Pagonabarraga, I. (Ignacio)
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- Influence of the feeding mechanism on deposits of square particles(2013) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Cruz-Hidalgo, R. (Raúl); Acevedo-Escalante, M. (Manuel Francisco); Maza-Ozcoidi, D. (Diego)In a previous paper [Hidalgo et al., Phys. Rev. Lett. 103, 118001 (2009)] it was shown that square particles deposited in a silo tend to align with a diagonal parallel to the gravity, giving rise to a deposit with very particular properties. Here we explore, both experimentally and numerically, the effect on these properties of the filling mechanism. In particular, we modify the volume fraction of the initial configuration from which the grains are deposited. Starting from a very dilute case, increasing the volume fraction results in an enhancement of the disorder in the final deposit characterized by a decrease of the final packing fraction and a reduction of the number of particles oriented with their diagonal in the direction of gravity. However, for very high initial volume fractions, the final packing fraction increases again. This result implies that two deposits with the same final packing fraction can be obtained from very different initial conditions. The structural properties of such deposits are analyzed, revealing that, although the final volume fraction is the same, their micromechanical properties notably differ.
- Stress transmission in systems of faceted particles in a silo: the roles of filling rate and particle aspect ratio(Springer, 2014) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Cruz-Hidalgo, R. (Raúl); Alonso-Marroquin, F. (F.); Acevedo-Escalante, M. (Manuel Francisco); Maza-Ozcoidi, D. (Diego)We present experimental and numerical results for particle alignment and stress distribution in packings of faceted particles deposited in a small-scale bi-dimensional silo. First, we experimentally characterize the deposits’ morphology in terms of the particles’ aspect ratio and feeding rate. Then we use the experimental results to validate our discrete element method (DEM) based on spheropolygons. After achieving excellent agreement, we use contact forces and fabric provided by the simulations to calculate the coarse-grained stress tensor. For low feeding rates, square particles display a strong tendency to align downwards, i.e., with a diagonal parallel to gravity. This morphology leads to stress transmission towards the walls, implying a quick development of pressure saturation, in agreement with the Janssen effect. When the feed rate is increased, both the disorder and the number of horizontal squares in the silo increase, hindering the Janssen effect. Conversely, for elongated particles the feed rate has a weak effect on the final deposit properties. Indeed, we always observe highly ordered structures of horizontal rods where the stress is transmitted mainly in the vertical direction.
- Flow of colloidal suspensions through small orifices(2018) Pagonabarraga, I. (Ignacio); Hernandez-Puerta, A. (A.); Cruz-Hidalgo, R. (Raúl); Goñi-Arana, A. (Ane)In this work, we numerically study a dense colloidal suspension flowing through a small outlet driven by a pressure drop using lattice-Boltzmann methods. This system shows intermittent flow regimes that precede clogging events. Several pieces of evidence suggest that the temperature controls the dynamic state of the system when the driving force and the aperture size are fixed. When the temperature is low, the suspension's flow can be interrupted during long time periods, which can be even two orders of magnitude larger than the system's characteristic time (Stokes). We also find that strong thermal noise does not allowthe formation of stable aggregate structures avoiding extreme clogging events, but, at the same time, it randomizes the particle trajectories and disturbs the advective particle flow through the aperture. Moreover, examining the particle velocity statistics, we obtain that in the plane normal to the pressure drop the colloids always move as free particles regardless of the temperature value. In the pressure drop direction, at high temperature the colloids experience a simple balance between advective and diffusive transport, but at low temperature the nature of the flow is much more complex, correlating with the occurrence of very long clogging events.
- Clogging transition of many-particle systems flowing through bottlenecks(2014) Clement, E. (E.); Pugnaloni, L.A. (Luis A.); Parisi, D.R. (D. R.); Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Peralta, J.P. (Juan Pablo); Cruz-Hidalgo, R. (Raúl); Ferrer, L.M. (Luis Miguel); Lozano, C. (Celia); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel); Gago, P.A. (Paula A.)
- Granular packings of elongated faceted particles deposited under gravity(2010-06-28) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Cruz-Hidalgo, R. (Raúl); Maza-Ozcoidi, D. (Diego)We report experimental and theoretical results of the effect that particle shape has on the packing properties of granular materials. We have systematically measured the particle angular distribution, the cluster size distribution and the stress profiles of ensembles of faceted elongated particles deposited in a bidimensional box. Stress transmission through this granular system has been numerically simulated using a two-dimensional model of irregular particles. For grains of maximum symmetry (squares), the stress propagation localizes and forms chain-like forces analogous to those observed for granular materials composed of spheres. For thick layers of grains, a pressure saturation is observed for deposit depths beyond a characteristic length. This scenario correlates with packing morphology and can be understood in terms of stochastic models of aggregation and random multiplicative processes. As grains elongate and lose their symmetry, stress propagation is strongly affected. Lateral force transmission becomes less favored than vertical transfer, and hence, an increase in the pressure develops with depth, hindering force saturation.
- Rheological behavior of colloidal suspension with long-range interactions(2018) Pagonabarraga, I. (Ignacio); Cruz-Hidalgo, R. (Raúl); Malgaretti, P. (P.); Arietaleaniz-Coranti, S. (Sara)In this work, we study the constitutive behavior of interacting colloidal suspensions for moderate and high concentrations. Specifically, using a lattice Boltzmann solver, we numerically examine suspensions flowing through narrow channels, and explore the significance of the interaction potential strength on the system's macroscopic response. When only a short-range interaction potential is considered, a Newtonian behavior is always recovered and the system's effective viscosity mostly depends on the suspension concentration. However, when using a Lennard-Jones potential we identify two rheological responses depending on the interaction strength, the volume fraction, and the pressure drop. Exploiting a model proposed in the literature we rationalize the simulation data and propose scaling relations to identify the relevant energy scales involved in these transport processes. Moreover, we find that the spatial distribution of colloids in layers parallel to the flow direction does not correlate with changes in the system macroscopic response; but, interestingly, the rheology changes do correlate with the spatial distribution of colloids within individual layers. Namely, suspensions characterized by a Newtonian response display a cubiclike structure of the colloids within individual layers, whereas for suspensions with non-Newtonian response colloids organize in a hexagonal structure.
- Role of Particle Shape on the Stress Propagation in Granular Packings(American Physical Society, 2009-09-11) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Cruz-Hidalgo, R. (Raúl); Maza-Ozcoidi, D. (Diego)We present an experimental and numerical study on the influence that particle aspect ratio has on the mechanical and structural properties of granular packings. For grains with maximal symmetry (squares), the stress propagation in the packing localizes forming chainlike forces analogous to the ones observed for spherical grains. This scenario can be understood in terms of stochastic models of aggregation and random multiplicative processes. As the grains elongate, the stress propagation is strongly affected. The interparticle normal force distribution tends toward a Gaussian, and, correspondingly, the force chains spread leading to a more uniform stress distribution reminiscent of the hydrostatic profiles known for standard liquids.
- Influence of the feeding rate on the packing properties of faceted particles(AIP Publishing, 2013) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Cruz-Hidalgo, R. (Raúl); Acevedo-Escalante, M. (Manuel Francisco); Maza-Ozcoidi, D. (Diego)The effect of the filling mechanism on the packing of faceted particles with different aspect ratios has been examined. We have experimentally measured the particle angular distribution and the packing fraction of ensembles of faceted particles deposited in a bidimensional box. The granular system has been numerically simulated using a two-dimensional model of faceted particles. We found that increasing the feeding rate results in an enhancement of the disorder in the final deposit and, consequently, in a reduction of the number of particles oriented in their most stable configuration. In this regime, the final packing fraction monotonically decreases as the feeding rate increases. The correlations between the final packing morphology and the stress transmission were examined by describing the micromechanical properties of the deposits. For the case of elongated particles, increasing the feeding rate leads to an enhancement of the stress transmission towards the sides of the box. On the contrary, for the case of square particles, increasing the feeding rate promotes vertical transmission of the stress.
- Stress distribution of faceted particles in a silo after its partial discharge(EDP Sciences / Springer-Verlag, 2011-12-28) Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Hidalgo, R.C. (R. C.); Kanzaki, T. (T.); Acevedo-Escalante, M. (Manuel Francisco); Maza-Ozcoidi, D. (Diego)We present experimental and numerical results of the effect that a partial discharge has on the morphological and micro-mechanical properties of non-spherical, convex particles in a silo. The comparison of the particle orientation after filling the silo and its subsequent partial discharge reveals important shearinduced orientation, which affects stress propagation. For elongated particles, the flow induces an increase in the packing disorder which leads to a reduction of the vertical stress propagation developed during the deposit generated prior to the partial discharge. For square particles, the flow favors particle alignment with the lateral walls promoting a behavior opposite to the one of the elongated particles: vertical force transmission, parallel to gravity, is induced. Hence, for elongated particles the flow developed during the partial discharge of the silo leads to force saturation with depth whereas for squares the flow induces hindering of the force saturation observed during the silo filling.
- Brittle-to-ductile transition in a fiber bundle with strong heterogeneity(American Physical Society, 2013-04-29) Pagonabarraga, I. (Ignacio); Kun, F. (Ferenc); Kovács, K. (Kornél); Cruz-Hidalgo, R. (Raúl)We analyze the failure process of a two-component system with widely different fracture strength in the framework of a fiber bundle model with localized load sharing. A fraction 0 α 1 of the bundle is strong and it is represented by unbreakable fibers, while fibers of the weak component have randomly distributed failure strength. Computer simulations revealed that there exists a critical composition αc which separates two qualitatively different behaviors: Below the critical point, the failure of the bundle is brittle, characterized by an abrupt damage growth within the breakable part of the system. Above αc, however, the macroscopic response becomes ductile, providing stability during the entire breaking process. The transition occurs at an astonishingly low fraction of strong fibers which can have importance for applications. We show that in the ductile phase, the size distribution of breaking bursts has a power law functional form with an exponent μ = 2 followed by an exponential cutoff. In the brittle phase, the power law also prevails but with a higher exponent μ = 9 2. Thetransition between the two phases shows analogies to continuous phase transitions. Analyzing the microstructure of the damage, it was found that at the beginning of the fracture process cracks nucleate randomly, while later on growth and coalescence of cracks dominate, which give rise to power law distributed crack sizes.