非布朗型磁流变液的表观屈服应力
On the Apparent Yield Stress in Non-Brownian Magnetorheological Fluids
摘要：
我们使用模拟来探测致密的二维磁流变液的流动特性。来自实验和模拟两者的先前结果报告剪切应力$σ$与应变率$\dot γ$成比例为$σ\sim \dot γ^{1-Δ}$，指数值在$2/3 <Δ\le 1$之间变化。然而，仍然不清楚系统的什么性质选择$Δ$的值，特别是在什么条件下系统显示屈服应力（$Δ= 1$）。为了解决这些问题，我们进行模拟的一个极简模型系统中，粒子通过长距离的磁偶极子力，有限范围的弹性排斥，和粘性阻尼相互作用。我们发现一个令人惊讶的依赖性的表观指数$Δ$的形式上的粘性力的法律。对于体积分数$ϕ$和无量纲梅森数（量化粘性和磁应力之间的竞争）的实验相关值，使用斯托克斯样阻力的模型显示$Δ\approx 0.75$，没有明显的屈服应力。当耗散发生在接触，但是，一个明确的屈服应力平台是明显的稳态流动曲线。在任一种情况下，朝向堵塞转变增加$ϕ$足以引起屈服应力。我们将这些定性不同的流动曲线在颗粒尺度上的聚类机制。对于类斯托克斯阻力，系统建立各向异性，链状集群的梅森数趋于零（消失的应变率和/或高场强）。相比之下，对于接触阻尼，由于非弹性碰撞，存在第二种聚集机制。
英文摘要：
We use simulations to probe the flow properties of dense two-dimensional magnetorheological fluids. Prior results from both experiments and simulations report that the shear stress $σ$ scales with strain rate $\dot γ$ as $σ\sim \dot γ^{1-Δ}$, with values of the exponent ranging between $2/3 <Δ\le 1$. However it remains unclear what properties of the system select the value of $Δ$, and in particular under what conditions the system displays a yield stress ($Δ= 1$). To address these questions, we perform simulations of a minimalistic model system in which particles interact via long ranged magnetic dipole forces, finite ranged elastic repulsion, and viscous damping. We find a surprising dependence of the apparent exponent $Δ$ on the form of the viscous force law. For experimentally relevant values of the volume fraction $ϕ$ and the dimensionless Mason number (which quantifies the competition between viscous and magnetic stresses), models using a Stokes-like drag force show $Δ\approx 0.75$ and no apparent yield stress. When dissipation occurs at the contact, however, a clear yield stress plateau is evident in the steady state flow curves. In either case, increasing $ϕ$ towards the jamming transition suffices to induce a yield stress. We relate these qualitatively distinct flow curves to clustering mechanisms at the particle scale. For Stokes-like drag, the system builds up anisotropic, chain-like clusters as the Mason number tends to zero (vanishing strain rate and/or high field strength). For contact damping, by contrast, there is a second clustering mechanism due to inelastic collisions.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
