Effects of polydispersity on the micro–macro behavior of granular assemblies under different deformation paths  

作　　者：Nishant Kumar Olukayode I.Imole Vanessa Magnanimo Stefan Luding 

机构地区：[1]Multi Scale Mechanics(MSM), Faculty of Engineering Technology, MESA+, University of Twente

出　　处：《Particuology》2014年第1期64-79,共16页颗粒学报（英文版）

基　　金：financially supported by the European Union funded Marie Curie Initial Training Network,FP7(ITN-238577)

摘　　要：The micromechanical and macromechanical behavior of idealized granular assemblies, made by linearly elastic, frictionless, polydisperse spheres, are studied in a periodic, triaxial box geometry, using the dis crete element method. Emphasis is put on the effect of polydispersity under purely isotropic loading and unloading, deviatoric （volume conserving）, and uniaxial compression paths. We show that scaled pressure, coordination number and fraction of rattlers behave in a very similar fashion as functions of volume fraction, irrespective of the deformation path applied. Interestingly, they show a systematic dependence on the deformation mode and polydispersity via the respective jamming volume fraction. This confirms that the concept of a single jamming point has to be rephrased to a range of variable jamming points, dependent on microstructure and history of the sample, making the jamming volume fraction a statevariable. This behavior is confirmed when a simplified constitutive model involving structural anisotropy is calibrated using the purely isotropic and deviatoric simulations. The basic model parameters are found to depend on the polydispersity of the sample through the different jamming volume fractions. The predictive power of the calibrated model is checked by comparison with an independent test, namely uniaxial compression. The important features of the uniaxial experiment are captured and a qualitative prediction for the evolution of stress and fabric is shown involving a ＂softening＂ regime in both stress and fabric stronger for the latter that was not prescribed into the model a priori.The micromechanical and macromechanical behavior of idealized granular assemblies, made by linearly elastic, frictionless, polydisperse spheres, are studied in a periodic, triaxial box geometry, using the dis crete element method. Emphasis is put on the effect of polydispersity under purely isotropic loading and unloading, deviatoric （volume conserving）, and uniaxial compression paths. We show that scaled pressure, coordination number and fraction of rattlers behave in a very similar fashion as functions of volume fraction, irrespective of the deformation path applied. Interestingly, they show a systematic dependence on the deformation mode and polydispersity via the respective jamming volume fraction. This confirms that the concept of a single jamming point has to be rephrased to a range of variable jamming points, dependent on microstructure and history of the sample, making the jamming volume fraction a statevariable. This behavior is confirmed when a simplified constitutive model involving structural anisotropy is calibrated using the purely isotropic and deviatoric simulations. The basic model parameters are found to depend on the polydispersity of the sample through the different jamming volume fractions. The predictive power of the calibrated model is checked by comparison with an independent test, namely uniaxial compression. The important features of the uniaxial experiment are captured and a qualitative prediction for the evolution of stress and fabric is shown involving a ＂softening＂ regime in both stress and fabric stronger for the latter that was not prescribed into the model a priori.

关 键 词：POLYDISPERSITY ANISOTROPY Deformations Calibration PARDEM 

分 类 号：TQ021[化学工程]