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• Physique/Matière Condensée/Matière Molle
  
• Sciences de l'ingénieur/Matériaux
  
• Physique/Matière Condensée/Systèmes désordonnés et réseaux de neurones
  
• Sciences de l'ingénieur/Mécanique/Mécanique des fluides
  
• Sciences de l'ingénieur/Mécanique
  
• Physique/Astrophysique
  
• Physique/Astrophysique/Planétologie et astrophysique de la terre [astro-ph.EP]
  
• Sciences de l'ingénieur/Mécanique/Mécanique des solides
  
• Physique
  
• Sciences de l'ingénieur
  
• Physique/Mécanique/Mécanique des matériaux
  
• Physique/Mécanique/Mécanique des solides
  
• Sciences de l'ingénieur/Génie civil/Géotechnique
  
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• Sciences de l'ingénieur/Mécanique/Génie mécanique
  
• Physique/Mécanique/Génie mécanique
  

We study the crushing strength of brittle materials whose internal structure (e.g., mineral particles or grains) presents a layered arrangement reminiscent of sedimentary and metamorphic rocks. Taking a discrete-element approach, we probe the failure strength of circular-shaped samples intended to reproduce specific mineral configurations. To do so, assemblies of cells, products of a modified Voronoi tessellation, are joined in mechanically-stable layerings using a bonding law. The cells’ shape distribution allows us to set a level of inherent anisotropy to the material. Using a diametral point loading, and systematically changing the loading orientation with respect to the cells’ configuration, we characterize the failure strength of increasingly anisotropic structures. This approach lets us reproduce experimental observations regarding the shape of the failure strength curve, the Weibull modulus, failure patterns of rocks, and quantify the consumption of the fragmentation energy, and the induced anisotropies linked to the cell’s geometry and force transmission in the samples. Based on a fine description of geometrical and mechanical properties at the onset of failure, we develop a micromechanical breakdown of the crushing strength variability using an analytical decomposition of the stress tensor and the geometrical and force anisotropies. We can conclude that the origins of failure strength in anisotropic layered media rely on compensations of geometrical and mechanical anisotropies, as well as an increasing average radial force between minerals indistinctive of tensile or compressive components.

This paper analyzes the compaction behavior of assemblies composed of soft (elastic) spherical particles beyond the jammed state, using three-dimensional non-smooth contact dynamic simulations. The assemblies of particles are characterized using the evolution of the packing fraction, the coordination number, and the von Misses stress distribution within the particles as the confining stress increases. The packing fraction increases and tends toward a maximum value close to 1, and the mean coordination number increases as a square root of the packing fraction. As the confining stress increases, a transition is observed from a granular-like material with exponential tails of the shear stress distributions to a continuous-like material characterized by Gaussian-like distributions of the shear stresses. We develop an equation that describes the evolution of the packing fraction as a function of the applied pressure. This equation, based on the micromechanical expression of the granular stress tensor, the limit of the Hertz contact law for small deformation, and the power-law relation between the packing fraction and the coordination of the particles, provides good predictions from the jamming point up to very high densities without the need for tuning any parameters.

The compaction behavior of deformable grain packings beyond jamming is a process widelyinvestigated because of its great industrial and engineering significance, yet it remainsmisunderstood. Many numerical and experimental approaches have enabled the explorationof the physics of deformable granular media and the definition of some theoretical modelswith reliable predictions for the relations between pressure and density. However, thesemodels have some limitations such as the use of nonphysical parameters, the lack of accuracyat extreme pressures, and the missing physical derivation of the compaction equations. Westudy the compaction behavior of soft sphere packings beyond the jammed state by numericalsimulations (see Fig. 1) using the non-smooth contact dynamic method. The resultsshow that the evolution of packing fraction - as a function of the applied pressure - is welldescribed using only micromechanical parameters. This is obtained based on the stress tensor,together with the limit too small deformation of the particles' strain. Our work also suggeststhat it is possible to extrapolate the compaction behavior of an elementary Voronoi cell thatcontains a single particle to the packing scale.

Granular column collapse simulations are a benchmark in the study of transitional granular flows [1].The column collapse is a simplified version of occurring flows in highly varying scales, ranging innatural debris flows or industrial handling purposes. A characteristic among them is their occasionalsubmergence in a viscous fluid, resulting in strong grain-fluid interactions between particles ofdifferent sizes [2, 3, 4]. This work studies the effect of polydispersity in the runout of the collapse ofimmersed granular columns. For this purpose, we simulate a two-dimensional immersed granularcolumn employing a coupled discrete and finite element fluid model (DEM-FEM) [5]. In thisconfiguration, we study granular systems with different grain size distributions (GSD), varying theratio between the biggest and smallest particle from 1.2 to 10. We simulate dense granular columns,varying the initial column height H0 and initial column width L0 through three different aspect ratiosA = H0/L0 = (0.5, 1.0, 3.5). We show that the collapse mechanism and collapse duration stronglydepend on polydispersity. Increasing polydispersity reduces the kinematic energy of the collapse andreduces the final runout. For short columns A = (0.5, 1.0), the repose angle increases with thepolydispersity until it reaches a plateau near 17°. Our results highlight the effect on the final shape,flow mechanism, and fluid-grain interaction of increasing polydispersity in transitional immersedflows.

Size limitations of geotechnical testing equipment often require that samples of coarse granular materials have to be scaled in order to be tested in the laboratory. Scaling implies a convenient modification of the particle size distribution (PSD) to reduce particle sizes. However, it is well known that particle size and shape may be correlated in nature, due to geological factors (as an example). By means of two-dimensional contact dynamics simulations, we analyzed the effect of altering the size span on the shear strength of granular materials when particle size and shape are correlated. Two different systems were considered: one made of only circular particles, and the second made of size-shape correlated particles. By varying systematically the size span we observed that the resulting alteration of material strength is not due to the change in particle sizes. It results instead from the variation of the particle shapes induced by the modification of the PSD, when particle size and particle shape are correlated. This finding suggests that particle shape distribution is a higher order factor than PSD for the shear strength of granular materials. It also highlights the importance of particle shape quantification in soil classification and the case for its consideration in activities such as sampling, subsampling, and scaling of coarse materials for geotechnical testing