YIELD STRESSES IN ELECTRORHEOLOGICAL FLUIDS
YIELD STRESSES IN ELECTRORHEOLOGICAL FLUIDS
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DOI：
10.1122/1.550343
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发表时间：
1992-01-01
影响因子：
3.3
通讯作者：
BRADY, JF
中科院分区：
文献类型：
--
作者：
BONNECAZE, RT;BRADY, JF
我们从微观结构模型中描述和确定电流变（ER）流体中的静态和动态（宾厄姆）屈服应力。该模型将这两个屈服应力与由悬浮电容矩阵确定的静电能联系起来，悬浮电容矩阵是我们之前为电流变流体的动态模拟而开发的。静态屈服应力由非线性弹性应变能理论确定，该理论适用于各种体积分数和颗粒-流体介电常数比的电流变流体。静态屈服应力随介电常数比增大而增大，当介电常数比小于等于4时，静态屈服应力在40 vol %颗粒处达到最大值。从悬架的电容值出发，计算了电流变流体的零频率双折射，并证明了它遵循非线性应力-光学规律。正如我们在之前的模拟中观察到的那样，动态屈服应力在大电场强度下主导着电流变流体的流变学。同时，悬架的静电能经历了反复缓慢的增加，然后迅速下降或跳跃。动态屈服应力与模拟中观察到的这些能量跳跃之间的联系来源于剪切ER悬架的总能量平衡。在梅森数Ma较低时，粘性力与静电力之比，动态屈服应力等于平均能量跳变与其频率的乘积，并通过动态仿真成功地验证了该理论。利用这一理论，建立了一个简单的模型来预测体积分数和颗粒-流体介电常数比对动态屈服应力的影响。我们发现动态屈服应力和静态屈服应力一样，随着介电常数比的增加而增加，并且在颗粒体积分数为40%时存在最大值。有了对动态屈服应力来源的了解，我们就能够预测用内质流体获得的最大屈服应力。
We describe and determine the static and dynamic (Bingham) yield stresses in an electrorheological (ER) fluid from a microstructural model. The model relates both these yield stresses to the electrostatic energy determined from the suspension capacitance matrix, which we developed previously for the dynamic simulation of an ER fluid. The static yield stress is determined from nonlinear elasticity strain-energy theory applied to an ER fluid for a variety of volume fractions and particle-to-fluid dielectric constant ratios. The static yield stress increases with the dielectric constant ratio and exhibits a maximum at 40 vol % particles for dielectric constant ratios of 4 or less. From the capacitance of the suspension we also compute the zero-frequency birefringence of the ER fluid and show that it follows a nonlinear stress-optical rule. The dynamic yield stress, as we have observed in our previous simulations, dominates the rheology of the ER fluid at large electric field strengths. At the same time the electrostatic energy of the suspension undergoes repeated slow increases, followed by rapid decreases or jumps. The connection between the dynamic yield stress and these energy jumps observed in the simulations is derived from a total energy balance of a sheared ER suspension. At low Mason number, Ma, the ratio of viscous forces to electrostatic forces, the dynamic yield stress is found to be equal to the product of the average energy jump and its frequency, and the theory is successfully tested using our dynamic simulation. Using this theory, a simple model is developed that predicts the effects of volume fraction and particle-to-fluid dielectric constant ratio on the dynamic yield stress. We find that the dynamic yield stress, like the static yield stress, increases with dielectric constant ratio and there is a maximum for a volume fraction of 40% particles as is indeed observed experimentally. With this understanding of the origin of the dynamic yield stress, we are able to predict the maximum yield stress obtainable with an ER fluid.