A New Modified Conductivity Model for Prediction of Shear Yield Stress of Electrorheological Fluids Based on Face-center Square Structure

A new modified conductivity model was established to predict the shear yield stress of electrorheological fluids (ERF). By using a cell equivalent method, the present model can deal with the face-center square structure of ERF. Combining the scheme of the classical conductivity model for the single-chain structure, a new formula for the prediction of the shear yield stress of ERF was set up. The influences of the separation distance of the particles, the volume fraction of the particles and the applied electric field on the shear yield stress were investigated.

Effects of PVA and PEG on pH Dependent Shear Yield Stress of Concentrated Alumina Suspensions

The pH dependence of the extrapolated shear yield stress for Alcoa A16 a-Al2O3 suspensions at the powder volume fraction of 0.27 with and without addition of both polyvinyl alcohol (PVA) and polyethylene glycol (PEG) each at fixed 0.18% of the powder mass was studied. With the polymer added, the full deflocculation of the suspension shifts from about pH=4 to around pH=1.5, at which the minimum value of shear yield stress is higher than that at pH=4. The addition of both PVA and PEG was found to prevent the filter cake from cracking.

Rheological properties and concentration evolution of thickened tailings under the coupling effect of compression and shear

Cemented paste backfill(CPB)is a key technology for green mining in metal mines,in which tailings thickening comprises the primary link of CPB technology.However,difficult flocculation and substandard concentrations of thickened tailings often occur.The rheological properties and concentration evolution in the thickened tailings remain unclear.Moreover,traditional indoor thickening experiments have yet to quantitatively characterize their rheological properties.An experiment of flocculation condition optimization based on the Box-Behnken design(BBD)was performed in the study,and the two response values were investigated:concentration and the mean weighted chord length(MWCL)of flocs.Thus,optimal flocculation conditions were obtained.In addition,the rheological properties and concentration evolution of different flocculant dosages and ultrafine tailing contents under shear,compression,and compression-shear coupling experimental conditions were tested and compared.The results show that the shear yield stress under compression and compression-shear coupling increases with the growth of compressive yield stress,while the shear yield stress increases slightly under shear.The order of shear yield stress from low to high under different thickening conditions is shear,compression,and compression-shear coupling.Under compression and compression-shear coupling,the concentration first rapidly increases with the growth of compressive yield stress and then slowly increases,while concentration increases slightly under shear.The order of concentration from low to high under different thickening conditions is shear,compression,and compression-shear coupling.Finally,the evolution mechanism of the flocs and drainage channels during the thickening of the thickened tailings under different experimental conditions was revealed.

Three-Dimensional Analysis of Rolling by Twin Shear Stress Yield Criterion

Using the twin shear stress yield criterion, the surface integral of the co-line vectors, and the integration depending on upper limit, Kobayashi＇s three-dimensional velocity field of rolling was analyzed and an analytical expression of rolling torque and single force was obtained. Through redoing the same experiment of rolling pure lead as Sims, the calculated results by the above expression were compared with those of Kobayashi and Sims formulae. The results show that the twin shear stress yield criterion is available for rolling analysis and the calculated results by the new formula are a little higher than those by Kobayashi and Sims ones if the reduction ratio is less than 30%.

盾构壁后注浆窜浆模型试验及发生条件研究

全断面围岩管片壁后注浆因向开挖面方向的窜浆现象会引起盾尾空隙注浆不饱满,管片上浮、错台及开裂,螺机喷涌等事故常有发生,已经引起广泛重视。通过设计自制壁后注浆液窜浆模型装置进行试验,分析浆液性质、缝隙厚度、注浆压力差对是否发生窜浆及窜浆量的影响,并探讨了不发生窜浆的临界条件。结果表明:(1)浆液压力与窜浆距离呈线性衰减,当浆液稠度较低时,窜浆量与缝隙厚度、浆液稠度呈近似线性正相关、与浆液的剪切屈服应力呈近似线性负相关,窜浆距离与注浆压力差呈近似线性正相关;当浆液稠度增大时,以上关系将逐渐转化为非线性关系;(2)通过极差分析表明浆液的窜浆量受盾壳与岩层间缝隙厚度影响最大,注浆压力与开挖面压力差影响其次,最后是浆液本身的性质;(3)建立了窜浆临界分析模型和计算公式,得到了窜浆发生条件和判别方法,可用于指导稳定围岩地层中盾构掘进时浆液的配制。

流变学参数表征湿喷混凝土工作性研究进展

为提高工作性对湿喷混凝土施工性能(可输送性、可喷性)的指导作用,归纳了现有各种技术规范的工作性要求,回顾了流变特性与可喷性相关性研究进展,探讨了流变性能时变机制,总结了时变模型发展现状。结果表明,坍落度无法协调可输送性与可喷性工作性需求矛盾,流变学参数应用效果优于坍落度;屈服剪切应力增加,一次喷射厚度变大,回弹率减小;塑性黏度降低,管道输送压力减小,可输送性变好,但屈服剪切应力、塑性黏度与密实度的相关性尚需深入研究;主流的流变性能时变模型为指数、对数、线性、幂函数等经验公式,应加强有物理意义的模型推导;时变预测模型缺乏有效验证手段,应重点研发速凝体系下湿喷混凝土流变性能的原位评估方法。

不同级配组成对泥沙流变特性影响实验研究

针对江苏沿海条子泥区域泥沙,运用控制剪切速率实验方法,通过改变样品中的粉沙质量占比,系统探究了泥沙的级配对其剪切应力和黏度的影响规律,并使用剪切速率扫描法和间接法分别计算泥沙样品静态和动态屈服应力。结果表明:所有组次泥沙样品均表现出两次明显的屈服行为,其流变特性以两个屈服行为为界,划分为3个阶段;泥沙样品中粉沙含量对其流变特性起着关键性作用,粉沙含量增大,样品剪切应力和黏度均发生相应减小,其中粉沙含量在35%~55%区间内变化梯度较大,此区间可能存在泥沙粒间主导作用力的转变;最后依托剪切速率扫描法测得的实验数据分析,得到了不同粉沙含量下泥沙的静态屈服应力和动态屈服应力的经验公式。

石墨添加剂对磁流变脂流变特性的影响

为了研究石墨添加剂对磁流变脂流变特性的影响,采用润滑脂为基体,制备了石墨粉末质量分数为0%,2%,5%,8%,10%的石墨磁流变脂(graphite magnetorheological grease,GMRG).使用安东帕流变仪测量了5种材料在稳态剪切模式和振荡剪切模式下的流变特性,并对石墨添加剂质量分数对磁流变脂屈服应力和黏弹性的影响进行了研究.结果表明,对比未添加石墨的磁流变脂,石墨质量分数分别为2%,5%,8%和10%的磁流变脂可以在加载电流为3 A时获得更高的屈服应力,并且屈服应力分别提升了40.49%,54.12%,81.48%和147.48%.此外,石墨添加剂质量分数越大,石墨磁流变脂的黏弹性特征就越明显,但获得的相对磁流变效应越小.研究还发现石墨质量分数的变化对石墨磁流变脂的线性黏弹区间影响不大.

含水率对黄土高原地区几种主要类型土壤流变特性的影响

[目的]研究含水率对土壤浆体流变特性的影响机理,为黄土高原地区泥浆体流动规律的认识和泥石流防治提供科学依据。[方法]以黄土高原地区4种主要类型土壤为研究对象,通过流变振荡剪切测试,探究含水率对土壤流变特性的影响。[结果](1)[土娄]土、褐土和黑垆土的储能模量、损耗模量、剪切应力随含水率的增加(40%~80%)均呈减小趋势,剪切应力分别从229.85,193.38,96.46 Pa减小到2.25,2.65,2.32 Pa;在含水率较大(>50%)的条件下,黄绵土表现出强应变过冲现象。(2)4种土壤浆体的储能模量随剪切应变的增加出现两个平台区,表现出两步屈服现象;随着含水率的增加,浆体出现两步屈服向一步屈服的转变。第一步屈服与初始网络结构的破坏有关,第二步屈服表明浆体结构被完全破坏。(3)当土壤含水率≤50%,土壤细颗粒可通过形成絮凝体增加絮凝程度从而提高土壤浆体流动点剪切应力;当含水率>50%时,土壤中的粗颗粒通过增加颗粒间摩擦力提高流动点剪切应力,此时黄绵土流动点剪切应力大于其他土壤。[结论]土壤流变特性不仅与其自身性质有关,而且受土壤含水率的重要影响;细颗粒含量较大的土壤,在高含水率条件下其浆体更易发生流动。

pH Value Effects in Shear Rheology of Concentrated Alumina Suspensions

The influence of pH on the rheological properties of concentrated alumina suspensions was investigated. At various pH values, the alumina exhibited pseudoplastic, near Bingham flow behaviors. The fully-deflocculated suspensions exhibited Newtonian flow behaviors, while the fully-flocculated suspensions demonstrated very high viscosity and shear yield stress.

流变调节剂在二元喷雾产品中的影响

选择了化妆品中常用的5种流变调节剂(卡波姆,丙烯酰二甲基牛磺酸铵/VP共聚物,聚丙烯酸酯交联聚合物-6,黄原胶和纤维素),分别配制含不同质量分数聚合物的水溶液和乳液体系。采用流变仪及马尔文喷雾粒度分析仪研究流变与喷雾行为。利用激光粒度仪测试各流变剂在水中形成的微凝胶粒径分布,并跟踪了乳液体系的稳定性。分析了流变行为及喷雾效果与流变调节剂在水溶液中的微观结构的关系。结果发现,黄原胶因其分子量较大,激光粒度仪测试其水溶液颗粒相对较大,虽然具有较好的剪切变稀性能,但其法向应力较高,不能提供良好的喷雾性能。卡波姆等其他4种聚合物,微凝胶颗粒较小,卡波姆含量较高时,因微凝胶颗粒致密而相互作用,可提供相对较高的黏度与弹性模量,但不利于喷雾,而聚丙烯酸酯交联聚合物-6因其适中的弹性模量,屈服应力和较低的法向应力,可作为辅助流变调节剂帮助乳液体系稳定,同时可以提供优良的喷雾效果。

高温铅铋轴流泵叶轮冲磨蚀特性研究

为研究铅铋轴流泵叶轮冲磨蚀特性,基于液态铅铋的冲磨蚀破坏机理分析,利用边界层理论建立冲磨蚀数学模型,采用SST k-ω湍流模型对0.8Q_(d)、1.0Q_(d)和1.2Q_(d)三种方案下泵内流动进行数值计算,获得了叶片冲磨蚀分布及壁面流速、流态、壁面熵产率与冲磨蚀的影响关系。结果表明:高冲磨蚀区域主要分布在叶片进口边靠近泵壳一侧;随铅铋泵入口流量增加和壁面流态紊乱加剧,叶片受冲磨蚀影响增大;当液态铅铋的最大流速不高于10m/s时,叶片受冲磨蚀影响较小,而最大流速高于10m/s时,叶片表面冲磨蚀急剧加重;叶片表面高冲磨蚀区域是高壁面熵产率主要分布区域,且液态铅铋的冲磨蚀行为与壁面熵产率呈正相关关系。

Investigation of the short-term stress distribution in stopes and drifts backfilled with cemented paste backfill

Cemented paste backfill(CPB) is largely used in underground mines worldwide.A key issue associated with application of CPB is to estimate the stresses in backfilled stopes and on barricades.Recent numerical and experimental results show that arching effect is absent shortly after the placement of CPB in stopes.However,stress decreases in barricade drift with increasing distance between the measurement points and drawpoint have also been observed,demonstrating arching effect shortly after the pouring of CPB.To explain these paradoxes,CPB is considered as Bingham fluid having a yield shear stress.Three dimensional analytical solutions are proposed to evaluate the short-term total stresses in backfilled stopes and on barricades,accounting for the CPB's yield shear stress-induced arching effect.Stress diminution due to such arching effect in the backfilled stopes and on barricades is indeed obtained.But the reduction becomes insignificant using typical yield shear stress and stope geometry.More analyses indicate that the typical yield shear stress values do not fully correspond to field conditions where the yield shear stress would increase exponentially due to apparent consolidation(loss of water by drainage,a phenomenon similar to the desiccation of overly saturated fine-grained materials).

GENERALIZED TWIN SHEAR STRESS YIELD CRITERION AND ITS GENERALIZATION

Ⅰ. INTRODUCTION The yield criterion or' materials under combined stresses is the important foundation for the research of constitutive law of materials, and widely used in the mechanics of solids, the strength of structures and the elasto-plastic analysis of structures. The three present

磁流变液颗粒成链过程的理论和实验研究

通过计算机模拟及实验研究了磁流变液颗粒在渐变磁场作用下的成链过程。首先从理论上建立了磁流变液成链过程的物理模型,采用蒙特卡罗方法模拟了其在渐变磁场作用下成链的详细过程。其次,采用光学显微镜观察了磁流变液在渐变磁场作用下的成链过程。数值模拟和实验结果表明,在平行磁场中,当外部磁场为零时,磁流变液的磁性颗粒处于随机分布状态。随着磁场强度的增加,磁性颗粒产生磁团聚形成链状絮凝体,进而由二连体或三连体发展到多连体,甚至网状及柱状结构;在倾斜磁场中,磁流变液中的聚合链也同时旋转,磁性颗粒沿着磁场方向从小链逐渐增大到大链,最后全部沿着磁场方向呈链状或柱状排列。研究结果对优化磁流变液材料的配置和设计高性能磁流变液装置具有重要意义。

磁流变液剪切屈服应力的数值计算

利用Maxwell应力张量 ,考虑颗粒的磁化饱和过程和非线性磁化过程 ,使用AN SYS软件三维有限元单元建立了基本力学模型 ,计算结果和实验取得了良好的一致 .并就颗粒的体积浓度、磁化饱和强度等对磁流变液性能的影响进行了计算和比较 .还构建了体心立方结构模型 ,初步计算了这种模型下磁流变液的剪切屈服应力 .

磁流变抛光液的研究

介绍了磁流变抛光的原理和特点,并由此提出了适于抛光的磁流变液的评价标准,根据这一标准选取了磁流变液的各组分,配制出了标准的光学抛光用磁流变抛光液。通过自行研制的磁流变仪测得该磁流变液在磁场为600mT,剪切率为110rad/s时的剪切屈服应力达到70kPa。用所配磁流变液对K9玻璃进行抛光实验,试验结果表明,磁流变抛光的材料最大去除率为0.4μm/min。

铅芯橡胶支座的非线性动态分析力学参数试验研究

通过对不同结构构造的铅芯橡胶支座进行水平动态力学试验, 系统研究了铅芯橡胶支座动态力学性能与其结构构造及外加动载之间的关系。研究结果表明:铅芯橡胶支座动态力学性能(特征强度、水平方向耗能、初始刚度、屈服后刚度及硬化比)主要由其本身的几何构造及组成材料决定,且在往复加、卸载循环过程中具有较好的稳定性。对试验数据进行数学统计分析,建立了铅芯橡胶支座各水平动态力学参数与其几何构造及外加荷载特性之间的一系列回归关系式。从而为铅芯橡胶支座的设计提供参考依据,为应用铅芯橡胶支座的结构进行非线性动态分析时,确定其动力分析参数提供可供参考的计算方法。

磁流变液剪切屈服应力的数值分析

为了改善单链模型的准确性,从颗粒间的磁相互作用能出发,建立了磁流变液多链计算模型.考虑链内颗粒和相邻链中颗粒的影响,利用磁能密度的变化,得到了磁致剪切应力应变关系,由剪切应力应变曲线的最大值来确定磁流变液的剪切屈服应力.对于链状结构,研究了链间距与链内相邻颗粒距离之比对磁流变液剪切屈服应力的影响;对于柱状结构,通过确定柱的大小及相邻柱的间距,构建了BCT结构计算模型,对含柱状结构的磁流变液的剪切屈服应力进行了分析.计算结果表明,当比值较大时,多链模型与单链模型趋于一致;比值较小时单链模型的误差不能忽略.传统的单链模型高估了磁流变液的剪切屈服应力,铁磁颗粒体积比浓度较小时,链状结构有比柱状结构更高的剪切屈服应力;而当颗粒体积比浓度较大时,柱状结构优于链状结构.

粗粒级膏体充填材料静动态抗离析性能表征

为表征粗粒级膏体充填材料的抗离析性能，基于固液两相流体力学及非牛顿流体力学，对粗颗粒的静动态受力进行分析，构建膏体充填料浆静动态抗离析力学模型。综合考虑浆体屈服应力、粗颗粒粒级分配和固液密度，提出抗离析性能表征模型，即离析判定值M。为检测该模型，以料浆浓度、粗颗粒最大粒径、尾碎比为三因素，进行9组正交实验，并对实验结果进行拟合分析。研究结果表明：离析判定值 M 的预测结果与实际结果一致，其中，M的最大值Mmax和M的平均值Mavg的拟合复相关参数均达到0.9以上，模型具有可靠性。合理选取粗颗粒粒径计算标准，即可实现对粗粒级膏体料浆抗离析性能的准确预测。建议离析判定值Mavg为1.0-2.5，离析判定值Mmax为1.0-1.2。