Pre-peak deformation of model granular materials: a DEM study. In : Geomechanics from micro to macro


Type de document
Résumé / Abstract
Initial states of granular assemblies, which determine the response to quasi-statically applied deviator stresses in mechanical tests, are usually classified according to their density and structural anisotropy. Discrete simulations (DEM) of model granular materials (spherical bead packs) reveal however that dense assemblies with isotropic fabric can be prepared with very different coordination numbers, ranging from 4 to 6 under low confining stress. When subsequently subjected to triaxial compression tests equally dense systems differing by their coordination number have the same peak strength, but strongly differ in their pre-peak stress-strain response. Well-coordinated systems have contact networks that tend to resist throughout large deviator intervals, and exhibit a stiff response, with a global stiffness scaling with the contact stiffness (type I strains). Poorly coordinated ones essentially deform in a series of microscopic instabilities in which contact networks get continuously broken and repaired (type II strains). The distinction between strains of types I and II (not to be confused with elastic and plastic strains) has important consequences in terms of sensitivities of macroscopic response to micromechanical features and propensity to develop localization instabilities. The coordination number, which determines to a large extent the type (I or II) of the response, can be related to initial elastic moduli. These observations call for changes in the practice of DEM approaches and refinements in the classification of internal states and stress-strain behaviour of granular materials. Some experimental confrontations are possible.
Taylor & Francis Ltd ; CRC Press

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