid-coated AgNPs was similar regardless of the capping agent, indicating the possible displacement of the capping agent by NOM. The electrostatic and steric interactions affected the detachment of AgNPs as well as the attachment of AgNPs. The amount of detachment depended on the depth and width of the secondary energy minimum. Also, the detachment was enhanced with NOM coating, probably due to a weak attachment by the steric effect. However, the hydrodynamic force employed in this study was insufficient to yield a remarkable detachment. Overall, the retention profile was a relatively vertical line (i.e., equal deposition with depth) when the AgNP aggregation was prevented by the electrostatic or steric repulsion, implying homogeneous AgNP capture throughout the filter bed. On the other hand, ripening (the capture of particles by attraction to previously retained particles) was favored at the top of the filter bed when the AgNP aggregation was allowable. / text

The objective of this research is to discover principles of ambulatory locomotion on homogeneous and heterogeneous granular substrates and create models of animal and robot interaction within such environments. Since interaction with natural substrates is too complicated to model, we take a robophysics approach – we create a terrain generation system where properties of heterogeneous multi-component substrates can be systematically varied to emulate a wide range of natural terrain properties such as compaction, orientation, obstacle shape/size/distribution, and obstacle mobility within the substrate. A schematic of the proposed system is discussed in detail in the body of this dissertation. Control of such substrates will allow for the systematic exploration of parameters of substrate properties, particularly substrate stiffness and heterogeneities. With this terrain creation system, we systematically explore locomotor strategies of simplified laboratory robots when traversing over different terrain properties. A key feature of this proposed work is the ability to generate general interaction models of locomotor appendages with such complex substrates. These models will aid in the design and control of future robots with morphologies and control strategies that allow for effective navigation on a large diversity of terrains, expanding the scope of terramechanics from large tracked and treaded vehicles on homogeneous ground to arbitrarily shaped and actuated locomotors moving on complex heterogeneous terrestrial substrates.

An interest in vehicle efficiency improvement drives a need for research in the field of light metal alloys. Current industrially-available technologies do not include warm-forming of metal alloy sheet materials. The obstacles to the technology may be potentially overcome with granular media, which could be used as an alternative force transfer medium. However, some granular material properties like force chain formation require further investigation before forming technology using granular media may be developed. Throughout the course of this study, a direct shear cell instrument was designed and fabricated. This instrument was used to measure the basic mechanical properties of granular media. A 3D CAD model of the direct shear cell instrument and operating procedures are presented in this study. Different granular materials, such as steel bearing balls and sand, were tested under conditions simulating granular media flow behavior expected for the working medium in warm-forming of metal alloys sheet materials. The experiments were conducted under both static and oscillating normal loads. The static load experiments were conducted for various normal loads and shear rates, and oscillating normal load experiments were conducted under various oscillation frequencies, average normal loads and load amplitudes. During dense-packed spherical granular media flow experiments, shear stress oscillations were observed. These are attributed to the force-chain jamming behavior occurring within the granular media structure. It was also observed that granular media flow properties can be controlled by an oscillating normal load applied to the granular media. From the experimental and simulation studies it may be concluded that normal load oscillations should enhance granular media flow, which could be a great advantage for using granular media as working fluid for sheet metal forming. / text

<p align="justify">Ce travail consiste à étudier des systèmes constitués par un grand nombre de grains, auxquels de l’énergie cinétique est fournie, et à étudier leurs similarités et leurs différences avec des fluides traditionnels. Je me concentre principalement sur la nature de non-équilibre de ces fluides granulaires, en montrant que, même si les méthodes de méchanique statistique y sont applicables, leurs propriétés sont très différentes de celles de systèmes à l’équilibre ou proches de l’équilibre :</p> <ul><li>Les fluides granulaires présentent des phénomènes de transport qui n’ont pas d’équivalent dans des fluides moléculaires, tels qu’un couplage spécifique entre flux de chaleur et gradient de densité. <li>Leur distribution de vitesse est en général différente de la distribution de Maxwell-Boltzmann, et présente une surpopulation pour les grandes vitesses. <li>Dans le cas de mélanges, différentes espèces de grains sont en général caractérisées par des énergies cinétiques différentes, i.e. ces systèmes sont sujet à une non-equipartition de leur énergie. <li>Ces fluides ont tendance à former des inhomogénéités spatiales spontanément. Cette propriété est illustrée en étudiant l’expérience du Demon de Maxwell appliquée aux systèmes granulaires.</ul> <p align="justify">Chacune de ces particularités est discutée en détail dans des chapitres distincts, où l’on applique différentes méthodes de méchanique statistique (équation de Boltzmann, transition de phase, mean field models…) et où l’on vérifie les prédictions théoriques par simulations numériques (MD, Monte Carlo…).</p>

Geophysical granular flows, such as snow avalanches, pyroclastic density currents, mudslides and debris flows, can be extremely hazardous to local populations, and understanding their complex behaviour remains an important challenge. This project aims to provide insight into these events by exploring different aspects in isolation, using a combination of mathematical theory, numerical simulations and small-scale experiments. Firstly, the effect of lateral confinement is examined by studying granular material moving in an inclined chute. This can have applications to natural releases flowing down confined valleys or conduits, and the relative simplicity of the geometry also provides a useful test case for new theoretical models. One such model is the recent depth-averaged μ(I)-rheology, which, because of the viscous terms introduced into the depth-averaged momentum balance, may be described as an intermediate approach between full constitutive laws and classical shallow-water-type equations for dense granular flows. Here, a generalisation of the new system to two spatial dimensions is described, and the resulting viscous equations are able to capture the cross-slope curvature of the downslope velocity profiles in steady uniform chute flows. This may be regarded as major progress compared to traditional hyperbolic models, which only admit constant velocity solutions. Particle size-segregation in geophysical granular flows is then investigated, which can cause important feedback on the overall bulk properties as it can lead to the development of regions with different frictional properties. A particularly striking example is segregation-induced 'finger' formation, where large particles are segregated to the flow surface and sheared to form a resistive coarse-rich front, which is unstable and spontaneously breaks down into a series of lobate structures. These travel both faster and further than one might anticipate. To model such segregation-mobility feedback effects, the depth-averaged μ(I)-rheology is extended to bidisperse flows by coupling with a depth-integrated model for size-segregation. The system of equations remains mathematically well-posed and is able to qualitatively capture finger formation, with the newly-introduced viscous terms controlling the characteristics of the leveed channels that develop. A more subtle segregation effect is studied in bidisperse roll waves, which form as small irregularities merge and coarsen as they move downslope, eventually growing into destructive large amplitude pulses. Experimental measurements show lateral, as well as vertical, segregation profiles, with the coarser grains accumulating at the fastest moving wave crests. The disturbances that form in mixtures with higher proportions of large particles grow more slowly, leading to smaller amplitude waves that travel at slower speeds, and the new coupled model predicts qualitatively similar behaviour. Finally, the influence of complex topography is investigated. A smooth two-dimensional bump is placed across the width of a chute, which, depending on the initial conditions, can lead to the formation of an airborne jet or granular shock at steady state. A simple depth-averaged model in a curvilinear coordinate system following the topography accurately captures both regimes, and represents a significant improvement on using an aligned Cartesian approach.

The HydroBone is a variable stiffness load-bearing element, which utilizes jamming of granular media to achieve stiffness modulation, controlled by the application of positive pressure. Several compressive tests were conducted on the HydroBone in order to quantify the load-bearing capability of the system. It was determined that the stiffness of the HydroBone was a function of the internal pressure of the system. A controller was modeled based on this function to achieve automatic stiffness modulation of the HydroBone. An exoskeleton was designed based on the HydroBone and various actuators for the exoskeleton were considered. The HydroMuscle, a soft linear actuator was selected to provide knee actuation for the exoskeleton, based on several efficiency and force output test conducted. A knee brace was designed, capable of producing 15Nm of torque on the knee, actuated using Bowden cables coupled to the HydroMuscles.

Le broyage est une opération couramment réalisée dans de nombreux secteurs industriels. Malgré son apparente simplicité, le broyage met en jeu des phénomènes de fragmentation complexes dépendant à la fois des propriétés de la matière, des sollicitations mécaniques dans le broyeur, et de la dynamique des poudres au sein de celui-ci. Aujourd'hui l'évolution des technologies de broyage repose essentiellement sur un savoir-faire empirique et de nombreux efforts sont encore à déployer pour améliorer leur efficacité énergétique. Cette optimisation ne pourra être réalisé qu'en s'appuyant sur une connaissance fine des phénomènes mis en jeux à plusieurs échelles (échelle sub-particulaire, échelle de la particule, du lit de poudre et du procédé). L'objectif de ces travaux de thèse est de mettre en évidence les paramètres clés influençant les mécanismes de comminution et l'efficacité énergétique du broyage. Un modèle numérique de rupture de particules présentant des défauts sous forme de clivage a été mis en œuvre. Il a permis notamment d'analyser l'influence de la distribution spatiale des fissures sur la statistique des seuils de rupture en lien avec les chemins de fissures et la taille des fragments. A l'échelle du procédé, une étude expérimentale, réalisée au sein d'un broyeur de laboratoire, a permis de proposer un modèle énergétique s'inspirant de celui de Rittinger mais tenant compte des phénomènes d'agglomération. Ce modèle a ensuite été généralisé à différentes technologies de broyage à media broyant pour comparer leur efficacité énergétique lors du broyage de matières minérales, végétale ainsi qu'en condition de cobroyage. / Although grinding is a widespread operation in industrial processes, it remains poorly understood. The difficulty to model grinding not only lies in the complexity of the fragmentation, which depends on material properties and loading dynamics, but also on the stress transmission from the grinder to the particles. The development of grinding technologies has led to an empirical know-how, and much more effort is still needed to understand the the mechanisms of the comminution of particles. This objective can be achieved only by increasing knowledge on the phenomena involved at different scales (sub-particle heterogeneities, particle, powder bed and boundary conditions of the process).In this PhD work, we investigate the key parameters influencing comminution mechanisms and the energetic efficiency of grinding. A numerical model of particle breakage including a subparticle distribution of cleavages was developed. This model allowed us to analyze the cracks patterns, fragment sizes and probability distribution of failure. At the scale of the process, an extensive experimental study of comminution was carried out using a laboratory mill. An energy evolution inspired by Rittinger model but taking into account the agglomeration phenomena was proposed. This model was then extended to other grinding technologies to compare the energy efficiency for grinding minerals, vegetal particles and their comilling.

The majority of faults display a layer of crushed wear material ("fault gouge") between the fault blocks, which influences the strength and stability of faults. This thesis describes the results of a numerical model used to investigate the process of comminution in a sheared granular material. The model, based on the Discrete Element Method, simulates a layer of 2-D circular grains subjected to normal stress and sheared at constant velocity. An existing code was modified to allow grains to break when subjected to stress conditions that generate sufficient internal tensile stresses. A suite of five numerical runs was performed using the same initial system of grains with sizes randomly chosen from a pre-defined Gaussian distribution. A range of confining pressures was explored from 4.5 MPa to 27.0 MPa (in case of quartz grains with average diameter of 1 mm). The average effective friction coefficients of the five simulations were relatively unaffected by comminution and displayed a constant value of about 0.26. The amount of breakage was directly related to both the applied confining pressure and logarithm of the displacement along the fault. The particle size distribution evolved during the runs, but it was apparently determined only by the cumulative number of grain breakage events: two runs with the same number of breakage events had identical particle size distributions, even if they deformed to different extents under different stress conditions. These results suggest that the knowledge of both the local displacement and stress state on a fault can be used to infer the local particle size distribution of the gouge.