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Influence of the virtual strain rate of noncohesive granular media on the discrete element method
Kiichi Suzuki, 2015, izvirni znanstveni članek

Opis: The discrete element method (DEM) is an alternative computational tool for augmenting laboratory experiments because of its advantages in detailing macro- and micro-mechanical information. However, it should be noted that the DEM does not usually consider the convergence for each time step, because of the necessity for a huge calculation time. In that case, it indicates that the uniqueness of the solution is not guaranteed, except in the case of a very small strain rate, even though the behavior looks qualitatively reasonable. At first, the influence of strain rate among numerically imaginary input parameters for a non-cohesive material was investigated for monotonic, biaxial shear tests. Then, new findings were obtained from the DEM simulations. Strain rate has a significant influence on the shear behavior, especially after the peak strength of dense specimens. A quasi-static steady state exists, not a static steady state. The “strong” fabric ratio is closely related to the stress ratio. The maximum slip coordination number occurs around the phase-transformation ratio and the shear band appears around the peak strength.
Ključne besede: discrete element method, DEM, induced anisotropy, quasi-static steady state, strain rate, uniqueness
Objavljeno v DKUM: 14.06.2018; Ogledov: 1144; Prenosov: 220
Celotno besedilo (690,97 KB)
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A comparison between conventional triaxial and plane-strain compression on a particulate system using 3D DEM
Mahmud Sazzad, Kiichi Suzuki, 2012, izvirni znanstveni članek

Opis: Granular materials such as sand are subjected to different stress paths depending on the in-situ conditions. For example, a granular system under the foundations experiences conventional triaxial compression (CTC), while it experiences plane-strain compression (PSC) in the case of the embankment of roads. Due to the difference in the stress paths, the behavior of granular materials also becomes different. This paper aims at comparing the behavior of granular materials under CTC and PSC conditions using the 3D discrete-element method (DEM). An isotropically compressed dense sample consisting of 8000 spheres was prepared numerically using periodic boundaries. The CTC and PSC tests were simulated using the same isotropically compressed dense sample to compare and explore the macro- and micro-mechanical responses of granular materials without any bias from the initial fabric of the numerical sample. Qualitatively, the simulated stress-strain responses are consistent with that observed in the experimental studies. The dilatancy index is found to be independent of the stress paths used in the present study. The b value (defined as b = (σ2 − σ3)/(σ1 − σ3) where σ1, σ2 and σ3 are the stresses in the x1 -, x2 - and x3 - directions, respectively) - axial strain curve has a close similarity with the stress ratio - axial strain curve for the PSC test. The evolution of the coordination number and the sliding contact fraction is independent of the stress paths. A link between the macro- and micro-quantities is observed and a unique macro-micro relationship is noticed, regardless of the stress paths applied in this study.
Ključne besede: conventional triaxial compression, plane-strain compression, micro response, DEM
Objavljeno v DKUM: 13.06.2018; Ogledov: 1237; Prenosov: 66
Celotno besedilo (257,70 KB)
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