Flows of granular material in two-dimensional channels

Secondary cone-type crushing machines are an important part of the aggregate production process. These devices process roughly crushed material into aggregate of greater consistency and homogeneity. We apply a continuum model for granular materials (`A Constitutive Law For Dense Granular Flows', Nature 441, p727-730, 2006) to flows of granular material in representative two-dimensional channels, applying a cyclic applied crushing stress in lieu of a moving boundary. Using finite element methods we solve a sequence of quasi-steady fluid problems within the framework of a pressure dependent particle size problem in time. Upon approximating output quantity and particle size we adjust the frequency and strength of the crushing stroke to assess their impact on the output

Investigating instability in granular materials by means of a microstructural model

International audienceUnder certain loading conditions, instability in loose sand can develop at a shear stress level much lower than the critical state failure line. To analyse these types of problems, we adopt the micromechanical approach developed earlier for the modelling of granular material behaviour. The stress-strain relationship for a granular assembly is determined by integrating the behaviour of the inter-particle contacts in all orientations. The constitutive model is applied to simulate undrained triaxial and constant-q tests on loose sand. Numerical simulations are compared to experimental results in order to evaluate the model's ability to predict the different modes of instability of the granular assembly. With the model we have also analysed instability at inter-particle level to observe how it is connected to instability at the assembly level.Dans certaines conditions de chargement, des ruptures par instabilité peuvent prendre naissance dans les sables lâches pour des niveaux de contraintes très nettement inférieurs à ceux correspondant à la plasticité parfaite. Pour analyser ce type de problèmes, nous adoptons une approche d'homogénéisation développée précédemment pour la modélisation du comportement des matériaux granulaires. La relation contrainte-déformation macroscopique est obtenue en intégrant le comportement défini au niveau du contact inter-granulaire. Le modèle est utilisé pour simuler des essais non drainés et des essais à déviateur constant sur un sable lâche. Les résultats de la simulation à l'échelle macroscopique sont comparés à des résultats expérimentaux de façon à apprécier la capacité du modèle à prédire la naissance de l'instabilité sur ces chemins particuliers. Une analyse à l'échelle des différents plans de contact inter-granulaire a également été entreprise afin de relier les conditions d'instabilité aux différentes échelles

Numerical modeling of pile penetration in silica sands considering the effect of grain breakage

202308 bcchAccepted ManuscriptOthersNational Natural Science Foundation of ChinaPublishe

Bifurcations in granular media: macro- and micro-mechanics approaches

International audienceVarious failure modes related to different kinds of bifurcations occur in nonassociated elastoplastic materials such as geomaterials. After presenting experimental evidence, we study this question by means of phenomenological constitutive relations and direct numerical simulations based on the discrete element method. The second-order work criterion related to diffuse failure modes is particularly considered within the framework of continuum and discrete mechanics. The equations of the bifurcation domain boundary and unstable stress direction cones are established. Diffuse failure is simulated numerically by perturbing bifurcation states.Différents modes de rupture reliés à différents types de bifurcations apparaissent dans des matériaux élasto-plastiques non-associés tels que les géomatériaux. Après avoir présenté quelques résultats expérimentaux typiques, cette question est abordée au moyen de relations constitutives phénoménologiques et de simulations numériques directes basées sur la méthode des éléments discrets. Le critère du travail du second ordre lié aux modes de rupture diffuse est particulièrement étudié dans le cadre de la mécanique des milieux continus et des milieux discrets. Les équations des limites du domaine de bifurcation et des cônes de directions de contrainte instables sont établies. La rupture diffuse est simulée numériquement par des perturbations des états de bifurcation

Buckling and free vibration analysis of laminated composite plates using an efficient and simple higher order shear deformation theory

In this paper, the buckling and free vibration analysis of laminated composite plates using an efficient and simple higher order shear deformation theory are examined by using a refined shear deformation theory. This theory is based on the assumption that the transverse displacements consist of bending and shear components where the bending components do not contribute to shear forces, and likewise, the shear components do not contribute to bending moments. The most interesting feature of this theory is that it allows for parabolic distributions of transverse shear stresses across the plate thickness and satisfies the conditions of zero shear stresses at the top and bottom surfaces of the plate without using shear correction factors. The number of independent unknowns in the present theory is four, as against five in other shear deformation theories. In this analysis, the equations of motion for simply supported thick laminated rectangular plates are derived and obtained through the use of Hamilton’s principle. The closed-form solutions of anti-symmetric cross-ply and angle- ply laminates are obtained using Navier solution. Numerical results of the present study are compared with three-dimensional elasticity solutions and results of the first-order and the other higher-order theories reported in the literature. It can be concluded that the proposed theory is accurate and simple in solving the buckling and free vibration behaviors of laminated composite plates