基于离散元法的长短轴之比对散粒材料抗剪强度影响分析

杆状颗粒由于其形状与砾石、药品和谷物等真实颗粒的形状接近而受到研究者们的关注,其形状特征常用长短轴之比进行表征.以往许多学者曾通过离散元法研究过在相同孔隙率下杆状颗粒长短轴之比对其抗剪强度的影响,但在相同相对密度下的研究并不多见.通过控制颗粒摩擦因数形成具有相同相对密度的试样,研究了0%、35%、65%及100%相对密度下颗粒的长短轴之比对试样抗剪强度的影响规律.另外,还进行了相同孔隙率下的试验以进行结果对比.研究结果表明,相同相对密度下,峰值状态和临界状态时试样剪应力随长短轴之比增大而增大,与相同孔隙率下的结果一致,但峰值剪应力增大幅值要比相同孔隙率下的小.另外,对不同长短轴之比下试样内摩擦角进行分析,发现临界状态时内摩擦角随长短轴之比增大而增大,而峰值状态时内摩擦角受长短轴之比的影响相对较小.最后从试样剪胀性方面进行了分析,阐述了以上现象发生的机理.

Analysis of effect of aspect ratio on shear strength of granular materials based on DEM

The elongated particles have attracted much attention from academic interests because their particle shapes are similar to many real particles (e.g., gravels, pills and grains). The shape of elongated particles can be characterized by aspect ratio. Many researchers have studied the effect of aspect ratio on shear strength of elongated particles at a constant porosity based on discrete element method (DEM). However, the research on a constant relative density is limited. The effect of aspect ratio on shear strength of elongated particles is studied at 0%, 35%, 65% and 100% relative density. The constant relative density of assemblies is formed by adjusting the friction factor of particles. Alternatively, the numerically direct shear tests at a constant porosity are also conducted in order to compare the results with those at a constant relative density. The test results indicate that increased aspect ratio leads to increase of the shear stress at peak state and critical state at a constant relative density, and this trend is consistent with the result at a constant porosity. However, the increased value of peak shear stress at a constant relative density is much smaller than that at a constant porosity. Furthermore, the angles of internal friction of assemblies with different aspect ratios are analyzed. It is found that increased aspect ratio leads to increase of the angle of internal friction at critical state, whereas increased aspect ratio has relatively small influence on the angle of internal friction at peak state. The aforementioned phenomena are explained by analyzing the dilatancy of assemblies.