Granular materials, such as sand, are systems consisting of huge numbers of particles that interact with each other through inter-particle contacts. Different from continuum materials, a granular material displays distinctive features due to the discrete nature of the microstructure, characterized by a spatial arrangement of inter-particle connection as well as a force-chain network. With a consideration of the contact force, the overall contact network is divided into a strong sub-network and a weak sub-network that carry contacts with normal contact forces larger and lower than the average normal contact force, respectively. Thus, the fabric anisotropy for different contact networks, are employed to characterize the microstructure of the granular material. In this research, the behavior of granular materials subjected to quasi-static shear was extensively investigated in terms of the fabric evolution including the magnitude and direction of anisotropy for different contact networks. Both statistical and micromechanical approaches were adopted to obtain the macroscopic properties, such as the fabric tensor, Cauchy stress tensor and the second-order work, in terms of the micro-scale variables. The discrete element method (DEM) was employed to simulate laboratory tests along fixed loading paths; for example, 2D tests along proportional strain paths, 2D simple shear tests and 3D tests along radial stress paths on the π-plane. Results demonstrated that the induced fabric anisotropy for the overall contact network can be related to the deviatoric stress ratio for both two-dimensional and three-dimensional conditions. The relation was found to be not unique, depending on the loading paths as well as the stress state. Nevertheless, a unique linear fabric-stress relation was presented between the stress tensor and fabric tensor for the strong sub-network. Specifically, the obliquity of this linear relation was found to be a function of the mean stress. This description held true for initially isotropic specimens subjected to proportional and non-proportional loading paths. On the other hand, for the initially anisotropic specimen, this correspondence only worked at the critical stress state. According to Nicot and Darve (2006), the macro second-order work cannot be interpreted as a summation of the local second-order work from the contact plane. The second-order work induced by the fabric evolution and the volumetric change must also be taken into account. The second-order work induced by the fabric evolution cannot be neglected in 2D analysis along proportional strain paths. Moreover, the vanishing of the second-order work is related to the fabric anisotropy in contact sub-networks that the decrease of fabric anisotropy for the weak sub-network or the degradation of weak sub-network was observed to be an indicator of deformation instability even though the strong sub-network dominants the shear resistance. The degradation of strong sub-network was a necessary but not a sufficient condition of instability. The direction of the fabric anisotropy for the strong sub-network was observed to be coaxial with the orientation of the principal stress. The principal direction of fabric anisotropy for the weak sub-network was always perpendicular to that of the strong sub-network, regardless of whether the principal stress rotated or not. For the overall contact network, however, the direction of the fabric anisotropy was not necessarily in line with the major principal stress direction, even for an initial isotropic granular assembly. Therefore, the finding by Radjaï et al.(1998) that the direction of the fabric anisotropy for the weak sub-network is perpendicular to that for the overall contact network only held true for the loadings in which the critical stress could be approached no matter if the principal stress orientation rotated or not. Under this circumstance, the fabric anisotropy for the overall contact network could be interpreted as a function of sub-networks’ anisotropy weighted by the ratio of contact number in each sub-network over the total number of contacts. At critical state, both the strong sub-network and the overall contact network developed high fabric anisotropy with the weak sub-network being mostly isotropic. When plotted on the π-plane, both the fabric anisotropy for the strong sub-network and the fabric anisotropy for the overall contact network depended on the stress paths but were independent of the mean stress level. The response surface of the former could be expressed as a Lade’s surface. The response envelope of the latter was an inverted Lade’s surface. / Dissertation / Doctor of Philosophy (PhD) / In civil engineering, granular materials are ubiquitous, such as sand, gravel, rock, and concrete. Due to the discrete nature of microstructure, this type of material usually displays exceedingly complicated behaviours under shear, for example, dilatancy, non-coaxiality, critical state, instability, and anisotropy. These mechanical responses are notoriously difficult to model and most existing models are phenomenological and lack a clear physical meaning. To provide a clear physical meaning for the constitutive model of granular material, the current study explored the evolution of the microstructure within the granular material subjected to quasi-static shear and the micromechanical origins of those macroscopic behaviours such as critical state, non-coaxiality, and instability. Both micromechanical analysis and discrete element method were applied. Results showed that the evolution of the whole microstructure depended on the loading condition. However, the evolution of the microstructure joined by the ‘strong contacts’ was independent of the loading path. At critical state, the microstructure was highly anisotropic, not unique and depended on the stress paths. The rearrangement of the microstructure helped to maintain the stability of a granular material. The instability of the granular material was triggered by the failure of the microstructure joined by the ‘weak contacts’.

Many different physical systems, such as granular materials, colloids, foams and emulsions exhibit a jamming transition where the system changes from a liquid-like flowing state to a solid jammed state as the packing fraction increases. These systems are often modeled using soft-core particles with repulsive contact forces. In this thesis we explore several different dynamical models for these kinds of systems, and see how they affect the behavior around the jamming transition. We investigate the effect of different types of dissipative forces on the rheology, and study how different methods of preparing a particle configuration affect their probability to jam when quenched. We study the rheology of sheared systems close to the jamming transition. It has been proposed that the athermal jamming transition is controlled by a critical point, point J, with certain scaling properties. We investigate this using multivariable scaling analysis based on renormalization group theory to explore the scaling properties of the transition and determine the position of point J and some of the critical exponents.

Les milieux granulaires présentent une grande diversité de comportements physiques que l'on peut relier aux différents états "conventionnels" de la matière : solide, liquide ou gaz. Les travaux décrits dans ce manuscrit se concentrent sur les écoulements granulaires denses présentant de nombreuses analogies avec les liquides moléculaires. Les expériences présentées dans ce manuscrit sont réalisées en utilisant des jets granulaires s'écoulant d'un réservoir, dans l'air et sous l'effet de la gravité. Quelques propriétés de tels jets sont étudiées, notamment l'évolution du diamètre au cours de la propagation. L'évolution de cette grandeur permet une description des jets granulaires comme des fluides incompressibles dans une certaine gamme de diamètres de sortie D et de diamètres des particules d, résumés en une grandeur réduite : le rapport d'aspect D/d. Lorsque ce dernier est inférieur à une grandeur critique proche de 15, les jets granulaires cessent de se comporter comme des liquides incompressibles et sont alors décrits comme des gaz en expansion.La transition entre les deux régimes d'écoulements est expliquée par un modèle faisant intervenir l'équilibre entre la température granulaire et sa dissipation par l'inélasticité des collisions entre les billes constituant le milieu granulaire. En utilisant les mesures de la température granulaire accessibles à la paroi dans le réservoir, ce modèle permet d'obtenir les profils de température et de fraction volumique du milieu en fonction du rapport d'aspect ainsi que leurs valeurs moyennes, présentant un bon accord avec les mesures de la fraction volumique en sortie du réservoir.Dans le régime "liquide" des jets granulaires mis en évidence ici, une tension de surface effective est mesurée par l'étude d'une instabilité similaire à celle de Rayleigh-Plateau. En soumettant le jet à une oscillation verticale apparaît une modulation du diamètre du jet dont il est possible d'étudier l'évolution au cours du temps. La mesure des taux de croissance des modes instables excités permet d'établir la relation de dispersion et d'obtenir une tension de surface effective dans les jets granulaires. Il est montré que cette tension de surface effective décroit lorsque la taille des particules augmente, décroit lorsque la pression de l'air ambiant diminue et augmente avec la distance de propagation.Le mécanisme proposé pour expliquer l'origine de cette tension de surface effective est l'interaction entre le jet granulaire et l'air ambiant. Les profils de vitesse de l'air entraîné par le jet sont mesurés pour différentes diamètres de particules, différentes pression ambiantes et différentes distances de propagation. L'entraînement de l'air et les profils de vitesses sont utilisés pour définir certaines forces s'exerçant sur les billes et construire une tension de surface effective : l'ordre de grandeur de cette tension de surface est incompatible avec les mesures réalisées précédemment. Une mesure de la pression de l'air à l'intérieur du jet granulaire permet d'obtenir une force exercée par la perméation de l'air à travers les pores du jet dont l'ordre de grandeur est correct. / Granular media exhibit a broad range of behaviours that can be related to the common states of matter: solid, liquid and gaseous. The experiments described in this thesis focus on dense granular flows ad their analogies with molecular liquid flows.The work presented focuses on granular material flowing from a reservoir, in ambient air under the effect of gravity. Some properties of such jets are presented, among them the evolution of the diameter of the jet along propagation. This evolution allows one to describe granular jets as incompressible liquid jets for a certain range of parameters D (exit diameter) and d (beads diameter). When using a reduced variable D/d (the aspect ratio), a transition appears close to a critical value (approx. 15) below which the granular jet exhibit a gas-like behaviour.This transition is explained using a model supposing balance between the heat flux (from the granular temperature imposed at the wall of the reservoir) and its dissipation through inelastic collisions between the beads in the granular medium. This model allows one to compute the temperature and volume fraction profiles as well as their mean values which are in good agreement with the experimental measurements (volume fraction at the exit).In the "liquid" regime defined previously, an effective surface tension is measured by studying the unstable modes of a Rayleigh-Plateau like instability. This instability is obtained by imposing a vertical oscillation on the jet which induces a diametrical modulation whose evolution is measured. Measurements of the growth rates of these unstable modes leads to the dispersion relation $\omega (kr_{0})$ and to an effective granular surface tension. This surface tension shows a diminution when the beads' size increases, a diminution when the air pressure is reduced and a growth along propagation.The proposed mechanism explaining this effective surface tension is the interaction between the granular jet and the surrounding air. Air velocity profiles are measured for different beads diameters, different air pressures and different distances below the outlet. Using these velocity profiles, various forces exerted on the beads are calculated, leading to a surface tension whose order of magnitude is lower than the one measured through the Rayleigh-Plateau instability. The right order of magnitude can be obtained by considering the air permeation through the pores on the surface the jet and the force exerted along the surface of said pores.

Nesta dissertação de mestrado é estudado o desempenho fluidodinâmico de um meio poroso fixo e compactado, construído por sinterização com esferas de vidro para a retenção de partículas. A análise experimental visou o processo de retenção de partículas a partir de pastilhas circulares de diâmetro de 29 mm confeccionadas com esferas de vidro variando de 1,0 a 3,3 mm de diâmetro e sinterizadas como um elemento rígido a partir de aquecimento contínuo até cerca de 750ºC. As pastilhas foram submetidas a diferentes pressões de coluna de água, e a vazão no meio poroso foi analisada para diferentes pressões. Os experimentos foram realizados com a adição em batelada de polpa de açaí, areia fina, areia grossa e esferas de vidro próprias da composição do meio poroso. As vazões mássicas adimensionais são apresentadas graficamente para diferentes pressões de coluna de água variando entre 0,1 e 0,5 atmosferas (atm), em regime permanente e estacionário. Os resultados experimentais foram comparados e apresentados na forma de parâmetros adimensionais que caracterizam o regime de escoamento num leito fixo. Os resultados experimentais foram modelados a partir da modificação dos modelos de Vortmeyer e Schuster (1983) e Subagyo et al. (1998) para estabelecer sobre os mesmos parâmetros adimensionais uma adequada aproximação com os resultados teóricos. / The present dissertation reports the performance of steady flow in circular fix bed which was created by sinterization of glass spheres. The experimental analysis aimed the process of retention of particles from circular packed bed of 29 mm of diameter. The circular fix bed was created with spheres of glass of diameter between 1.0 and 3.0 mm, and made by sintering one rigid body from continuous heating until 750ºC. The circular and rigid fix bed was subjected to different pressures of column of water varying between 0.1 and 0.5 atm for analysis of flux (kg/s). The experiments were carried out with the addition of one amount of açai pulp, sands fine, sands thick and spheres of glass own of composition of fix bed. The dimensionless flux was present for different pressures of column of water on the fix bed; the results were compared and presented in the form of dimensionless parameters of literature what characterize the flow in packed bed. The experimental results were modeled based on Vortmeyer e Schuster (1983) and Subagyo et al. (1998) models, establishing on the dimensionless parameters an appropriate approach with the theoretical flux of circular fix bed.

Les systèmes de stockage d'énergie thermique sont des éléments centraux de divers types de centrales de production d'énergie fonctionnant à l'aide de sources d'énergie renouvelables. Ces systèmes de stockage thermique de type solide/fluide peuvent être considérés comme une solution rentable dans les centrales solaires à concentration. Un tel dispositif est constitué d'un réservoir rempli d'un lit granulaire à travers lequel circule un fluide caloporteur. Cependant, dans de tels dispositifs, le réservoir pourrait être soumis à une accumulation de contraintes thermiques au cours des cycles de chargement et de déchargement en raison de la dilatation thermique différentielle entre le milieu granulaire et la paroi du réservoir. Cette thèse a été consacrée à l'étude du comportement thermomécanique du lit granulaire à l'intérieur d'un réservoir de stockage thermique de type régénérateur solide/fluide. Pour atteindre cet objectif, deux approches ont été suivies : les approches numériques et expérimentales. Un modèle numérique basé sur la méthode des éléments discrets a été développé pour décrire le comportement du réservoir sous cyclage thermique. L'évolution des contraintes appliquées aux parois de la cuve au cours des cycles thermiques, est étudiée en tenant compte à la fois des charges thermiques et mécaniques, ainsi que de la cinématique du milieu granulaire à l'échelle des particules (c'est-à-dire des éléments discrets) et de la déformation thermo-mécanqiue du réservoir. Des simulations ont été effectuées pour différentes configurations thermiques (chauffage/refroidissement homogène du réservoir sur sa hauteur ou gradient vertical de température) et différents cas de condition limite (paroi rigide, paroi du réservoir avec un coefficient de dilatation thermique supérieur au lit de roche ou inversement). Le comportement du réservoir dépend des conditions thermiques et conditions aux limites imposées. De plus, un prototype de thermocline a été conçu et construit au sein du laboratoire au CEA, visant à étudier l'accumulation de contraintes sur les cycles thermiques. Le dispositif expérimental, appelé ESPERA, est équipé de dispositifs de mesure de force installés à différentes hauteurs sur la paroi du réservoir. Les dispositifs de mesure de force ont été développés et calibrés au CEA. Leur sensibilité a également été testée en développant un autre banc expérimental, P'tit- Pousse. Des essais expérimentaux ont été réalisés permettant de prouver l'accumulation des contraintes au cours des cycles. Finalement, une comparaison entre les résultats numériques et les premiers résultats expérimentaux obtenus en fin de thèse est proposée. / Thermal Energy Storage (TES) systems are central elements of various types of power plants operated using renewable energy sources. Packed bed TES can be considered as a cost effective solution in concentrated solar power plants (CSP). Such a device is made of a tank filled with a granular bed through which a heat-transfer fluid circulates. However, in such devices, the tank might be subjected to an accumulation of thermal stresses during cycles of loading and unloading due to the differential thermal expansion between the filler and the tank wall. This research was devoted to investigate the thermo-mechanical behavior of the granular bed inside a packed bed TES tank. To achieve this objective, two approaches were undertaken in this work, i.e. numerical and experimental. A numerical model was defined to describe the tank's behavior under thermal cycling based on the discrete element method (DEM). The evolution of tank wall stresses over thermal cycles, taking into account both thermal and mechanical loads, as well as the kinematics of the granular material at the particles scale (i.e. discrete elements), are studied here. The deformability of the tank itself under thermo-mechanical loads is also included in the numerical model. Simulations were performed for different thermal configurations (i.e. the tank is heated homogeneously along its height or with a moving vertical gradient of temperature) and different boundary condition cases (i.e. rigid wall, tank wall with a higher thermal expansion coeficient than the bed or inversely). The behavior of the tank is dependent on the imposed thermal and boundary conditions. In addition to this, a thermocline prototype was designed and constructed at the CEA laboratory, aiming at studying the stress accumulation over the thermal cycles. The experimental setup, called ESPERA, is equipped with force measurement devices, installed at different height positions on the wall. The force measurement devices were developed and calibrated at the CEA. Their sensitivity was also tested using a different developed setup, P'tit-Pousse. Experimental tests were carried out proving the stress accumulation over the cycles. Eventually, a comparison between the numerical results and the lately-obtained preliminary experimental measurements is proposed.

L'objectif des travaux présentés dans ce mémoire est de caractériser la texture et la rhéologie des milieux granulaires en fonction de la polydispersité de forme et de taille des particules mais aussi en fonction de la cohésion interne des particules lorsqu'elles sont fragmentables, en vue d'une meilleure compréhension du procédé de fabrication des compacts. Pour ces études, nous avons utilisé la méthode de Dynamique des Contacts avec un modèle de rupture des particules. Nos analyses montrent que la polydispersité de forme peut jouer un rôle important lorsque la polydispersité de taille est faible. Par exemple, la résistance au cisaillement est presque indépendante de la polydispersité de taille mais elle diminue lorsque les formes deviennent plus irrégulières. La fragmentation des particules est fortement hétérogène en raison de la redistribution des contraintes au sein du matériau. Celui-ci garde la mémoire de la distribution granulométrique initiale, mais une classe intermédiaire de tailles se développe avec une distribution en loi de puissance des tailles et un rapport d'aspect moyen proche du nombre d'argent. Au cours du cisaillement, les déformations se localisent dans des bandes avec une compacité supérieure au reste du matériau en raison de la fragmentation des particules. La fragmentation tend également à annuler la dilatance et le pic de contrainte. / The general objective of the work presented in this dissertation is to investigate the microstructure and rheology of granular materials as a function of size and shape polydispersity of the particles, and to analyze the role of particle fragmentation as a function of the internal cohesion of particles in view of a better understanding of the manufacture process of powder compacts. For this work, we used numerical simulations by means of the Contact Dynamics method with a model of particle fracture. Our results suggest that shape polydispersity may play an important role when size polydispersity is low. For example, the shear strength is nearly independent of size distribution but declines when the particles becomes increasingly more irregular in shape. The process of particle fragmentation is found to be highly inhomogenious as a result of stress redistribution. The memory of the initial size distribution is mainly conserved in the class of larger particles while a class of intermediate sizes develops with a power-law size distribution and a mean aspect ratio close to the silver number independently of the initial size distribution. During shear, the strain is localized in shear bands of large solid fraction as a consequence of particle fragmentation and enhanced size polydispersity. Particle fragmentation tends to reduce dilatancy and the peak shear strength.

Μελετάμε την ροή κοκκώδους σε κεκλιμένη πειραματική διάταξη δυο διαστάσεων, αποτελούμενη από Κ το πλήθος γραμμές και Μ το πλήθος στήλες δοχείων, τα οποία αναταράσσονται κάθετα. Η ροή του υλικού από δοχείο σε δοχείο περιγράφεται από ένα μοντέλο ροής [Eggers, 1999; Van der Weele, 2008]. Υποκινούμενοι από δυσλειτουργίες που παρουσιάζονται στις σύγχρονες βιομηχανικές μονάδες μεταφοράς (όπως είναι ο σχηματισμός συσσωματωμάτων), εισάγουμε σταθερή ποσότητα υλικού στην πρώτη γραμμή των δοχείων, και καθορίζουμε τις συνθήκες κάτω από τις οποίες η ροή παραμένει ομαλή και συνεχής μέχρι την τελευταία γραμμή. Ενώ στην περίπτωση μιας και μόνο σειράς δοχείων (Μ=1) η εκροή μηδενίζεται με την εμφάνιση ενός και μόνο συσσωματώματος [Κανελλόπουλος, 2008], για Μ>1 απαιτούνται περισσότερα συσσωματώματα για τον μηδενισμό της. Μελετάμε τον τρόπο με τον οποίο αυτά τα συσσωματώματα διατάσσονται στα δοχεία, ο οποίος πολλές φορές όπως βλέπουμε μπορεί να είναι ιδιαίτερα πολύπλοκος, αποτελώντας έτσι ένα εξαίρετο παράδειγμα μορφογένεσης σε δυναμικά συστήματα [Cross and Hohenberg, 1993]. Εντοπίζουμε τα βασικά χαρακτηριστικά αυτής της μορφογένεσης και εξηγούμε πως αυτά σχετίζονται με το μοντέλο ροής. Για την περαιτέρω μαθηματική και φυσική τους ερμηνεία προτείνουμε το συνεχές όριο του μοντέλου ροής, το οποίο θα αποτελέσει την απαρχή για μελλοντικές έρευνες [Van der Weele et al, 2008]. Αναφορές: •J. Eggers, Sand as Maxwell’s demon, Phys. Rev. Lett. 83, 5322 (1999). •K. van der Weele, Granular gas dynamics: How Maxwell’s demon rules in a nonequilibrium system, Contemporary Phys. 49, 157-175 (2008). •Γ. Κανελλόπουλος, Οριακή ροή κοκκώδους υλικού σε διάδρομο μεταφοράς, Διπλωματική Εργασία, Τμήμα Μαθηματικών, Πανεπιστήμιο Πατρών (2008). •M.C. Cross and P.C. Hohenberg, Pattern formation outside of equilibrium, Rev.Mod.Phys. 65, 851 (1993). •K. van der Weele, G. Kanellopoulos, C. Tsiavos, and D. van der Meer, Transient granular shock waves and upstream motion on a staircase (submitted, 2009). / We study the dynamics of granular material in a 2-dimensional tilted setup, consisting of K rows and M columns of equal sized compartments, which is brought into motion by vertical shaking. Particles are inserted into the system along the upper row of compartments, then flow downwards, and eventually exit the system from the bottom row. Similar setups are encountered frequently in industrial transport machinery and are notorious for the tendency of the particles to form dense clusters, which obstruct the flow. We model the particle flow from box to box by a flux function and determine the maximal value of the inflow rate for which the flow remains steady. If the inflow rate exceeds this value, clusters are formed. The way in which these clusters are distributed over the KxM compartments is a fine example of spontaneous pattern formation. We analyze the main characteristics of this cluster formation, its dependence on the various parameters of the system, and its sensitivity to experimental fluctuations.

Previous research has shown that the sample preparation method used to reconstitute specimens for granular materials can have a significant impact on its mechanistic behavior. As the Discrete Element Method becomes a more popular choice for modeling multiphysics problems involving granular materials, the sample heterogeneity should be correctly characterized in order to obtain accurate results. In order to capture the effect of sample preparation on the homogeneity of the sample, standard procedures were used to reconstitute samples composed of a homogeneous granular material. X-ray computed tomography and image analysis techniques were then used to characterize the spatial heterogeneity of a typical sample. The sample preparation method was modeled numerically using the Discrete Element program PFC3D. The resulting microstructure of the numerical sample was compared to the results of the image analysis to determine if the heterogeneity of the sample could be reproduced correctly for use in Discrete Element Modeling.

La culture du blé est l’une des plus importantes au monde. Le grain de blé est un matériau composite naturel dont la majeure partie est constituée d’albumen amylacé formé d’un assemblage compact de granules d’amidons (glucides) enchâssés dans une matrice protéique (gluten). Pour obtenir des produits comme la farine, la structure de l'albumen doit être fragmentée en broyant les grains sous des fortes contraintes. La quantité et la qualité des produits obtenus dépendent du comportement de l’albumen à la fragmentation. En raison de sa nature composite, le comportement rhéologique du grain est tributaires des propriétés mécaniques des phases qui le composent (granules, gluten, pores), de leurs interactions, ainsi que de leur distribution spatiale. Les granules d’amidons sont de formes relativement sphériques et de tailles micrométriques, tandis que les protéines sont organisées en un réseau entourant les granules. L'interaction entre l'amidon et ce réseau protéique est influencée par certaines protéines, les puroindolines, dont la présence et le type d’allèle sont contrôlées génétiquement. Si les gènes codant pour les puroindolines sont présents sous forme sauvages, la dureté meunière, c’est à dire l’aptitude à la fragmentation du grain est faible. L’origine de ce comportement est liée à une adhérence limitée entre matrice protéique et amidon. L'absence totale de puroindolines chez le blé dur conduit au contraire à une dureté très élevée des grains et à une forte adhérence. L'objectif de cette thèse est d'étudier, à partir d’une approche multidisciplinaire, la biomécanique du fractionnement du grain de blé en mettant l'accent sur le rôle des granules d'amidon. Des échelles de taille différentes sont considérées : échelle micrométrique du granule et de la matrice protéique; agencement complexe de ces composants dans l'albumen et échelle millimétrique du grain. Ainsi, des expériences de broyage à l'échelle du grain ont été combinées avec des mesures nano-mécaniques par microscopie à force atomique (AFM) et des simulations numériques.Le comportement au broyage a été étudié en utilisant un micro-moulin instrumenté. Une comparaison a été effectuée entre des essais réalisés sur une variété de blé dur et sur la même variété dans laquelle ont été introduits les gènes codant pour les puroindolines. Un changement significatif du comportement mécanique des grains transformés, attribuable uniquement à la présence de puroindolines, a été observé - en termes d'énergie consommée, - de productivité en farine et - de taux d'amidon endommagé. Ces changements sont compatibles avec l'hypothèse d'une faible adhérence, entre granules d'amidon et matrice protéique, induite par la présence des puroindolines et montrent l'effet significatif de celles-ci sur le comportement à la fragmentation. Ces modifications de comportement mécanique peuvent être étudiées par des mesures AFM nano-mécaniques. Pour compléter des travaux antérieurs ayant permis la mesure des propriétés de l'amidon et du gluten, une méthode basée sur des mesures AFM en mode résonance de contact (CR-AFM) a été développée. Celle-ci permet de cartographier les propriétés directement à l'intérieur des granules d’amidon et prend en compte à travers un modèle théorique les variations importantes de topographie observées dans les sections de grains. Ces études CR-AFM de l'albumen ont ensuite porté sur les propriétés mécaniques des granules d'amidon d'origines botaniques différentes (céréales et légumineuses).Enfin, le rôle de la distribution bimodale en taille des granules d'amidon sur la fragmentation de l'albumen a été précisé à partir d’une étude numérique paramétrique détaillée. Les propriétés mécaniques élastiques et à la rupture ont été analysées en détail, ainsi que le rôle dominant de la ténacité des granules et de l'adhérence à l'interface sur l’endommagement de l’amidon. / The wheat grain is a natural composite material of worldwide importance. The major part of the grain is the starchy endosperm. To obtain food products, such as flour, the endosperm’s compact structure needs to be disintegrated, which is achieved by milling the grains under high forces. The quantity and quality of the milling products notably depend on the fragmentation behaviour of the endosperm.Due to the endosperm’s composite nature, this behaviour depends strongly on the mechanical properties of its components and their interaction. The main components of the endosperm are carbohydrates and proteins. The carbohydrates are deposited as starch in the form of granules of micro-meter size, whereas proteins form a network (gluten), which surrounds the starch granules. The interactions between starch and proteins is believed to be influenced by certain non-gluten proteins (puroindolines), whose presence and allelic state are genetically controlled. If puroindoline genes are present in the wild-type form, grain hardness is low, which have been related to low starch-protein adhesion. The complete absence of puroindolines in the durum wheat species leads to very high grain hardness and indicates a strong adhesion.The aim of this thesis was to investigate the biomechanics of wheat grain fractionation with a focus on the role of the starch granules therein, which was pursued with a multi-disciplinary approach. Different size scales were considered, from the micro meter-sized structures of starch and protein, the complexity of their arrangement in the endosperm, up to the millimeter-sized grains. In this work, grain-scale milling experiments were combined with nano-mechanical measurements by atomic force microscopy (AFM) and numerical simulations.The milling behaviour of a transgenic durum wheat line, which contained puroindoline genes, was determined by grain scale milling experiments and compared to the milling behavior of non-modified durum wheat. A significant change of milling behavior of the transformed durum wheat grains was observed in terms of milling energy, flour yield and starch damage, which was solely attributable to the presence of puroindolines. The observed changes were consistent with the hypothesis of a lower adhesion between starch granules and protein matrix due to the presence of puroindolines and confirmed the significant effect of puroindolines on the fragmentation behaviour, independent of the grain’s genetic background.The change of fragmentation behaviour is a result of modifications of the mechanical properties of the endosperm’s components and/ or their interaction. Such modifications can be investigated by AFM nano-mechanical measurements. Based on previous work illuminating the global nano-mechanical properties of starch and gluten, contact-resonance AFM (CR-AFM) was applied to obtain maps of the nano-mechanical properties inside the grains. Due to the high topography variations of grain section surfaces and the non-trivial correlation between surface slope and contact resonance-frequency, which hindered a straight-forward interpretation of CR-AFM measurements, a practical method based on existing analytical models of the cantilever vibration was developed to correct the measurements. CR-AFM studies of the endosperm were then focused specifically on the mechanical properties of starch granules and the link to starch structure, and applied to the study of starches from wheat in comparison to plants from different botanical origin (other cereals and legumes).Finally, the role of starch granules, their size distribution, and mechanical properties on endosperm fragmentation was analysed by parametric numerical studies. The influence of the bi-modal size distribution of granules on the mesoscale mechanical properties was shown, as well as the governing role of granule toughness and interface adhesion on the granule damage.

Nesta dissertação de mestrado é estudado o desempenho fluidodinâmico de um meio poroso fixo e compactado, construído por sinterização com esferas de vidro para a retenção de partículas. A análise experimental visou o processo de retenção de partículas a partir de pastilhas circulares de diâmetro de 29 mm confeccionadas com esferas de vidro variando de 1,0 a 3,3 mm de diâmetro e sinterizadas como um elemento rígido a partir de aquecimento contínuo até cerca de 750ºC. As pastilhas foram submetidas a diferentes pressões de coluna de água, e a vazão no meio poroso foi analisada para diferentes pressões. Os experimentos foram realizados com a adição em batelada de polpa de açaí, areia fina, areia grossa e esferas de vidro próprias da composição do meio poroso. As vazões mássicas adimensionais são apresentadas graficamente para diferentes pressões de coluna de água variando entre 0,1 e 0,5 atmosferas (atm), em regime permanente e estacionário. Os resultados experimentais foram comparados e apresentados na forma de parâmetros adimensionais que caracterizam o regime de escoamento num leito fixo. Os resultados experimentais foram modelados a partir da modificação dos modelos de Vortmeyer e Schuster (1983) e Subagyo et al. (1998) para estabelecer sobre os mesmos parâmetros adimensionais uma adequada aproximação com os resultados teóricos. / The present dissertation reports the performance of steady flow in circular fix bed which was created by sinterization of glass spheres. The experimental analysis aimed the process of retention of particles from circular packed bed of 29 mm of diameter. The circular fix bed was created with spheres of glass of diameter between 1.0 and 3.0 mm, and made by sintering one rigid body from continuous heating until 750ºC. The circular and rigid fix bed was subjected to different pressures of column of water varying between 0.1 and 0.5 atm for analysis of flux (kg/s). The experiments were carried out with the addition of one amount of açai pulp, sands fine, sands thick and spheres of glass own of composition of fix bed. The dimensionless flux was present for different pressures of column of water on the fix bed; the results were compared and presented in the form of dimensionless parameters of literature what characterize the flow in packed bed. The experimental results were modeled based on Vortmeyer e Schuster (1983) and Subagyo et al. (1998) models, establishing on the dimensionless parameters an appropriate approach with the theoretical flux of circular fix bed.