Abstract
DEM-simulated model cohesive assemblies of spherical grains of diameterd, with contact tensile strengthF0, once prepared in loose states, are quasistatically subjected to growing isotropic pressureP, and then to triaxial compression, maintaining lateral stresses σ2= σ3=Pwhile increasing axial stress σ1=P+qand strain є1. Reduced pressureP*=d2P/F0varies from 0.1 (cohesion dominated case, for which systems typically equilibrate with solid fraction Ф ≃ 0.35), to large values for which the cohesionless behavior is retrieved. In triaxial compression, while the moderate strain response (є1~ 0.1) is influenced by initial coordination numbers and mesoscale heterogeneities, the approach to the critical state, as bothq(deviator) and Ф steadily increase, gets slower for smallerP*. Critical ratioq/P strongly increases for decreasingP*, as roughly predicted in an “effective stress” scheme. Anomalously small elastic moduli are observed in the gel-like structures. While extensive geometric rearrangements take place, no shear banding is observed. Loose cohesive granular assemblies are thus capable of large quasistatic stable plastic strains and ductile rupture.
Highlights
Numerical grain-level investigations, by discrete element methods (DEM)[1], of the properties of assemblies of hard objects interacting by frictional contacts [2] are quite widespread, and their quasistatic mechanical behavior, as probed, e.g., by the standard triaxial test used in geotechnique labs with sands [3], is often addressed
Cohesive granular assemblies exhibit a wider variety of structures and properties, and the present communication contributed to the investigation of the little known open, loose systems, with lower reduced pressure P⇤ than in most published studies [12]
We showed the enduring e↵ect of the initial geometry for the same density, in isotropic or triaxial compression
Summary
Numerical grain-level investigations, by discrete element methods (DEM)[1], of the properties of assemblies of hard objects interacting by frictional contacts [2] are quite widespread, and their quasistatic mechanical behavior, as probed, e.g., by the standard triaxial test used in geotechnique labs with sands [3], is often addressed. Cohesive granular assemblies, such as powders and colloids, are less frequently studied, but exhibit a wider variety of static states.
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