絮凝污泥悬浮液流变性质研究

研究了某污泥悬浮体系经絮凝处理后的流变行为.絮凝剂为800万分子量的非离子型聚丙烯酰胺,流变参数测定仪器为美国Brookfield公司的DVIII 型流变仪.实验结果表明:悬浮体系的表观粘度随着污泥浓度的增加而增大,两者关系符合爱因斯坦多项式;絮凝污泥属于非牛顿流体,具有剪切变稀的特性,剪切应力与剪切速率的关系可用Herschel-Bulk模型描述;随体系固体浓度的增大,屈服应力τ0及稠度系数k增大,流动指数n下降,并且结合絮凝与流变学理论简要分析了实验结果的机理.     

中密度钨-镍-粉末注射成形喂料的流变性能与流动本构模型

研究了中密度系列钨-镍-铁(烧结后密度分别为10,14,17 g·cm-3)粉末注射成形喂料的流变行为,分析了在相同粘结剂和粉末装载量的条件下,剪切速率、温度以及钨镍成分配比对喂料流变性能的影响.结果表明:钨-镍-铁喂料属于非牛顿型流体,遵从假塑性熔体的流动规律,具有较高的熔体粘度;其表观粘度随剪切速率的增大、温度的升高而减小;非牛顿指数随温度的升高而增大;钨在合金中所占比重越大,喂料对剪切速率的变化及温度的变化越敏感;利用非线性回归技术拟合流变参数,得到了喂料的流动本构模型.     

中密度钨-镍-铁粉末注射成形喂料的流变性能与流动本构模型

研究了中密度系列钨-镍-铁(烧结后密度分别为10,14,17 g.cm-3)粉末注射成形喂料的流变行为,分析了在相同粘结剂和粉末装载量的条件下,剪切速率、温度以及钨镍成分配比对喂料流变性能的影响。结果表明:钨-镍-铁喂料属于非牛顿型流体,遵从假塑性熔体的流动规律,具有较高的熔体粘度;其表观粘度随剪切速率的增大、温度的升高而减小;非牛顿指数随温度的升高而增大;钨在合金中所占比重越大,喂料对剪切速率的变化及温度的变化越敏感;利用非线性回归技术拟合流变参数,得到了喂料的流动本构模型。     

液固温区A356合金瞬态流变行为的研究

采用自行研制的流变装置进行瞬态流变试验,研究了切应变速率突变对液固温区不同初生α相形态A356合金瞬态流变行为的影响规律。初生α相形态是以切应变速率为141.8s-1的等温剪切获得的不同程度的退化枝晶。研究表明,等温剪切过程将使半固态合金的初生α相逐渐退化,表现为表观粘度逐渐降低直至达到平衡态。对试验结果进行回归分析,得出表观粘度与时间的瞬态流变经验方程,以及方程参数与半固态合金初生α相形态和切应变速率之间的关系。由研究结果可知,随着初生α相形态由发达枝晶向球状晶变化,半固态合金剪切稀释或伪塑性越显著,同时对时间具有更加强烈的依从性,从而具有更明显的触变性。     

剪切历史对长庆含蜡原油流变性的影响研究

对不同剪切历史作用后的长庆含蜡原油流变性能进行实验研究.通过改变剪切时间和剪切速率,模拟了管流现场的剪切历史作用,通过测量不同剪切历史作用后油样的凝点和粘度变化,研究了剪切历史对长庆含蜡原油流变性的影响规律,并针对剪切作用对含蜡原油流变性影响的作用机制进行了分析.结果表明:低温低速长时间的剪切作用对含蜡原油流变性能影响较大,低速剪切会增大含蜡原油的凝点和粘度,长时间的高速剪切作用会优化含蜡原油的流变性能.     

高粘度煤泥加压旋转流变仪的标定与应用

高粘度煤泥流变特性是影响其高压管道输送阻力的一个重要因素．故研制加压旋转流变仪测量高粘度煤泥不同压力时的流变特性。标定加压旋转流变仪,用于测试压力对流变性的影响。使用加压旋转流变仪测试浓度75％煤泥的剪切应力和剪切速率．绘制了煤泥不同压力时的流变曲线和表观粘度曲线,通过分析确定了煤泥常压下是宾汉型流体,加压下为屈服假塑性流体。     

聚氨酯基磁流变胶的剪切流变特性

制备了不同质量分数(50%,70%,80%)羰基铁粉的聚氨酯基磁流变胶(MRG),研究具有较宽剪切应力范围的MRG在不同磁感应强度、剪切速率、应变幅下的静态和动态剪切流变特性,并基于试验结果对Herschel-Bulkley本构模型参数进行了识别。结果表明:随着磁感应强度的增强,含质量分数80%羰基铁粉MRG的剪切应力范围最宽、磁流变效应最明显;含质量分数80%羰基铁粉MRG的屈服剪切应力随磁感应强度增强而增大,且不同磁感应强度下的动力学黏度都随着剪切速率的增大而减小;该MRG是一种具有屈服剪切应力以及剪切稀化特性的非牛顿流体,其流变特性满足Herschel-Bulkley剪切稀化模型;储能模量和损耗模量受剪切应变幅及磁感应强度的影响较大,而对频率的依赖性微弱;磁流变效应及线性黏弹性临界应变幅都随磁感应强度增强而增大;相比于剪切速率及应变幅,磁感应强度对法向应力的影响更显著。     

基于ER阻尼的WEDM电极丝恒张力微机控制

电流变液是一种可控智能阻尼介质,其表观粘度和剪切屈服应力随外加电场发生快速变化。设计了一种以ER阻尼器为执行元件的恒张力微机控制系统,系统响应快,较好地解决了电火花线切割加工过程中的张力测量和控制精度问题,实现了电极丝的恒张力控制。     

聚吡咯在几种连续介质中的电流变效应

研究了聚吡咯在液体石蜡、硅油和蓖麻油中的电流变效应。结果表明：随着电场强度、聚吡咯浓度的增加，电流变液的漏电流增大，而随着剪切速率的减小，漏电流却增大。由蓖麻油和聚吡咯组成的电流变液的电流变效应最好。     

添加碳纳米管的液体石蜡油流变特性的研究

为分析添加碳纳米管的润滑油流变和润滑特性，在液体石蜡油中加入碳纳米管作为添加剂，形成的润滑介质在HAAKE—RV20旋转流变仪上进行了流变试验。实验结果表明，添加了碳纳米管的液体石蜡的初始粘度增大，并随着剪切速率的提高而下降，表现出明显的剪切稀化效应。为解释实验结果，推导了二阶传递函数模型表示含碳纳米管石蜡油的非牛顿流体本构关系，并分析了非牛顿流体的动态特性对润滑介质特性的影响。     

Calculated load capacity of non-newtonian lubricants in finite width journal bearings

Starting from the most general type of fluid flow equation connecting cubic shear stress to rate of shear for non-Newtonian lubricants, a modified form of Reynolds' equation was derived for steady finite width journal bearings. The finite difference technique with successive over relaxation was used incorporating Reynolds' boundary conditions for pressure to obtain the pressure distribution and hence the load capacity and the attitude angle. It is shown that the flatter pressure profile and higher load capacity at low eccentricity ratios have practical advantages. The apparent viscosity loss at higher rates of shear decreases the load capacity at higher eccentricity ratios but it is expected that the flatter viscosity temperature slope of the polymer thickened non-Newtonian lubricants will compensate for their apparent viscosity decrease.     

A new capillary viscometer for small samples of whole blood

A new capillary viscometer is described in which a column of blood is discharged under a constant pressure, producing a variety of shear stresses during a single test. Measurement of the viscosity of Newtonian sucrose solutions showed good agreement between the viscosity determined from the new system and the expected values. The viscosity of whole blood was measured in a cone-and-plate viscometer at a wide range of shear rates and characterized using a power law model; good agreement was obtained between the capillary and rotational results at low and medium shear rates. High shear rate results could also be obtained by increasing the driving pressure. The new viscometer proved to be simple to use, utilized a small test volume and produced reliable results.     

润滑脂流变性对滚动轴承振动性能的影响

采用表观粘度仪和振动仪研究了润滑脂的流变性对轴承振动性能的影响.研究发现,润滑脂在一定剪切速度下的表观粘度偏低对轴承振动性能有利,但润滑脂的表观粘度非常小时,在加工精度较差的中大型轴承上振动噪声性能反而不够理想;润滑脂的流变性能对中小型轴承振动噪声的影响有决定性作用,对微小型轴承的振动性能影响不明显,这符合摩擦学行为系统依赖性的规律.     

New Method of Measuring Permanent Viscosity Loss of Polymer-Containing Lubricants

An ultrahigh shear rate viscometer (USV) was used to measure the viscosity of polymer solutions. It was found that some polymer solutions in base oil, including those used as engine oil viscosity modifiers, show permanent viscosity loss when subjected to very high shear rates above 10⁶ s^?1. The USV was modified to automatically carry out a series of viscosity measurements on the same test lubricant sample. This enabled the accumulation of permanent viscosity loss to be measured over successive strain cycles.

As expected, permanent viscosity loss increased with both strain rate and molecular weight. When carried out at 5 × 10⁶ s^?1 and 100°C, the test was more severe than the Kurt Orbahn test because samples of lubricants subjected to the latter underwent further shear thinning in the USV.

The USV test appears to be a rapid and convenient way to quantify the permanent viscosity loss of polymer-containing lubricants for engine use, and a protocol to assess permanent viscosity loss (PVL) and permanent shear stability index (PSSI) based on viscosity measurements at 10⁶ s^?1 before and after shear thinning is outlined.

The study also shows that it is important to take into account possible permanent viscosity loss when measuring the viscosity of polymer solutions in very high shear rate viscometers such as the USV. This can be done by minimizing the amount of shear to which the lubricant is subjected or by taking successive measurements and subtracting the permanent viscosity loss taking place in each of the first few strain rate cycles.     

聚合物熔体微尺度剪切黏度测量方法与黏度模型

研究微尺度效应下聚合物熔体黏度时,发现不同入口修正方法获得的剪切黏度随特征尺寸变化的规律不同,这对于聚合物微成型理论和技术尤为重要。采用直径分别为1 000μm、500μm、350μm的毛细管口模,在相同试验条件下分别用零口模法和Bagley法两种入口修正方法,研究高密度聚乙烯(High density polyethylene,HDPE)、短链支化的聚丙烯(Polypropylene,PP)、聚甲基丙烯酸甲脂(Polymethylmethacrylate,PMMA)和聚苯乙烯(Polystyrene,PS)四种材料的剪切黏度变化规律。结果发现,两种方法获得的PMMA和PS黏度随口模直径变化的规律相反,指出传统入口修正方法在测量微尺度黏度时存在局限。基于入口收敛流动特征,提出一种考虑微尺度效应下压力影响的测量方法,并用该方法给出四种材料剪切黏度随口模直径变化的真实规律。试验剪切速度范围内,四种材料剪切黏度均随口模直径的减小而减小,平均变化幅度为9.9%～38.3%,并从分子结构角度揭示四种材料黏度变化程度不同的机理。基于黏度变化规律,采用唯象性方法建立适用于宏—微观尺度下的黏度模型。试验结果表明该模型的理论预测结果与试验结果平均误差小于3.7%,验证了模型的正确性和有效性。     

半流体脂的流变性与润滑机理研究

半流体脂由于其独特的流变性，兼具有润滑油与脂的优点而获得越来越广泛的应用。本文利用毛细管粘度计和ＲＶ２型流变仪研究了半流体脂的弹流润滑机理。     

温度引起的流体非牛顿特性研究∗

为了研究温度效应对润滑失效的影响,通过求解合理简化后的能量方程,推导出了考虑温度效应的非牛顿流体本构方程。通过实验测得黏温系数,代入工况条件后绘制函数图像。对图像以及所得数据进行分析发现:接触区的出口处为润滑过程的最危险点,随着剪应变率的增大,润滑液首先表现出牛顿流体的性质,然后慢慢出现剪切稀化现象;在剪应变率增大到一定程度时,剪应力会达到极限;此后若剪应变率继续增加,剪应力不再随之上升,将出现润滑失效现象。     

Analysis of frictional phenomena in friction welding of mild steel

A dynamical analysis of the “equilibrium phase” of friction welding is presented. The fundamental idea is that the observed phenomena are controlled by the behaviour of a viscous layer of plasticised metal at the rubbing surfaces. This layer is postulated to obey a constitutive equation relating shear stress to rate of strain which is similar to the well-known “Bingham plastic” model. Formulae are thus obtained which predict the external driving torque, as well as the thickness and temperature distribution of the plasticised layer. A comparison is made between the theoretical results and a number of experiments which have been carried out on mild steel tubular specimens, over a range of conditions. Good agreement is found in all cases. Preliminary results are presented for the apparent viscosity of plasticised mild steel.     

Thermo‐elasto‐hydrodynamic lubrication model for journal bearing including shear rate‐dependent viscosity

The simulation of the non‐stationary response of the journal bearings used in combustion engines plays a significant role in the bearing design process. Diverse simulation models contain various oil viscosity definitions taking pressure and temperature into consideration. However, viscosity dependence on the shear rate is often neglected. Within this paper, a bearing simulation model including the shear rate‐dependent viscosity is described. The modified Cross equation was used to describe shear rate influence on viscosity. Numerical modelling of the main crankshaft bearing of a modern four‐cylinder gasoline engine was performed. Selected calculation results were discussed and conclusions drawn. The modelling and calculation were carried out using the AVL software EXCITE (AVL LIST GmbH, Advanced Simulation Technology, Hans‐List‐Platz 1, Graz, Austria 8020). Copyright © 2007 John Wiley & Sons, Ltd.     

Calculated Performance of Greases in Journal Bearings

A digital computer analysis has been made of the effects of non-Newtonianism on the performance of greases in finite width journal bearings. As anticipated, t he extreme nonlinearity of the shear rate-shear stress relation exhibited by greases makes their deviations from “normal” behavior very marked. Among the effects noted are (1) apparent “anisotropic viscosities,” i.e., viscosities in the side leakage direction as much as 30 times as high as those in the direction of motion, (2) reduced side leakage, (3) flatter pressure profiles, (4) reduced sensitivity of load and friction to speed changes relative to Newtonian lubricants, and (5) the occurrence of “cores” of plug flow. Theoretically interesting is the fact that the apparent axial viscosity approaches the true viscosity while the circumferential viscosity approaches the slope of the flow curve. Many of the conclusions obtained here, especially the advantages of greases at low speeds, are confirmed in practice.