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。     

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。     

硅基磁流变粘弹性流体制备方法与流变学特性研究

针对磁流变液的静置沉降和磁流变弹性体控制范围小的问题,以六甲基二硅氧烷和聚二苯基硅氧烷的反应物作为磁流变材料的载体,加入特殊的添加剂,采用球磨分散方法,研制出了4种不同组分磁流变粘弹性流体(MRVF)样品。采用奥地利安东帕高级旋转流变仪(MCR-301)对上述样品进行了流变学性能测试。实验表明在剪切率为200s-1,磁感应强度为0～0.9T条件下,剪切应力的调节范围为5～120kPa;根据剪切应力与剪切率的关系曲线,采用高斯函数描述其本构模型,并运用最小二乘法辨识其模型参数;在25～80℃温度范围内测试了磁流变粘弹性流体的温度衰减特性,其剪切应力衰减不超过10%;经3个月静置观察,磁流变粘弹性流体的沉降率低于4%。     

基于弹性胶泥的新型高性能可压缩磁流变液

使用基于高粘度(≥200 Pa·s)线性聚硅氧烷的弹性胶泥作为磁流变液的载体液,研制了一类主要用于重型设备减振的新型磁流变材料——磁流变弹性胶泥。合成了三种粘度的弹性胶泥,并制备了相应的磁流变弹性胶泥样品。用傅立叶变换红外光谱技术对弹性胶泥样品进行了检测,并研究了磁流变弹性胶泥的可压缩性。结果表明,所研制的磁流变弹性胶泥在30 d观测期内无明显沉降,表现出优异的磁流变效应(磁通密度为0.54 T时基于800 Pa·s,60%质量分数样品的剪切屈服应力约为120 k Pa,零场时的15.4倍,甚至在高磁场下超过了流变化的初测试极限)。在流变曲线上首次发现一种特殊的"V形槽磁流变效应",从弹性胶泥特殊螺旋高分子链结构角度分析了其机理及其对磁流变弹性胶泥性能的影响。     

磁流变液的特性研究

对以金属铁颗粒为主体的磁流变液的一般特性进行了研究。详细研究了材料的颗粒大小、形状、比例以及温度等对磁流变液特性的影响。研究了流体的屈服应力与磁场关系,剪切应力与磁场以及剪切速率的关系。实验发现,磁流变液出现磁饱和现象不仅与材料特性有关,而且与配比比例有关;剪切应力不仅与材料的颗粒大小有关,还与材料的制备工艺有关。     

基于中空钴微米颗粒的磁流变液性能研究

采用水热法制备钴微米颗粒,通过X射线衍射仪、扫描电镜和振动样品磁强计对颗粒的相结构、形貌及磁性能进行表征。结果表明,颗粒为密排六方结构的单质钴,粒径3~5μm,内部呈中空结构,饱和磁化强度为161A·m2/kg。以中空钴微米颗粒为悬浮相,以硅油为基液,制备颗粒体积分数为12%的磁流变液。测试结果表明,基于中空钴微米颗粒的磁流变液的磁致剪切屈服强度在250kA/m磁场下达到37kPa,剪切应力的时间稳定性、长期静置的沉降稳定性等均优于同体积浓度的羰基铁粉磁流变液。     

Fe-Cr-Mo合金颗粒对磁流变弹性体损耗因子的影响

为改善磁流变弹性体(MRE)的阻尼性能,使用Fe-Cr-Mo合金颗粒(通过电火花方法制备得到)与硅橡胶混合制备得到了MRE样品.利用DHVTC振动测试系统测试了MRE在0~500 m T磁场范围内的动态剪切性能(激振频率为5 Hz,应变振幅为1.90%).重点研究了Fe-Cr-Mo颗粒对MRE的损耗因子的影响.结果表明,Fe-Cr-Mo合金颗粒含量达到70%时,MRE的零场损耗因子具有最大值0.24.此外,当磁场强度达到500 m T时,MRE(颗粒含量为60%)的损耗因子增加了13%.增加MRE中Fe-Cr-Mo合金颗粒含量,或者增大外磁场都会导致MRE损耗因子的提高.     

磁流变胶泥磁致流变学行为微观动力学模型研究

针对磁流变胶泥材料在外加磁场作用下悬浮相内磁相互作用机理和材料设计参数不确定的问题,根据磁流变材料微观偶极子理论,建立铁磁颗粒在磁场中的平板单链模型,结合链与磁场夹角之间满足指数分布的规律,得出了磁流变胶泥材料剪切屈服应力的理论表达式;根据磁流变胶泥材料的实验数据,对理论分析模型进行了修正,使模型能更好地预测不同影响因素下的剪切屈服应力值;对磁流变胶泥剪切屈服应力与铁磁颗粒、质量分数、基体粘度等因素进行分析,为高性能磁流变胶泥材料的设计、制备提供理论指导。     

稠化剂含量对磁流变脂流变行为的影响

稠化剂含量是决定磁流变脂骨架结构强度的重要因素,对磁流变脂的实际应用具有较大的影响。实验制备了羰基铁粉质量百分数含量为30%、不同稠化剂含量的5种磁流变脂,考察了不同稠化剂含量对磁流变脂屈服应力、储能模量、损耗模量及磁流变效应的影响。结果表明,磁流变脂表现出剪切稀化的假塑性流体特征,不同稠化剂含量磁流变脂的屈服应力与磁场强度呈现出幂律关系,在适宜稠化剂含量时,幂律指数达到最佳值。提出评价磁流变脂的磁流变效应、交联结构体系强度和稳定性的参数指标,通过调节稠化剂的含量可改变非磁性骨架结构的密度,优化磁性部分对磁流变脂结构强度的贡献,改善磁流变脂的磁流变效应,拓宽磁流变脂的储能模量在磁场下的可控范围。     

各向同性磁流变橡胶材料的摩擦实验研究

分别从宏观和微观角度研究磁场对各向同性磁流变橡胶摩擦性能的影响。搭建了磁流变橡胶的摩擦实验平台,在外加磁场下进行滑动摩擦实验。实验结果表明,磁流变橡胶在轻载且低速条件下,摩擦系数随正压力增大呈减小趋势,而且磁场会使得磁流变橡胶表面的摩擦系数减小,且减小趋势随羰基铁粉体积比的增加呈现非线性变化,当羰基铁粉体积比为10%、正压力为0.25N、磁场强度为250mT时,其摩擦系数变化最大,减小约25%。通过金相显微镜进一步观测施加磁场前后的磁流变橡胶表面,检测表明磁场使得羰基铁粉在磁流变橡胶表面产生聚集,从而使其表面材料属性及微结构发生变化,该变化是促使磁流变橡胶的摩擦性能发生改变的重要原因。     

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.     

Effect of Permeable Crystalline Material on Steel Reinforcement Corrosion of Concrete

Permeable crystalline materialcan permeate into pores and cracks of concrete and catalyze the reaction between Ca(OH) 2and unhydrated cement to generate a great quantity needle non-soluble crystals, which can stop up the pores and cracks of concrete, and increase the impermeability of concrete. This paper reported the results of a study conducted to evaluate steel reinforcement corrosion of concrete specimens uncoated and coated with permeable crystalline material as well as mixed with the permeable crystalline material. The properties evaluated for corrosion test were water impermeability, water absorption, compressive strength and potential. The results of water impermeability, water absorption, compressive strength clearly showed that the permeable crystalline material could prohibit water, any soluble salts and moisture from penetrating the concrete to cause corrosion, leaking, and other problems, and it did increase the compressive strength, which was favorable for protection of corrosion of reinforcing steel. Moreover, it was concluded from the potential-time curve that the steel reinforcement of uncoated specimen was in the state of activation whereas that of other specimens coated and mixed with the permeable crystalline material was in the state of inactivation. Above all, it was indicated that the permeable crystalline materialis very effective to protect the steel reinforcement of concrete from corrosion.     

The Research and Application About "Dry Peeling Off" Technology for Airplane Surface Paint Layer

In this paper, the principle of spurting take off lacquer were introduced; and with orthogonal method the unsaturate polyester was prepared ;it was easy to peel airplane paint layer off with this material and equipment.     

Quality Study of Honeycomb Core Shaping Without Wax Stabilization

Sandwich panels utilizing honeycomb cores result in lightweight, high-strength units that are very rigid. Indeed, they give honeycomb panels the best strength-to-weight ratio of any construction type available. Conventionally, the wax is poured into the cell of the core to strengthen the structure and prevent the core from being crushed during milling. Much time and labor is required to wax, mill, and clean the cores. In this study, the process of pouring wax into the core was skipped. In other words, the cutter directly milled the core. Experiments showed that the compressive strength of the core produced without wax stabilization was only 3% lower than that of cores produced using the traditional method. In addition, the drum peel strengths of cores produced without wax stabilization were 38.4% higher than cores produced using the traditional method, in which residual wax seriously polluted the adhesive. It was also found that eliminating the wax process can reduce costs.     

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.     

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.     

Early ironwork in Biscay: Survey,excavation, experimentation and materials characterization. An integral study of the mountainside ironworks (ferrerías de monte or “haizeolak”)

ABSTRACT

The production of iron in Biscay (Basque Country, Spain) has been a hallmark of this territory of the North of the Iberian Peninsula throughout its history. The Archaeology team of the Basque Country Mining Museum has spent 13 years, so far, studying the origins of this activity through the evidences left at the old pre-hydraulic iron production workshops known as mountainside ironworks (ferrerías de monte) or haizeolak. It has catalogued 170 archaeometallurgical sites of this type in Biscay, and the archeological excavation of some of them has led to the knowledge of the different stages of the production process that took place in these workshops. The team has also experimentally reproduced the work carried out in a mountainside ironworks from the High Middle Ages, and it has currently started the characterization process of this type of activity through the study of the collected materials.     

In-process thermal treatment of polylactic acid in fused deposition modelling

Polylactic acid (PLA) is one of the most widely used open source fused filament fabrication materials due to its ease of extrusion, biodegradability, and mechanical strength. The mechanical strength of PLA largely depends on the proper growth of its semi-crystalline structure, which can be severely impaired by a low rate of crystallization, particularly in open source printers. This can be further aggravated by the non-uniform thermal distribution of heat that causes improper curing among the extruded beads of the printing material. As a result, PLA printed on open source printers does not achieve the best mechanical properties. This research, for the first time, proposes an additive-free solution implemented through a detailed set of experimentation to improve the curing rate through in-process temperature variations to cure the joints among the beads. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy is used to confirm the improvements in the bead joints. This work is conducted in two phases of experiments. In the first phase, a full factorial ANOVA is used to investigate various process parameters and the important variables are used in the second phase to print test specimens in four different sets.