半固态流变学模型的研究进展

半固态金属(SSM)加工是金属成型的一项新技术。SSM加工以半固态金属浆料作原料。SSM浆料通常表现出两种独特的流变特性：假塑性和触变性。SSM各种加工方法都是在这两个特性的基础上发展起来的。所以，发展SSM加工方法要从掌握浆料的流变特性开始。总结比较了现有的流变学模型。     

半固态材料流变特性研究进展与分析

半固态材料流变特性研究是半固态金属加工技术研究的重要组成部分。本文着重介绍一些国内外半固态流变特性研究的概况和最新进展，包括：实验方法、研究类别、连续冷却研究、假塑性研究、触变性研究、高固相分数研究。     

半固态加工中的触变强度及其影响因素研究

结合半固态金属具有触变性的特点,提出触变强度是触变点对应的应力,阐述了触变强度的研究意义,并结合高固相率下半固态金属等温压缩真应力-应变曲线研究了外变量包括坯料的加热温度、应变速率、保温时间和内变量包括固相体积分数、晶粒尺寸、晶粒的球形度、结构参数、半固态材料的固相屈服强度、半固态材料的初始表观粘度等对触变强度的影响。     

半固态金属基复合材料的制备及流变性研究进展

简述了用半固态加工工艺制备金属基复合材料的主要方法及原理.讨论了制备过程中各工艺参数对材料制备的影响及后续的触变成形加工.综合评述了半固态金属基复合材料的流变性研究现状.     

碳黑—醇酸树脂体系的流变性与分散稳定性关系

通过沉降法和透射电镜直接表征了碳黑颜料－醇酸树脂分散体系的分散稳定性，同时测试了各分散体系的流变性、研究了流变性与分散稳定性的关系。结果表明，碳黑－醇酸树脂体系的分散稳定性愈好，抗絮凝性愈强，其流变性愈接近于牛顿行为；反之，分散体系的稳定性愈差，则其触变性愈显著，触变环愈大。     

现场混装乳化炸药基质的流变性研究

从流动性、黏弹性和触变性3方面研究了现场混装乳化炸药基质的流变性。从流动性曲线可知,在低速剪切区域,乳化基质呈现牛顿流体性质。剪切速率继续升高后,乳化基质呈现剪切变稀型非牛顿流体性质。触变性试验结果说明,乳化基质结构恢复能力和所受外力大小有关,外力越大,乳化基质的结构越难恢复。黏弹性曲线表明,应变升高后,乳化基质逐渐从弹性形变转变成黏性形变。此外,乳化基质流变性受分散相液滴尺寸的影响较大。液滴尺寸减小,黏度和储能模量升高,外力消除后,乳化基质的结构恢复能力提高。     

半固态浆料制备技术发展现状

半固态成形技术与传统成形技术相比,以其诸多的优点日益受到越来越多研究者的关注.在半固态成形技术的研究中,制备具有非枝晶组织的理想半固态浆料(坯料)是关键.将半固态浆料制备工艺分为两大类:液态金属半固态浆料制备和固态金属半固态坯料制备,并分别介绍了两类工艺中常用的几种工艺方法.电磁搅拌法和应变诱化激活法已有工业化应用;双螺旋搅拌法和半固态等温热处理法等比较有发展潜力;其他多种方法各有特点,可用于特定合金或者特定工作条件下的研究开发.     

增稠剂对乳液流变性的影响

实验测定了国产TH-01和TH-02增稠剂的性能,考察了不同增稠剂含量对国产BC-01和As-102乳液的流变性的影响。 用NXS-11型旋转粘度计的弹簧松弛技术测定了低剪切速率(γ<1.0秒~(-1))下的乳液流变数据,得出剪切速率和剪切应力之间服从幂律定律,从而得到k值和n值。并讨论了乳液的触变性和屈服值。     

铜合金半固态流变成形及制备技术研究进展

金属半固态成形已有近50年的发展历史,因其加工优势和市场价值备受关注,并形成了很多加工方法,其中半固态流变成形工艺效率高、成本低,具有较好的发展前景。由于铜合金熔点普遍较高,目前针对其进行的半固态工艺研究较少。简要综述了针对铜合金的半固态流变成形及制备技术的研究新进展,包括各新工艺的加工过程、最优工艺参数选择及工艺过程的机理等,分析了各工艺目前尚存在的问题和原因。阐述了半固态流变制备工艺模型及机理的新进展,并对其发展趋势进行了分析和展望,认为半固态流变成形技术未来的研究方向有半固态浆料制备新方法、新型半固态合金和半固态组织演变机制及其控制方法等。     

半固态方法可制备高度完整的铝铸件

半固态铸造是一种备选的成型工艺，可在传统的模铸机中制备高度完整的铸件。与传统工艺不同，半固态铸造是基于部分固化的具有非枝晶球形显微结构的铝或镁合金。综合这两种特征，半固态工艺的优点有：     

Rheology of fresh concrete: from measurements to predictions of casting processes

This paper tries to make a link between the measurements of the rheological properties of fresh concrete (yield stress and thixotropy) and casting processes. In the first part, methods allowing for the measurement of the yield stress of a given concrete without the use of a rheometer will be described. In a second part, a thixotropy model allowing for the prediction of the apparent yield stress of the material as a function of its flow history will be presented. Finally, in the last part, prediction methods of casting process will be presented. These methods can be considered as practical tools allowing for the prediction of formwork filling, pressure formwork or multilayer casting occurrence. Moreover, they contribute to bringing rheology from research and development into the field of practical applications. Dr Nicolas Roussel presented a lecture of this paper at the 2007 RILEM annual week in Ghent, Belgium, as he was awarded the 2007 Robert L’Hermite Medal in recognition of his work on rheology of concrete. The L’Hermite Award Committee for 2007 decided to recommend the prize to Dr Roussel in recognition of his extensive scientific work within rheology of concrete. In particular his physical analysis of concrete rheology and his ability to combine experimental and theoretical work are of high quality.     

Alkali-activated slag concrete: Fresh and hardened behaviour

The behaviour of fresh and hardened alkali-activated slag (AAS) and OPC concretes was compared and the effect of mixing time assessed. OPC and AAS concrete slump and rheological results proved to differ, particularly when the slag was activated with waterglass (WG). The nature of the alkaline activator was the key determinant in AAS concrete rheology. Bingham models afforded a good fit to all the OPC and AAS concretes. In OPC and NaOH-activated AAS concretes, longer mixing had an adverse effect on rheology while improving hardened performance only slightly. In WG-AAS concrete, longer mixing times, improved mechanical properties and also rheological behaviour was enhanced, in which those conditions were required to break down the microstructure. Longer mixing raised thixotropy in OPC and NaOH-activated AAS concretes, but lowered the value of this parameter in waterglass-activated slag concrete.     

Field-oriented test methods to evaluate structural build-up at rest of flowable mortar and concrete

Thixotropy of flowable mortar and concrete is an important property that affects stability and form pressure characteristics. The increase in thixotropy can reduce lateral pressure on formwork systems. On the other hand, low thixotropy or a continuous casting is required to eliminate the formation of weak interface between lifts in multilayer casting. Thixotropy can be assessed by determining the rate of structural build-up at rest, which necessitates the use of simple and robust test methods to be quantified. Five field-oriented test methods that can be used for the determination of structural build-up at rest of mortar and concrete are proposed in this paper in an attempt to select a reliable field-oriented test. This includes the inclined plane (IP), portable vane (PV), undisturbed slump spread (USS), cone penetration (CP), and K-slump test methods. The repeatability of these test methods was determined four times using two concrete-equivalent mortars and two self-consolidating concretes (SCC) of different thixotropy levels. The IP, PV, and USS tests showed relative error (RE) values of 0.5?C37?%. The CP test was successfully used to determine structural build-up of mortar; however, it was difficult to assess the thixotropy of concrete. The K-slump test exhibited a RE, less than 12?% for SCC mixtures with low thixotropy, but up to 76?% for highly thixotropic SCC. Good correlations were established among the various structural build-up indices determined from the proposed test methods and those determined by rheometric tests using various concrete.     

基于三参量流变模型的止水橡皮粘弹性研究

给出了用三参量流变模型研究止水橡胶粘弹性的基本表达式。结合某高水头闸门 止水材料的粘弹性试验,得到了所采用橡胶材料的流变参数,并指出了其蠕变变形和应力松弛变化的规律,为工程设计提供参考依据。     

Rheology of concrete: a study case based upon the use of the concrete equivalent mortar

A deeper and wider knowledge of the rheology of concrete could be obtained if a variety of absolute rheological parameters were measured. Although a valuable rheological classification can be induced from concrete rheometers, they do not give the same absolute values of the rheological parameters. Moreover, rheological tests with concrete require a large volume of material. The aim of this work is to use the concrete equivalent mortar (CEM) method (Schwartzentruber and Catherine, Mater Struct 33:475–482, 2000) to get concrete rheological information with an absolute rheometer. Additionally some graph tools that resume the results from several rheological tests are suggested for the design of concretes. CEM have been formulated to test concrete formulations with an absolute rheometer. Steady flow measurements of a CEM corresponding to a self-compacting concrete (SCC) clearly reveal characteristic non-linear viscoplastic behavior which it is not shown by conventional tests used to characterize concretes. The thixotropic behavior of a concrete is well-established using three different rheological tests that can be made with an absolute rheometer testing its corresponding CEM. These tests reveal aspects of the strength and kinetics of the micro-structure that are not observable when thixotropy of concrete is semiquantified with conventional methods. Only with a CEM is possible to make oscillatory shear tests. In this way the viscoelastic behavior of the concrete can be characterized. Results of practical interest are so obtained. For example, the necessity of vibration at rest application to the fresh concrete can be established from frequency sweep tests of CEM in the linear viscoelastic region. The correlation between rheological behaviors of a concrete and its corresponding CEM has been supported. Steady flow and thixotropy rheographs of CEM are suggested as tools for an easy and fast determination of adequate formulation for specific applications.     

Novel testing method for thixotropy of paste slurry with respect to influencing factors and rheological parameters

Paste slurry exhibits significant thixotropy, which has a significant influence on the slurry pipeline transportation resistance. This paper proposes a novel test method for the thixotropy of paste slurry, which can ensure that the slurry reaches flow equilibrium during the test. Accordingly, the influences of the solid mass concentration, cement-to-tailings ratio, and temperature on thixotropy were studied by employing a control variable method, and the influences of the above three factors on the stress overshoot and rheological parameters were evaluated. The results revealed that the solid mass concentration and temperature have significant influence on the thixotropy. Moreover, with an increase in the solid mass concentration, the time required for the slurry to reach flow equilibrium decreases. The cement content and temperature are proportional to the significance of the stress overshoot, and the change in dynamic yield stress can be considered an indicator for the effective quantification of thixotropy. In the continuous shearing cycles, the maximum apparent viscosity at the start of shearing significantly decreases on the time axis. The solid mass concentration has a significant influence on the minimum apparent viscosity in the slurry flow process, whereas the cement-to-tailings ratio and temperature have no significant influences.     

纳米纤维素对两性蠕虫胶束线性黏弹性的影响

对两性蠕虫胶束（Z-WLM）溶液添加不同类型纳米纤维素（NCs）后的耐温性能进行了研究,并通过线性流变学方法分析了不同浓度的NCs对Z-WLM的动态黏弹性、触变性、蠕变性等流变行为的影响。研究结果表明,质量分数为4wt%的芥酸酰胺丙基二甲基甜菜碱表面活性剂溶液可形成蠕虫胶束（WLM）结构,具有剪切稀释性、黏弹性、蠕变性及良好的触变回复性等特性。与其它类型NCs相比,长径比大、羧基含量高的NCs对WLM溶液拥有更好的增黏作用,同时可增加体系的松弛时间、弹性模量,延长其剪切黏度及动态模量触变回复时间,改善其蠕变回复性和耐温性,适用于70~100℃的中高温油藏增产作业使用。随着NCs添加量的增加,复合体系的黏弹性和蠕变回复性增强,触变回复性减弱。      

Comparison of the flow properties of aqueous suspension corticosteroid nasal sprays under differing sampling conditions

Many aqueous suspension corticosteroid nasal sprays become less viscous when shaken and sprayed, then return to a more viscous state after application. This time-dependent, reversible loss of viscosity under shear (e.g., shaking or spraying) can be quantified in the rheological property of thixotropy. The flow properties of 5 corticosteroid nasal sprays were measured over a range of shear rates. The formulations tested included Nasonex, Vancenase AQ, Nasacort AQ, Rhinocort Aqua, and Flonase. The yield stress values, as well as an estimate of thixotropy, were compared by using three different sampling techniques, including one that simulated patient use (shaking for 30 sec, spraying, and immediately transferring the sample to the rheometer). The rheological properties of all products indicated that when initially shaken and dispensed, they flowed more freely, followed by recovery of viscosity that would likely inhibit the suspensions from flowing out of the nasal cavity. Under all three tested conditions, Nasonex exhibited the highest yield stress, the largest apparent initial and final viscosities, and the highest apparent thixotropy. The study protocol that simulated patient-use conditions produced the following rank order of measured thixotropy: Nasonex > Flonase > Vancenase AQ > Rhinocort Aqua > Nasacort AQ. The thixotropy of Nasonex was 3.4 to 21.4 times greater and the final viscosity was 3.2 to 17.4 times greater than the values of the other tested products.     

纳米CaCO3对水泥-石灰石粉浆体流变作用

试验采用Rheolab QC型旋转黏度计测试了掺纳米CaCO₃的水泥-石灰石粉浆体的流变曲线,应用Herschel-Bulkley流变模型对其剪切应力-速度（τ-γ）曲线进行拟合,得到浆体的动态屈服应力、稠度系数和流变指数,并用触变环面积表征浆体的触变性。结果表明：随石灰石粉掺量的增加,水泥-石灰石粉浆体的动态屈服应力逐渐减小,稠度系数增大,触变性先增大后减小;纳米CaCO₃未改变水泥-石灰石粉浆体的流变类型都呈现出剪切稀化行为;随纳米CaCO₃掺量的增加,水泥-石灰石粉浆体动态屈服应力和稠度逐渐增大,触变性减小,纳米CaCO₃使水泥-石灰石粉浆体流变性能变差,但使其稳定性增强。     

磁流变液触变性评价指标研究

实验研究了可用于磁流变液触变性的评价指标。研究表明,基于表观粘度与剪切速率曲线得到的触变破解指数,测试简便且重复性好,可作为磁流变液触变性能的评价指标。触变环的测试数据具有良好的稳定性,含有丰富的材料性能信息,也可作为磁流变液触变性的评价指标,且较低的剪切速率以及较低的持续时间,易于得到较为显著的触变环。