Bond rolling resistance and its effect on yielding of bonded granulates by DEM analyses

A discrete element modelling of bonded granulates and investigation on the bond effect on their behaviour are very important to geomechanics. This paper presents a two-dimensional (2-D) discrete element theory for bonded granulates with bond rolling resistance and provides a numerical investigation into the effect of bond rolling resistance on the yielding of bonded granulates. The model consists of mechanical contact models and equations governing the motion of bonded particles. The key point of the theory is that the assumption in the original bond contact model previously proposed by the authors (55th CSCE-ASCE Conference, Hamilton, Out., Canada, 2002: 313-320: J. Eng. Mech. (ASCE) 2005: 131(11):1209-1213) that bonded particles are in contact at discrete points. is here replaced by a more reliable assumption that bonded particles are in contact over a width. By making the idealization that the bond contact width is continuously distributed with the normal/tangential basic elements (BE) (each BE is composed of spring. dashpot, bond, slider or divider), We establish a bond rolling contact model together with bond normal tangential contact models. and also relate the governing equations to local equilibrium. Only one physical parameter beta needs to be introduced in the theory in comparison to the original bond discrete element model. The model has been implemented into a 2-D distinct element method code. NS2D. Using the NS2D, a total of 86 1-D. constant stress ratio. and biaxial compressions tests have been carried out oil the bonded granular samples of different densities. bonding strengths and rolling resistances. The numerical results show that: (i) the new theory predicts a larger internal friction angle. a larger yielding stress. more brittle behaviour and larger final broken contact ratio than the original bond model: (ii) the yielding stress increases nonlinearly with the increasing value of beta. and (iii) the first-yield curve (initiation of bond breakage), which define a zone of none bond breakage and which shape and size are affected by the material density, is amplified by the bond rolling resistance in analogous to that predicted by the original bond model. Copyright (C) 2006 John Wiley & Sons, Ltd.