论文标题
在施加压力下密集悬浮液的振荡剪切流：流变和微结构
Oscillatory shear flows of dense suspensions at imposed pressure: Rheology and micro-structure
论文作者
论文摘要
振荡性剪切被广泛用于研究不稳定剪切下悬浮液的流变特性。此外，最近的作品表明振荡流可以改善密集悬浮液的流动性。尽管大多数研究都是在恒定体积下进行的，但在这里我们研究了使用正常压力控制设置的二维悬架的振荡剪切流。为了表征流变学，我们介绍了一个复杂的宏观摩擦系数$μ^{*} $，遵循复杂粘度$η^{*} $的约定，又是剪切速率平均粘性数字$ j'$。通过系统地使用数值模拟来研究应变量级$γ_0$和$ j'U $，研究了密集悬浮液的流变学和微观结构。我们研究了由摩擦（$μ_p= 0.4 $）或无摩擦（$μ_p= 0 $）粒子组成的悬浮液，并发现复杂的宏观摩擦和触点的数量（$ j'\至0 $）的临界值，均和滑动的数量，均减少，随着$γ_0$的减少。对于由摩擦颗粒组成的悬浮液，我们还发现，随着$γ_0$的减少，关键（即〜剪切干扰）填充$ ϕ_c $会增加。在这两种情况下，摩擦和无摩擦，我们都发现，随着$γ_0$的降低，剪切干扰的流变响应从粘性转变为弹性响应，低于$ \ sim0.33。
Oscillatory shear has been widely used to study the rheological properties of suspensions under unsteady shear. Furthermore, recent works have shown that oscillatory flows can improve the flowability of dense suspensions. While most studies have been done under constant volume we here study oscillatory shear flows of a two-dimensional suspensions using a normal pressure-controlled set-up. To characterise the rheology, we introduce both a complex macroscopic friction coefficient $μ^{*}$, following the convention of the complex viscosity $η^{*}$, and a shear-rate averaged viscous number $J'$. The rheology and microstructure of dense suspensions are studied by systematically varying both the strain magnitude $γ_0$ and $J'$ using numerical simulations. We study both suspensions composed of frictional ($μ_p=0.4$) or frictionless ($μ_p=0$) particles and find that the critical values, as $J' \to 0$, of both the complex macroscopic friction and the number of contacts, both total and sliding, decrease with decreasing $γ_0$. For suspensions composed of frictional particles we also find that the critical (i.e.~the shear jamming) packing fraction $ϕ_c$ increase with decreasing $γ_0$. In both cases, frictional and frictionless, we find that the rheological response approaching the shear jamming turns from a viscous to an elastic response as $γ_0$ is lowered below $\sim0.33$.
