Rheology of dense granular suspensions under extensional flow
Rheology of dense granular suspensions under extensional flow
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DOI：
10.1122/1.5004007
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发表时间：
2018-01
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影响因子：
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通讯作者：
O. Cheal;C. Ness
中科院分区：
文献类型：
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作者：
O. Cheal;C. Ness
我们用数值模拟的方法研究了不同拉伸变形和简单剪切作用下的颗粒悬浮液。粘度和Trouton比(拉伸粘度与剪切粘度之比)被计算为接近零惯性极限的固体体积分数的函数。无摩擦粒子的悬浮遵循牛顿Trouton比率，一直到与变形类型无关的普遍干扰点。相反，摩擦颗粒导致了与变形类型有关的阻塞分数，这对剪切流来说是最大的。因此，Trouton的比率从牛顿开始，但偏离为$Phi到Phi_m$。我们通过考虑干扰时的粒子排列来解释摩擦粒子悬浮中的这种差异。虽然无摩擦颗粒悬浮液在堵塞时具有近乎各向同性的微观结构，但摩擦允许更多的各向异性接触链，从而允许在较低的pH下进行堵塞，但会引入协议依赖性。最后，我们提供了粘性数流变学可以从剪切变形扩展到伸展变形的证据，其中对于无摩擦颗粒的崩塌尤其成功。拉伸变形是悬浮液中一类重要的流变性，与浆体加工、造粒和高性能材料有关。
We study granular suspensions under a variety of extensional deformations and simple shear using numerical simulations. The viscosity and Trouton's ratio (the ratio of extensional to shear viscosity) are computed as functions of solids volume fraction $\phi$ close to the limit of zero inertia. Suspensions of frictionless particles follow a Newtonian Trouton's ratio for $\phi$ all the way up to $\phi_0$, a universal jamming point that is independent of deformation type. In contrast, frictional particles lead to a deformation-type-dependent jamming fraction $\phi_m$, which is largest for shear flows. Trouton's ratio consequently starts off Newtonian but diverges as $\phi\to\phi_m$. We explain this discrepancy in suspensions of frictional particles by considering the particle arrangements at jamming. While frictionless particle suspensions have a nearly isotropic microstructure at jamming, friction permits more anisotropic contact chains that allow jamming at lower $\phi$ but introduce protocol dependence. Finally, we provide evidence that viscous number rheology can be extended from shear to extensional deformations, with a particularly successful collapse for frictionless particles. Extensional deformations are an important class of rheometric flow in suspensions, relevant to paste processing, granulation and high performance materials.