椭球颗粒体系宏、细观特性的3维离散元分析

Macro and Micro-behaviors of Ellipsoidal Particle System Using 3D DEM Simulation

颗粒材料由大量不同形状的离散颗粒组成,其力学特性与构成颗粒体系的颗粒形状密切相关。目前,关于颗粒形状对颗粒材料剪切强度的影响已有大量的物理试验或数值模拟试验研究,而非球形颗粒材料在复杂应力路径下的宏、细观力学特性认识还不够充分。本文采用离散单元法(DEM)对按一定级配生成的不同伸长率的椭球颗粒体系进行等σ_(3)(第3主应力)及等b(中主应力比)的真三轴加载数值模拟试验,研究椭球颗粒体系的3维宏、细观力学特性,并验证常用3维强度准则对椭球颗粒体系的适用性。结果表明:在3维加载路径下,不同于圆球颗粒体系宏、细观演化规律的一致性,椭球颗粒体系的宏观应力面与细观组构面演化规律不一致,宏观应力比与强接触网络组构偏值/均值比线性不为1,这是因为椭球颗粒体系弱接触网络对宏观应力的贡献;椭球颗粒体系宏观体应变、细观法向接触力分布、接触数目及配位数分布等宏、细观指标与加载路径无关;随着椭球伸长率LAR增大,Mohr–Coulomb准则、Lade–Duncan准则、Mastsuoka–Nakai准则及施维成3维强度准则对φ_(max)(峰值内摩擦角)–b关系预测准确度逐渐增大,其中,Lade–Duncan准则能更好地拟合不同加载路径下椭球颗粒体系的数据点。研究为真实应力状态下椭球颗粒材料的宏、细观特性的认识提供了一定的理论基础。

Granular materials are composed of a large number of discrete particles with different particle shapes,and their mechanical properties are closely related to the particle shape of the particle system.At present,the macro and micro properties of non-spherical granular materials under complex stress paths are not fully understood.A series of constant-σ_(3)constant-b true triaxial tests on ellipsoid particle systems with a certain gradation was carried out utilizing the discrete element method(DEM),and the aspect ratio of ellipsoid particles AR was changed to reflect the effects of particle shape on the macro-mechanical properties,and the applicability of the commonly used three-dimensional strength criteria to the ellipsoid particle system was verified.The results showed that under the three-dimensional loading path,different from the consistency of the macro and micro evolution laws of the spherical particle system,the evolution laws of the macro stress surface and the micro fabric surface of the ellipsoidal particle system were inconsistent,and the linear relationship between the macro stress ratio and the partial value vs mean value ratio of the strong contact network fabric was not 1,which was attributed to the contribution of the weak contact network of the ellipsoidal particle system to the macro stress.The macroscopic strain and microscopic characteristics of the ellipsoid particle system were independent of the loading paths,such as normal contact force distribution,contact number,and coordination number distribution.In addition,the four of the three-dimensional strength criteria had better prediction capability when AR was larger,especially for Lade-Duncan criteria.The research provides a theoretical basis for improving understanding of the macro and micro properties of ellipsoidal granular materials under real stress states.