磁流变液微结构的实验观测

磁流变液(MRF)的力学性能与其微结构密切相关,而其微结构的形成与演化受多种因素的影响。研究了静磁场和剪切作用下磁流变液微结构的形成与演化。在静磁场作用下,分析了颗粒体积分数和磁感应强度对其微结构的影响;在剪切作用下,观测了微结构的动态演化过程。实验结果表明,在相同磁感应强度下,随着颗粒体积分数的增加,通链数目逐渐增多,孤立链减少,且由相互独立的单链转变为相互聚集的束链,在相同颗粒体积分数下,随着磁感应强度的增加,颗粒链的间距增大,链的聚合度明显提高;在剪切过程中,成功地捕捉到了磁流变液颗粒链从形成→拉伸→断裂→重组的动态演化过程,当该过程达到动态平衡时,为磁流变液提供了稳定的抵抗宏观剪切的能力。     

磁流变液的流变特性分析和实验验证

本研究制备了羰基铁粉体积分数为10%的硅油基磁流变液,使用Physica MCR 301流变仪测试其流变性能,用Bingham模型和Casson模型对磁流变液的流变性能进行拟合计算。实验表明,Bingham模型和Casson模型均可较好地描述磁流变液的流变行为,在磁场作用下,随着剪切速率增加,剪切应力增大并趋于稳定,表观粘度显著减小,磁流变液存在剪切稀化现象。通过对数拟合的方法,得出磁流变液剪切应力和磁场的关系,剪切速率恒定时,随着磁场增大,磁流变液剪切应力显著增加。     

圆筒式磁流变离合器的设计分析

磁流变离合器是通过磁流变液的剪切应力传递转矩的器件.本文建立了圆筒式磁流变离合器的几何设计方法,得到了磁流变液传递的转矩和两圆筒间能产生磁流变效应的最小间隙的设计计算公式,为离合器的几何设计奠定了理论基础.研究结果表明:转矩可由外加磁场连续控制;选择磁饱和时高屈服应力和零磁场时低粘度的磁流变液材料,能使设计的离合器的尺寸小而紧凑.     

磁场作用下磁流变液剪切性能的实验分析

本文研究了磁流变液的力学性能,制备了羰基铁粉体积分数为20%的硅油基磁流变液,观察了磁流变液在磁场作用下的微观变化,测试了磁流变液的剪切性能。实验表明,无磁场作用下,磁流变液为牛顿流体;在磁场作用下,随着剪切速率的增加,剪切应力趋于稳定,表观粘度呈现指数式下降,磁流变液具有剪切稀化效应,符合广义Bingham模型。磁流变液剪切应力和外加电流的依赖关系为:在电流较小时,剪切应力表现为指数增长,指数值约为1.5;随着外加电流的增大,剪切应力表现为线性增长,最终达到稳定值。     

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。     

考虑磁性颗粒不均匀分布的磁流变液修正微观力学模型及试验验证

为了研究磁性颗粒在磁场作用下的不均匀分布对磁流变液力学性能的影响,通过卡方分布来模拟磁性颗粒的间距分布,对现有的磁流变液微观力学模型进行修正,并通过磁流变阻尼器的力学性能试验验证了模型的有效性。在磁流变液双链微观力学模型的基础上,修正相邻磁性颗粒的间距完全相等且不随磁感应强度而变化的假设,采用卡方分布来表征磁性颗粒间距的不均匀分布,并引入分布参数来描述磁性颗粒间距随磁感应强度的变化关系,推导了考虑磁性颗粒不均匀分布的磁流变液修正微观力学模型;基于修正的微观力学模型,分析了分布参数对磁流变液剪切屈服应力的影响;将该文提出的磁流变液修正微观力学模型带入到磁流变阻尼器的准静态模型中,可以得到不同电流下的阻尼器最大出力,并与磁流变阻尼器力学性能试验数据进行对比来验证所提模型的有效性。结果表明,考虑了磁性颗粒不均匀分布的磁流变液修正微观力学模型可以更加精确地预测磁流变液在不同磁感应强度下的剪切屈服应力,尤其是在低磁感应强度情况下可以改善现有微观力学模型放大了磁流变液剪切屈服应力的缺点。     

磁流变液在圆筒间的粘塑性流动

磁流变液具有粘性和粘塑性流体特性.基于Navier-Stokes方程,分析了外加磁场对在两圆筒间隙间的磁流变液粘塑性流动的影响,得到了速度和流量表达式,为圆筒式磁流变器件的设计提供了理论依据.研究结果表明:速度沿磁场方向呈抛物线和直线分布;流量可由外加磁场连续调控.     

集料对透水沥青混合料空隙率的影响

为了保证透水沥青混合料具有良好的排水性能,采用体积法研究了粗、细集料对透水沥青混合料空隙率的影响程度和变化规律。研究结果表明,当2.36mm筛孔通过质量百分率由12%逐渐增加到21%时,透水沥青混合料空隙率逐渐减小,在12%时达到最大值17.9%;当4.75mm筛孔通过质量百分率由12%逐渐增加到24%时,透水沥青混合料空隙率先增大后减小,说明4.75mm筛孔通过质量百分率存在最佳值,为15%,此时空隙率达到最大值19.7%。2.36mm、4.75mm筛孔通过质量百分率对透水沥青混合料空隙率有着重要的影响。矿料间隙率和有效沥青饱和度也可以用来表征透水沥青混合料的体积特征。     

磁流变胶泥材料的磁控力学行为实验研究

采用主要成分为高粘度线性聚硅氧烷的弹性胶泥为基体,制备了羰基铁粉质量分数为20%,40%和60%的磁流变胶泥。对磁流变胶泥的流变学特性和动态力学特性进行测试,描述了磁流变胶泥的本构关系并识别其参数,分析了磁场、铁粉含量、剪切应变以及剪切频率对粘弹性能的影响。结果表明,磁流变胶泥的本构关系能用Herschel-Bulkley模型进行描述;剪切应力、刚度的磁场可控范围宽(铁粉质量分数为60%的磁流变胶泥剪切应力调节范围16~128kPa,储能模量可调范围0.52~3.28 MPa);随铁粉含量和磁场的增加,剪切应力增大、弹性增加而粘性减小;不同磁场下磁流变胶泥从线性粘弹性区向非线性粘弹性区转变的临界应变值不同,且磁场增大可拓宽线性粘弹性区的范围;在线性粘弹性区磁流变胶泥对0~80Hz频率无依赖性。     

温度对磁流变液材料及传力性能的影响

针对不同温度下磁流变液的性能差异巨大,造成高温环境条件下磁流变液流变效应下降、剪切力变化不可控甚至传动装置传动失效等问题,分析了温度对磁流变液及其剪切应力的影响,在此基础上建立了磁流变传动装置的有限元模型对传动装置工作时的温度场进行分析。研究结果表明,温度对磁流变液的黏度有较大影响,进而影响磁流变液的流变特性和屈服应力;温度对磁流变液的力学性能影响明显,特别是在温度高于100℃后,材料在磁场下的成链受到显著影响,造成流变效应下降、剪切力变化不可控等问题;磁流变液工作时磁性颗粒间的滑差会造成磁流变液温度的显著升高。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Analysis of marine hydrobiont lipid extracts as possible cryoprotective agents

We studied a combined effect of the cryoprotectants both of lipid and carbohydrate origin at the presence of DMSO or without it on cell viability and the RNA synthesis in the embryonic mollusc and echinoderm cell cultures obtained at different developmental stages. Cryoprotective properties of exogenous lipids correlated with their thermotropic behavior. Lipid extracts from marine hydrobiontes, which thermal transitions are characterized by relatively small part of calorimetric thermogram area lying at temperatures above 0 °C (6–18%), were found to possess a considerable cryoprotective activity. The results are discussed in relation to the prediction of the cryoprotective activity of lipid extracts for marine animal cells. In addition, it was found that marine invertebrate cells can be cryopreserved without DMSO at the presence of trehalose and lipid extracts of some marine hydrobiontes.     

Low-Temperature Properties of Silver

Pure silver is used extensively in the preparation of high-temperature superconductor wires, tapes, films, and other configurations in which the silver not only shields the superconducting material from the surrounding materials, but also provides a degree of flexibility and strain relief, as well as stabilization and low-resistance electrical contact. Silver is relatively expensive, but at this stage of superconductor development, its unique combination of properties seems to offer the only reasonable means of achieving usable lengths of conductor. In this role, the low-temperature physical (electrical, thermal, magnetic, optical) and mechanical properties of the silver all become important. Here we present a collection of properties data extracted from the cryogenic literature and, to the extent possible, selected for reliability.