基于位错密度的钛合金电辅助压缩仿真与实验验证

目的 以新型高强韧Ti?6Cr?5Mo?5V?4Al(Ti6554)近β钛合金为对象,探讨脉冲电流对材料变形行为和温度变化的影响规律,揭示Ti6554钛合金在不同电流密度下的位错密度演化规律。方法 对材料进行不同电流密度、占空比、应变速率条件下的电辅助压缩实验,建立考虑位错密度的修正电塑性本构模型,基于ABAQUS进行UMAT子程序开发,建立电?热?力三场耦合有限元模型,模拟Ti6554钛合金电辅助压缩变形过程,并进行实验验证。结果 随着电流密度和占空比增大流动应力减小,随着应变速率增大流动应力也增大;电辅助压缩实验结果与模拟结果相比的平均误差为6.31%,验证了模型的有效性;通过子程序状态变量输出位错密度的变化发现,电流密度为15.92、23.88、27.87、31.88、39.81 A/mm²的位错密度分别下降了15.34%、55.63%、68.23%、83.84%、89.13%,表明位错密度随电流密度的增大而降低。结论 建立了基于位错密度的电塑性本构模型和电-热-力多场耦合的有限元模型,能够模拟Ti6554钛合金的电压缩变形行为,并且表征了位错增殖、位错湮灭及动态回复,获得了其位错密度的演化规律。     

Ti6554钛合金高温变形行为与微观组织演化机制研究

目的 揭示新型高强韧钛合金Ti-6Cr-5Mo-5V-4Al(Ti6554)在710～910℃和0.001～10 s?1条件下的热变形行为、热加工图和微观组织演化机制.方法 基于Gleeble-3800D热模拟试验和金相观察,基于实测数据拟合Arrhenius型全应变本构模型.结果 建立了本构模型σ=0.0045 ln...     

基于摩擦修正的 TA15 钛合金热变形行为及加工图

目的采用Gleeble-3500热模拟实验机,研究TA15钛合金在变形温度为900~1050℃、应变速率为0.01~1 s-1条件下的热压缩流变行为及变形组织。方法采用一种简单有效的方法修正了TA15钛合金热压缩实验中摩擦引起的误差;计算出了TA15钛合金的应力指数和热变形激活能,建立了含有Z参数的双曲正弦函数形式本构方程;基于Murty准则,建立了其加工图。结果TA15钛合金的热压缩流变行为可采用含有Z参数的双曲正弦函数形式本构方程来描述,其平均变形激活能为625.884 kJ/mol;通过分析热加工图,确定了最优热变形工艺参数为:T=950℃,ε=0.01 s-1。结论研究结果可为TA15钛合金的塑性变形数值模拟提供基础,对合理制定热加工工艺具有重要指导意义。     

新型Ti-Al-Zr-Nb-Mo-Si钛合金热变形行为及基于BP神经网络模型的本构关系研究

通过热压缩模拟实验,研究了一种新型Ti-Al-Zr-Nb-Mo-Si高强度、高弹性模量钛合金在温度为950～1 150℃、应变速率为0.05～1 s~(-1)条件下的流变行为。真应力-真应变曲线表明,变形温度、应变速率对该合金的流变应力影响显著。基于实验数据,利用包含应变参量的双曲正弦型Arrhenius方程和BP人工神经网络模型分别构建了变形参数和流变应力的本构关系,并对两种模型进行了对比评价。结果表明,两种模型的平均相对误差值分别为11.21%和2.163%,整体上均可以较好地预测Ti-Al-Zr-Nb-Mo-Si钛合金热压缩流变应力;但相对传统Arrhenius方程,BP人工神经网络模型具有更高的精度和可靠性。     

不同晶粒尺寸钛合金高温压缩力学行为研究

为了解不同晶粒尺寸钛合金的高温变形力学行为,对α相平均晶粒尺寸分别为6、12μm和20μm的TC4钛合金进行了高温压缩试验,研究了晶粒尺寸和变形参数对TC4钛合金高温压缩力学行为的影响,建立了不同晶粒尺寸TC4钛合金的高温变形本构方程.研究表明:应变速率为10-4s-1时6μm的细晶钛合金出现超塑现象,应变速率在10-3～10-1s-1范围时,变形初期不同晶粒尺寸钛合金的流动应力符合Hall-Petch关系,由于细晶钛合金流动应力软化速度较快,变形至稳态阶段时细晶钛合金流动应力低于粗晶合金.     

TC21 钛合金高温变形本构方程研究

目的研究变形温度、应变速率等热力参数对TC21钛合金流动应力的影响规律,并构建出TC21钛合金本构方程。方法在热模拟试验机上对TC21钛合金进行了等温恒应变速率压缩实验,分析其真应力-真应变曲线。结果获得了该合金在变形温度范围为760~920℃、应变速率范围为0.001~10 s-1的流动应力数据,采用多元线性回归法建立了该合金的本构方程。结论误差分析表明,该本构方程具有较高精度,可为TC21钛合金锻造过程中的数值模拟和锻造热力参数的合理制定提供理论依据。     

Ti−6Mo−5V−3Al−2Fe−2Zr合金热变形行为及热加工图

目的 建立近β钛合金Ti−6Mo−5V−3Al−2Fe−2Zr(质量分数)的热变形本构方程,绘制热加工图,确定该合金的流变失稳区和适宜加工区,为其在工业生产中热加工工艺参数的制定提供指导。方法 在变形温度700~ 850 ℃、应变速率0.000 5~0.5 s⁻¹、真应变0.7的条件下,对近β钛合金Ti−6Mo−5V−3Al−2Fe−2Zr进行热压缩实验;基于Arrhenius方程建立该合金的热变形本构方程,并对方程进行验证;根据Prasad失稳准则,构建该合金的热加工图。结果 该合金的流变应力随着变形温度的升高而减小,随着应变速率的增大而增大;其热变形激活能为226.29 kJ/mol,本构方程为;通过热变形本构方程得到的峰值应力计算值与实验值平均误差为4.21%。结论 建立的热变形本构方程预测了流变应力,描述了该合金的热变形行为;通过叠加合金的能量耗散图和流变失稳图,获得了该合金的热加工图。基于热加工图确定该合金的流变失稳区为变形温度700~755 ℃与784~850 ℃、应变速率0.5~0.05 s⁻¹,最佳加工区为变形温度836~850 ℃、应变速率0.000 5~0.005 s⁻¹。     

TA5钛合金的应变补偿物理本构模型和加工图

使用Gleeble-3800热模拟试验机对TA5钛合金进行等温恒应变速率压缩,研究其在变形温度为850~1050℃、应变速率为0.001~10 s^-1和最大变形量为60%条件下的高温热变形行为;建立了引入物理参量的应变补偿本构模型,并根据DMM模型得到了加工图。结果表明：TA5钛合金为正应变速率敏感性和负变形温度相关性材料;考虑物理参量的应变补偿本构模型具有较高的预测精度,其相关系数R为0.99,平均相对误差AARE为8.95%。分析加工图和观察微观组织,发现失稳区域(850~990℃,0.05~10 s^-1)的主要变形机制为局部流动;稳定区域(870~990℃,0.005~0.05 s^-1)的主要变形机制为动态回复和动态再结晶。TA5钛合金的最佳热加工工艺参数范围为870~990℃和0.005~0.05 s^-1。     

钛合金与钢的电偶腐蚀行为研究

研究了TA28、Ti6321钛合金以及921A、907A船体结构钢在海水环境中的腐蚀特性及电化学行为,对两种钛合金与船体钢之间多面积比条件下的电偶腐蚀行为进行了试验。结果表明,当钛合金与钢直接接触时,钛合金与钢制船体间存在轻微的电偶腐蚀,采用电绝缘措施可以有效控制钛合金对钢制船体的电偶腐蚀。     

TB8钛合金的热变形行为及加工图

采用Gleeble-1500热模拟机在变形温度为750～1100℃、应变速率为0.01～1s-1范围内对TB8钛合金进行了单道次热压缩变形试验,研究了其高温变形力学行为.结果表明:随着变形温度的升高和应变速率的降低材料的峰值应力和稳态应力显著降低;高温变形条件下TB8合金流变应力本构关系可以用双曲正弦方程和Z参数描述;建立并初步分析了基于动态材料模型的TB8钛合金热加工图,当温度为950～1100℃、应变速率为0.01s-1时TB8合金的能量耗散效率较高.     

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.