Scale separation between grain detachment and grain transport in granular media subjected to an internal flow

Abstract

Based on a discrete element method (DEM), this paper investigates the basic mechanisms and the associated scales related to grain detachment and grain transport processes at stake in widely graded poly-disperse assemblies of spheres subjected to internal fluid flows. From the identification of force chains, particles sensitive to grain detachment are identified. Based on the computation of autocorrelation lengths, a typical length scale associated with this phenomenon is then defined. From the characterization of the void space as a pore network, particles eligible for grain transport are identified among the detachable particles. Based on the definition of a mean travel distance, the typical length scale associated with grain transport is finally characterized. The comparison between the two length scales highlights a scale separation between grain detachment and grain transport.

Micro‐inertia origin of instabilities in granular materials

“…Thanks to the combine use of photoelastic grains and numerical simulations, the overall behavior of granular materials was shown to rely on a limited number of grains organized in mesostructures called force chains . Following the definition as well as the algorithm given in Peters et al, recent results highlighted the importance of these mesoscale structures with respect to the overall mechanical properties of the granular materials . In particular, it has been shown that the strength of a granular material results from its ability to build relatively long force chains and its ability to constantly rearrange existing ones to cope with any change in the boundary conditions.…”

“…Now commonly used in the literature, the force chain concept provides a relevant mesoscopic scale to account for the macroscopic mechanical behavior of granular materials . In particular, it has been shown that the strength of a granular material results from its ability to build relatively long force chains and to constantly rearrange the existing force chains to cope with any change in the boundary conditions .…”

“…Now commonly used in the literature, the force chain concept provides a relevant mesoscopic scale to account for the macroscopic mechanical behavior of granular materials . In particular, it has been shown that the strength of a granular material results from its ability to build relatively long force chains and to constantly rearrange the existing force chains to cope with any change in the boundary conditions . Details on the algorithm used to identify the chained particles of a sample can be found in Peters et al The definition of a force chain used throughout this manuscript is briefly reviewed: The particles belonging to a force chain have a higher principal stress than the mean particle principal stress. The principal stress direction of chained particles is aligned with the geometrical contact direction (less than 45° deviation). A force chain contains at least 3 contacting particles. …”

“…The input parameters used in this elasto-frictional contact law are reported in Table 1. They are chosen equal to those of Hadda et al 15 and Wautier et al 24 After computing all inter-particle contact forces, the induced particles displacements are integrated based on Newton's second law of motion using the DEM open source code YADE. 28…”

“…[17][18][19][20][21] Following the definition as well as the algorithm given in Peters et al, 22 recent results highlighted the importance of these mesoscale structures with respect to the overall mechanical properties of the granular materials. [23][24][25] In particular, it has been shown that the strength of a granular material results from its ability to build relatively long force chains and its ability to constantly rearrange existing ones to cope with any change in the boundary conditions. In addition, as shown by Zhu et al 23,26 and Tordesillas et al 25 in 2D, for instance, the particles not included in these chains forms cycles that have an important stabilizing role.…”