Effects of shear flow and viscosity difference on phase separation

We discuss some salient features recently found in phase-separating fluids under shear. They are highly elongated, bicontinuous domain structures (string phase), hysteresis in the droplet distribution in the off-critical case. existence of the spinodal due to suppression of droplet formation in shear. and critical rheology. We also examine the condition of bicontinuity and the effective viscosity when the two phases have different viscosities.Paper presented at the Twelfth Symposium on Thennophysical Properties, June 19–24, 1994 Boulder Colorado U.S.A.     

Giesekus流体在环形流道中脉动挤出的应力分析

以Giesekus粘弹模型为基础，推导出了轴向振动力场作用下聚合物熔体在环形流场中的应力计算公式，并结合实际的模型参数作了分析。结果表明：在环形流道中，流体的应力是半径和时间的函数，剪切应力与时间成余弦关系。内半流场的剪切应力随半径变化速率要明显大于外半流场的剪切应力变化速率，内环壁面处的剪切应力也要大于外环壁面处的剪切应力，Tiw／Tcw随k值变小而变大。     

磁流变液的流变学性质研究

用球形羧基铁颗粒、硅油和油酸制备了磁流变液（ＭＲＦ），该ＭＲＦ不加外磁场是就呈现非牛顿性，ＭＦＲ的剪切应力τ随剪切率γ的变化关系为一曲线，其表观粒度ηａｐ随剪切速度的增大而减小，在外磁场作用作用，ＭＲＦ的ηａｐ迅速增大两个数量级，ＭＲＦ呈现一定的屈服应力τｙ＝９４．７Ｐａ，当τ〉τｙ后，ＭＲＦ的流变特性满足Ｂｉｎｇｈａｍ模型。     

磁流变液及其阻尼器的制备与性能研究

研究了一种新型MR液和MR阻尼器;用振动样品磁强计测试了MPS-MRF-25羰基铁粉的磁性能;用磁流变仪测试了MR液的表观粘度和磁致剪切应力;用静置沉降法分析了MR液的抗沉降稳定性;用电液伺服材料性能试验机测试了MR阻尼器的性能.结果表明MPS-MRF-25羰基铁粉具有优良的磁性能;以其制备的MR液具有较好的抗沉降稳定性和温度稳定性;MR阻尼器在2A电流下可以达到15kN的阻尼力.     

磁流体在交变磁场中的热效应研究

制备了平均粒径分别为4、6 和8nm 的Fe3O4 粒子,将其分散在不同的介质中,在63kHz、7kA/m的交变磁场中研究其热效应。实验结果显示,粒径较大的Fe3O4 粒子具有较高的产热比功率(SAR),Fe3O4 粒子经过表面处理后SAR显著增加,而且SAR随表面活性剂不同而不同,还显示SAR与磁场强度的平方成正比。     

交变电场影响生理盐水冰结构的介电方法研究

以生理盐水为试验样品,研究不同条件下生理盐水冻结后形成的冰结构.实验结果显示,交变电场作用使冰的介电常数显著增加.提出复合冰结构模型,根据电介质物理理论,研究分析交变电场对复合冰结构的影响.分析结果表明,在交变电场作用下,复合冰结构中含盐冰成分增加,而纯水冰成分减少.     

电流变体智能材料在交变电场下的透光性能研究

电流变体作为智能材料作动器的一种,在外加电场的作用下,其材料性能会发生显著的变化。本文主要研究了二氧化硅／淀粉复合颗粒电流变体在交变电场作用下的透光性能的变化。对不同浓度的流体、不同外加电场强度,不同外加电场频率以及不同电极间距几种情况下电流以变体的透光性均进行了测试。     

电场磁场对电流变液体减振器性能影响的研究

由于电流变液和磁流变液具有良好的可控性能和力学性能而在工程上具有广阔的应用前景.本文将其用于环形间隙通道外置的双缸电流变液体减振器.同时,对电流变液减振器在同时外加电场和垂直磁场作用下阻尼力的变化进行了理论研究和台架实验研究.结果表明,在外加电场和垂直磁场作用下,电流变效应得到加强,改善了减振器的示功特性.     

Effect of thickness on buckling of perfect cross-ply rings under external pressure

Effect of thickness on the buckling of a perfect thick plane strain cross-ply ring (very long cylindrical shell) is investigated. A linearized version of a fully nonlinear finite element analysis, that employs a cylindrically curved 16-node layer-element, and is based on the assumption of layer-wise linear displacements distribution through thickness (LLDT), is utilized for computation of hydrostatic buckling pressure of the afore-mentioned cross-ply ring. Numerical results pertaining to the effect of thickness (interlaminar shear/normal deformation) on the hydrostatic buckling pressure of cross-ply rings and comparison with their classical lamination theory (CLT) counterparts are also presented.     

采用信号处理方法研究粘性液体剪弹性动力学特性

通过改善实验流体与基片的边界连接,发现粘性液体在几十μm的厚度下,以低速率、小应变剪切即使远离其相变温度,也可以观察到其具有剪弹性动力学特性。为了进一步揭示这种特性,采集实验中的应力-应变信号,并应用离散傅立叶变换（DFT）对信号进行分析,根据流变学理论从应力与应变的相位差角度证明液体在一定条件下存在剪弹性特性。     

速度、压力场对铝液侵蚀模具的影响

为了探明压铸生产过程中熔融铝合金速度、压力场对模具侵蚀过程的影响及其作用机理,本文设计动态侵蚀试验,通过计算流体动力学仿真软件计算旋转试样圆周区域速度场和压力场分布状态,观察试样表面的宏观形貌并利用SEM、EDS作元素微量分析。结果显示:试样前端与尾端区域速度最大,前端与远端之间压力场最大;流体压力场对试样侵蚀的影响属压应力作用,促进原子间的扩散,加快金属间化合物生成的速度,加剧试样表面的侵蚀程度;流体速度场对试样侵蚀的影响属切应力作用,导致生成并附着于试样表面的金属化合物层剥离,造成深坑状的腐蚀形貌。     

Multiple shear step approach to determine the rotational viscosity of asphalt emulsions and its correlation with water content of original and diluted emulsions

Viscosity determination of thixotropic emulsions with good repeatability has always been a major challenge. Currently, Saybolt Furol viscometer (SFV) is used to determine the viscosity of the emulsion, but the main drawback of the SFV is that it cannot simulate the behaviour of emulsion under different shear rate. Rotational viscometer (RV) can measure viscosity at different shear rates. Due to the thixotropic behaviour of the emulsions, getting repeatable results by following the hot binder specification is a problematic task. In this study, a new multiple shear step approach is used to determine the viscosity of the emulsified asphalt using RV. Three low viscous (SS-1, SS-1H and SS-1L) and two high viscous (CRS-2 and CRS-2P) emulsions were used in this study. Shear stress is gradually stepped up to different levels after certain time interval to determine the viscosity. In this manner, emulsion undergoes a known shear state and each reading is preceded by a certain repeatable shear history. It was observed that with the progression of time and simultaneous increase in shear rate, the viscosity results are much more stable and repeatable with less than 5% coefficient of variance. The final specifications proposed are 220–730 and 5–90 cP at 50 rpm and 30 °C for high and low viscous emulsions, respectively, which are based on 98% probability. Viscosity measured by this approach also showed strong correlation with water content (R² > 0.94). The correlation between viscosity and water content is even stronger after dilution. With different dilution water content, viscosity of CRS-2 and CRS-2P exhibited R² values of 0.97 and 0.98, respectively.     

Spinodal decomposition and nucleation in the presence of flow

Spinodal decomposition and nucleation of critical fluids are discussed in the presence of laminar shear and turbulence on the basis of recent experiments. In such situations we can realize stationary emulsion-like domain structures due to dynamical balance between thermodynamic instability and shear-induced deformations. In the spinodal decomposition case, unique is the strong shear regime in which the shear exceeds the average relaxation rate of the order parameter. In the nucleation case shear can enhance aggregation of droplets, thus speeding up the growth. But if the shear exceeds a relatively small critical value, even critical droplets can be broken, then leading to complete suppression of the droplet formation. We also predict a considerable increase of the effective viscosity and a large non-Newtonian effect due to domains in the course of spinodal decomposition.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

钛酸钙系电流变液在直流电场下静态剪切的应力响应

研究了直流电场下钛酸钙系电流变液在静态剪切模式下的力学响应,得到了材料在静态剪切模式下的应力应变关系,讨论了材料温度、电压和剪切应变对应力的影响,以理论推导和实验数据拟合的方法得出了剪切应力与剪切应变、温度以及电场强度等参数的半经验数学关系式.理论值对比实验结果表明,剪切应力表达式与实验结果符合较好,可以用于预测材料在静态剪切模式下的剪切应变,温度和电场强度对剪切应力的影响.     

电场对Al-Mn-Mg合金的微结构和织构形成的影响

利用透射电子显微镜观察(TEM)和X射线衍射技术(ODFs分析),研究了电场对Al-Mn-Mg合金的回复和再结晶组织演变、再结晶织构的形成和发展的影响.结果表明,电场对再结晶的影响其强度有一个门槛值(3～4 kV/cm),低于此值电场对该合金的再结晶没有明显的影响.强度为4 kV/cm的电场对再结晶形核的影响较大,可抑制Al-Mn-Mg合金的回复和再结晶,促进再结晶立方织构的形成.其主要原因是电场降低了各取向的形变储能,推迟了再结晶进程,抑制储存能小的取向晶核的形成和长大,促进储存能大的S取向晶粒向立方织构择优生长.     

振动挤出过程中毛细管内聚合物熔体的剪切应力分析

不依赖现有的任何本构关系，并考虑惯性项的影响，建立了平行叠加振动条件下毛细管内聚合物熔体剪切应力的计算公式；实验测量一定振动频率和振幅下毛细管瞬时入口压力、瞬时体积流量、以及体积流量与入口压力波形的相位差，通过上述公式即可求得振动力场下毛细管内聚合物熔体的剪切应力分布。     

Rheological properties of boehmite sols during ageing at room temperature (30 ±1°C) under closed condition

Boehmite sols were obtained by peptizing boehmite precipitates with glacial acetic acid. The sols were aged at room temperature (30 ±1°C) under closed condition. Rheological properties of the sols were studied at different ageing times. The sol characteristics were interpreted by measuring their viscosity, areas of hysteresis of the flow curves and yield stress (τ_y). Viscosity and the area of hysteresis of the flow curves increased with increasing ageing time of the sols. A sharp change of yield stress was observed during the ageing period from 15 to 36 days. The change in viscous to elastic nature and the appearance of gel point of the sol was observed by studying their oscillatory flow behaviour, i.e. by measuring loss modulus(G″), elastic modulus (G′), and loss tangent (tan δ) of the sols. Gel point of boehmite sol was found at 36 days of ageing under closed condition at room temperature (30 ±1°C).     

平面应变模具尺寸差对金属流变及其力能的影响

采用MARC/Superform有限元软件对平面应变压缩过程进行了二维有限元分析,分析了上下模具尺寸不相等时,对金属流变规律及其力能参数的影响.同时应用滑移线场理论对端部的滑移线场进行了分析,分析了金属的流动情况,进一步验证了有限元模拟结果的可靠性.研究结果显示:模具尺寸相等时,金属流动呈现对称分布;当上下两个模具尺寸不等时,金属流动呈现非对称分布,有剪切变形产生.而且随着模具尺寸差的增大,其交叉剪切变形越严重,总压力也增大,平均压力相对降低,这与异步轧制过程类似.所研究结果为异步轧制过程提供了一种新的物理模拟方法.     

电场作用下水分子转向极化和离子扰动对生物溶液相变过程的影响

从水分子偶极转向极化和离子迁移运动两个方面分析了电场对生物溶液相变过程的影响.电场作用下产生的水分子偶极转向极化,使定向在电场方向上的水分子具有最稳定的状态,并且水分子沿电场方向上的麦克斯韦-波尔兹曼能量分布函数具有最大值,电场效应具有诱发冰核形成和抑制冰晶生长的作用.电场作用下产生的离子迁移运动,扰乱了水分子排列结构,改变了水分子的运动状态,造成了溶液内部电荷密度变化,对冰晶生长具有强烈的抑制作用.     

Effects of fiber misalignment and transverse shear modulus on localization and shear crippling instability in thick imperfect cross-ply rings under external pressure

The effect of transverse shear modulus on the compressive response of a thick plane strain cross-ply ring (very long cylindrical shell) weakened by the presence of a modal imperfection is investigated. The present study is primarily motivated to obtain the hitherto unavailable results pertaining to the effect of reduced transverse shear modulus, , of a lamina weakened by the presence of randomly distributed fiber misalignments. A simple expression for the reduced transverse shear modulus, , of a layer material is derived in terms of the average fiber misalignment angle. A fully nonlinear finite element analysis, that employs a cylindrically curved 16-node layer-element and is based on the assumption of layer-wise linear displacement distribution through thickness (LLDT), is utilized in the analysis of the afore-mentioned cross-ply ring. The interaction of a micro-structural defect in the form of initial fiber misalignments with its macro-structural counterpart represented by a modal imperfection is a key to understanding this meso-structural level phenomenon. Hitherto unavailable numerical results pertaining to the influence of this effect on the localization of buckling patterns and the ensuing shear crippling instability are also presented.