基于颗粒流模型的颗粒材料宏-细观力学研究

基于颗粒流模型对各向同性和落雨法两种不同初始状态的颗粒材料细观参数和应力进行研究,建立了细观组构、接触力、主应力比之间的表达式。通过数值离散元程序模拟了上述两种不同初始状态钢珠的室内三轴试验。结果表明:两者应力应变曲线基本一致;各向同性试样组构初始为均匀分布的球体,落雨法试样初始组构略呈椭球体,随着加载两种试样内颗粒配位数先增加后减小,水平面内和竖直面内组构减少且面内主轴发生偏转,试样破坏后的组构张量表现为花生状椭球体;法向接触力张量表现出与组构变化相似的规律,宏观上接触力的影响数值上大于组构张量,试样破坏后法向接触力张量空间分布呈现出更明显的两端和水平面内凹陷的花生状椭球体,且面内主轴有偏转。由莫尔库仑准则得出颗粒材料内摩擦角与组构、接触力细观参数表达式,并进行了验证,因此,可通过细观参数得出颗粒材料宏观内摩擦角。

Macro-mesoscopic mechanical behaviors of granular material based on particle flow model

Based on particle flow model, the mesoscopic parameters and stress of two different granular material, isotropy and dry deposition method specimens, were studied, and the expression of mesoscopic fabric tensor, contact force and principal stress ratio is derived. Through numerical discrete element program, the triaxial test of above two different initial condition of steel ball was simulated. The results show that the obtained stress-strain curve was similar; the fabric tensor of initial isotropic specimen is a sphere of uniform distribution, and the initial fabric tensor of dry deposition method specimen is an ellipsoid; with the increase of loading, the particle coordination number in two specimen increase first and then decrease, and also the fabric within horizontal and vertical planes is decreased and the in-plane principal axis is deflected, after the specimen is damaged, the fabric tensor of specimen is in a peanut-shape ellipsoid; the normal contact force rule is similar to fabric tensor and its influence is larger than the fabric tensor from the macroscopic view; after the specimen is damaged, the normal contact force tensor is a more obvious peanut-shape ellipsoid and in-plane principal axis also shows deflection. The internal friction angle expression including fabric, contact force mesoscopic parameters is obtained by Mohr-Coulomb criterion, and its validity is verified. Therefore, the granular material internal friction angle formula could be obtained by mesoscopic parameters. 