HE Jinlong¹ ，YANG Yang² ，LIU Xiaoxing^2，3

1. SINOPEC Research Institute of Petroleum Processing Co. ， Ltd. ， Beijing 100083， China；

2. State Key Laboratory of Mesoscience and Engineering， Institute of Process Engineering， Chinese Academy of Sciences， Beijing 100190， China；

3. School of Chemical Engineering， University of Chinese Academy of Sciences， Beijing 100049， China

Abstract

Objective The four main criteria for particle breakage are the mean principal stress， maximum principal stress， maximum shear stress， and maximum contact force. Currently， there is no consensus on which particle breakage criterion is more reasonable. The aim of this study is to assess the applicability of these four particle breakage criteria and to discuss the possible reasons for the inconsistent conclusions reported in the literature.

Methods Based on a self-developed （discrete element method） DEM program， the critical state of macroscopic particles was evaluated by simulating the breakage of aggregate samples. To simulate arbitrary loading configuration， particle materials were first prepared through gravitational deposition. For a given number of loading points， particles with the same number of contacts were randomly selected from the material and replaced with aggregates. The surrounding particles were then moved centripetally to apply compressive loading. In this study， uniaxial， biaxial， and triaxial loading tests were also conducted to investigate the critical state of aggregates under specific loading configurations.

Results The DEM simulation results demonstrated that the mean principal stress and maximum principal stress at the moment of aggregate breakage varied with the number of loading points， regardless of whether the loading configuration was random or predetermined. The simulation results for the random loading configuration suggested that the average maximum shear stress and maximum contact force were approximately independent of the number of loading points. However， the simulation results for the predetermined loading configuration showed that these two parameters were related to the number of loading points， indicating that the maximum shear stress and maximum contact force were influenced by both the number and spatial arrangement of the loading points. The uniaxial compression results of the disc-shaped aggregate samples revealed that， in the direction perpendicular to the loading axis， tensile stress concentrations formed at the inner edge of the damaged region， leading to tensile failure of the sample. The result suggested that the effect of loading points on the critical state of particles originated from the confining pressure effect.

Conclusion The DEM simulation results demonstrate that none of the four investigated breakage criteria can uniquely determine the critical state of particles under loading. Therefore， to develop a particle breakage criterion based on these four parameters，the influence of loading configuration should be properly accounted for.

Keywords：particle crushing breakage； breakage criterion； multi-point loading； uniaxial loading； discrete element method