Potisk Tilen, Svenšek Daniel, Pleiner Harald, Brand Helmut R
Department of Physics, University of Bayreuth, 95440 Bayreuth, Germany.
Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia.
J Chem Phys. 2019 May 7;150(17):174901. doi: 10.1063/1.5090337.
An effective macroscopic model of magnetorheological fluids in the viscoelastic regime is proposed. Under the application of an external magnetic field, columns of magnetizable particles are formed in these systems. The columns are responsible for solidlike properties, such as the existence of elastic shear modulus and yield stress, and are captured by the strain field, while magnetic properties are described by the magnetization. We investigate the interplay of these variables when static shear or normal pressure is imposed in the presence of the external magnetic field. By assuming a relaxing strain field, we calculate the flow curves, i.e., the shear stress as a function of the imposed shear rate, for different values of the applied magnetic field. Focusing on the small amplitude oscillatory shear, we study the complex shear modulus, i.e., the storage and the loss moduli, as a function of the frequency. We demonstrate that already such a minimal model is capable of furnishing many of the key physical features of these systems, such as yield stress, enhancement of the shear yield stress by pressure, threshold behavior in the spirit of the frequently employed Bingham law, and several features in the frequency dependence of storage and loss moduli.
提出了一种用于粘弹性状态下磁流变流体的有效宏观模型。在外部磁场作用下，这些系统中会形成可磁化颗粒柱。这些颗粒柱导致了诸如弹性剪切模量和屈服应力等类固体性质的存在，并被应变场捕获，而磁性则由磁化来描述。我们研究在存在外部磁场的情况下施加静态剪切或法向压力时这些变量之间的相互作用。通过假设一个松弛应变场，我们针对不同的外加磁场值计算了流动曲线，即剪切应力作为施加剪切速率的函数。聚焦于小振幅振荡剪切，我们研究了复剪切模量，即储能模量和损耗模量，作为频率的函数。我们证明，即使是这样一个极简模型也能够呈现这些系统的许多关键物理特性，例如屈服应力、压力对剪切屈服应力的增强作用、类似于常用宾汉定律的阈值行为，以及储能模量和损耗模量频率依赖性的若干特性。
