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%.

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.

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 α-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. Whith 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 yied stress is higher than that at pH=4. The addition of both PVA and PEG was found to prevent the filter cake from cracking.

Analysis of complete plasticity assumption for solid circular shaft under pure torsion and calculation of shear stress

The distribution of shear stress on the cross-section of plastic metal solid circular shaft under pure torsion yielding,the applicability of complete plastic model assumption and the shear stress formula were researched.Based on the shear stress formula of circular shaft under pure torsion in elastic stage,the formula of torque in elastic stage and the definition of yield,it is obtained that the yielding stage of plastic metal shaft under pure torsion is only a surface phenomenon of torque-torsion angle relationship,and the distribution of shear stress is essentially different from that of tensile stress when yielding under uniaxial tension.The pure torsion platform-torsion angle and the shape of torque-torsion angle curve cannot change the distribution of shear stress on the shaft cross-section.The distribution of shear stress is still linear with the maximum shear stress τs.The complete plasticity model assumption is not in accordance with the actual situation of shaft under torsion.The experimental strength data of nine plastic metals are consistent with the calculated results of the new limiting strain energy strength theory(LSEST).The traditional yield stress formula for plastic shaft under torsion is reasonable.The shear stress formula based on the plane assumption in material mechanics is applicable for all loaded stages of torsion shaft.

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。

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。

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.

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。

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).

pH Valaue Effects in Shear Rheology of Concentrated Alumina Suspensions

1 INTRODUCTIONThe suspensions employed in ceramic processing arehighly concentrated.These suspensions are normallyknown as slip or slurry in materials science and engi-neering.It is of great interest that concentrated sus-pension exhibit many of the phenomena of very dilutecolloidal suspensions.This is probably because boththe suspension systems have charged particles,so thatthe principles of colloid chemistry can be applied forthem.

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

双孔微剪切法测定材料的局部强度

工程上进行焊接接头强度设计或承载能力评定时,需要测定焊接接头各区域的局部强度.文章提出一种双孔微剪切局部强度试验测定方法.在被测材料的小区域两侧开2个小孔,剪切压头从其中一孔对被测区域加载直到破坏,根据加载过程中的载荷位移曲线,确定材料的强度.实验说明,该方法具有很好的重复精度.通过对管线钢、紫铜和6063铝合金三种材料的标准拉伸和双孔微剪切的对比试验,发现拉伸屈服强度是屈服剪应力的2.01倍,抗拉强度是最大剪应力的1.46倍.最后测定了焊接接头局部强度,其分布趋势与硬度值基本相似.

基于链化分析的磁流变液剪切屈服应力模型

基于磁性颗粒在磁场作用下的链化分析和统计分析方法,建立了磁流变液的宏观屈服剪应力的分析模型.模型考虑了磁感应强度、颗粒尺寸、体积分数、剪应变率以及饱和磁化强度等因素,能描述不同剪切应变率下剪切应力的变化及在高应变率下可能出现的剪切稀化效应.分析了不同因素对剪切屈服应力的影响,讨论了提高磁流变液剪切屈服应力的途径.分析表明,该模型的计算结果能较好地描述有关实验现象,并可用于高性能磁流变液的设计分析.

基于宾汉姆体的高浓度尾砂浆剪切变稀规律研究

高浓度尾砂浆的活化搅拌一直是矿山充填技术研究的重要方向,采用高速搅拌活化充填料浆是破坏充填料浆"团块"的有效办法,能够明显改善充填料浆的流变特性,提高其可输送性。高速搅拌过程的实质是对充填料浆进行快速剪切,不同的搅拌能对应不同的剪切速率,料浆的物化性质也相应地存在差异。为研究这种差异的规律并寻找高浓度尾砂浆的最佳活化能,针对某铜矿充填用尾砂,配制了浓度为70%的尾砂浆,采用新诺AM300S-H实验室搅拌机对尾矿浆开展了多种转速的搅拌实验,并采用Broofield R/SCCT型流变仪分别测试其流变参数,通过Bingham模型分析了剪切变稀特性。研究结果表明:高浓度尾矿浆的黏度(η_b)和屈服应力(τ_0)随搅拌速率(n)的增加而减小,表现出明显的剪切变稀特性,当转速达到400 r/min之后,尾砂浆的屈服应力不再明显减小,有趋于稳定的特性;在转速为120~1 000 r/min的范围内,其黏度与剪切转速之间的关系可用η_b=0.3n^(-0.1)表示。

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。

旋转式磁流变测试仪的设计与研究

由于磁流变液的应用前景广阔,而市场上磁流变液性能测试系统相对短缺,为了更好地促进磁流变液的工程应用,有必要研究磁流变液的性能测试仪。通过理论计算和实验验证的方法,设计了一种磁流变旋转式测试仪,用实测的办法验证了磁场理论计算的正确性。测试表明,当电流为1.6A时磁场达到0.5582T,MRF4的剪切应力达到70.12KPa,当电流为1.4A,磁场为0.5483T,剪切屈服强度51.6KPa。

胶凝大庆原油不同加载时间下的屈服特性

为得到胶凝大庆原油的屈服过程与加载时间之间的关系,利用Haake RS-150控制应力流变仪通过恒剪切应力、剪切应力匀速增加和阶跃式增加3种不同的加载方式对其屈服过程进行了实验。研究发现:胶凝大庆原油的屈服过程与加载时间存在密切关系,屈服是变形随时间积累的结果;加载过程中各水平的应力作用时间延长,所得到的胶凝原油屈服应力下降,但屈服所需的时间延长,即应力值与作用时间相互弥补,在一定范围内小应力长加载时间和大应力短加载时间都能造成胶凝原油屈服;对剪切应力阶跃式加载而言,屈服应力随每阶段持续作用时间(单阶作用时间)的增加呈指数规律下降,屈服时间随单阶作用时间增加在双对数坐标中呈线性增加。