堆石料颗粒破碎强度的尺寸和形状效应隐式离散元研究

Implicit DEM analyses of size and shape effects on crushing strength of rockfill particles

采用隐式离散元法(DEM),亦称非光滑接触动力学(NSCD)法,模拟了堆石料单颗粒的一维压缩破碎过程。采用多面体颗粒近似真实堆石料颗粒的不规则棱角状形状,并通过Voronoi空间划分将母颗粒离散成若干多面体子颗粒,子颗粒间通过接触面上的内聚力模型(CZM)胶结发生相互作用,胶结断裂则可反映颗粒的破碎过程,可避免传统DEM中常用的碎片替代法和胶结小球法的缺点。首先使用巴西劈裂试验获得CZM参数,其后开展了不同粒径颗粒的一维压缩试验,结果表明颗粒破碎强度服从Weibull分布,且破碎强度大小和变异性均随着颗粒尺寸的增大而减小。还进一步模拟了不同形状颗粒的压缩试验,发现颗粒形状与加载方向均对颗粒破碎强度有显著影响。长轴方向加载破碎强度通常最低,且在相同等效粒径下,球状、椭球状、扁平状颗粒的平均破碎特征强度依次降低。

An implicit version of discrete element method(DEM)called non-smooth contact dynamics(NSCD)is used to simulate the crushing process of single rockfill particle under one-dimensional(1D)compression.The angular and irregular shapes of rockfill particles are represented using polyhedrons,which are discretized into smaller elementary cells through the Voronoi tessellation.The interaction between neighboring elementary cells is described by the cohesive zone model(CZM),where hybrid tensile and shear failure modes are considered.Consequently,particle crushing can be captured by the breakage of CZM bonds subjected to external loading.The proposed method for modeling the particle crushing avoids drawbacks of the traditional fragment replacement method and bonded sphere method in DEM.The Brazilian splitting tests on granite are performed to calibrate the parameters for CZM.1D compression tests on single particles with different sizes and shapes further reveal that the crushing strength of particles follows the Weibull distribution,and both the magnitudes and the variances decrease with the increasing particle size.For the particles with different principal axes(e.g.,elongated and platy),the crushing strength loaded in the major axis is the smallest among all directions.It is also shown that the elongated and platy particles have smaller average strength than the spherical ones given the same equivalent particle size.