Singh Abhinendra, Magnanimo Vanessa, Saitoh Kuniyasu, Luding Stefan
Multi Scale Mechanics (MSM), Faculty of Engineering Technology, MESA+, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Aug;90(2):022202. doi: 10.1103/PhysRevE.90.022202. Epub 2014 Aug 6.
Cohesive powders have widely different bulk behavior due to their peculiar interactions. We use discrete element simulations to investigate the effect of contact cohesion on the steady state flow of dense powders in a slowly sheared split-bottom Couette cell, which imposes a wide stable shear band. The intensity of cohesive forces can be quantified by the granular Bond number (Bo), namely the ratio between maximum attractive force and average force due to external compression. We find that the shear banding phenomenon is almost independent of cohesion for Bond numbers Bo<1, however for Bo≥1 cohesive forces start to play an important role, as both width and center position of the band increase. Inside the shear band, the mean normal contact force is independent of cohesion and depends only on the confining stress. In contrast, when the behavior is analyzed focusing on the eigendirections of the local strain rate tensor, a dependence on cohesion shows up. Forces carried by contacts along the compressive and tensile directions are symmetric about the mean force (larger and smaller respectively), while the force along the third, neutral direction follows the mean force. This anisotropy of the force network increases with cohesion, just like the heterogeneity in all (compressive, tensile and neutral) directions.
由于其特殊的相互作用，粘性粉末具有广泛不同的堆积行为。我们使用离散元模拟来研究接触粘性对在缓慢剪切的分体底部库埃特单元中致密粉末稳态流动的影响，该单元会形成一个宽的稳定剪切带。粘性力的强度可以通过颗粒键数（Bo）来量化，即最大吸引力与外部压缩引起的平均力之比。我们发现，对于键数Bo<1，剪切带现象几乎与粘性无关，然而对于Bo≥1，粘性力开始发挥重要作用，因为带的宽度和中心位置都会增加。在剪切带内，平均法向接触力与粘性无关，仅取决于围压。相反，当关注局部应变率张量的特征方向来分析行为时，会出现对粘性的依赖性。沿压缩和拉伸方向的接触力相对于平均力是对称的（分别更大和更小），而沿第三个中性方向的力则遵循平均力。力网络的这种各向异性随着粘性的增加而增加，就像在所有（压缩、拉伸和中性）方向上的不均匀性一样。
