基于细观结构的2.5维机织复合材料强度预测模型

采用经纱矩形截面及纬纱六边形截面假设,将经纱的屈曲轨迹简化为折线形式,建立了2.5维机织复合材料单胞几何模型。以单胞为研究对象,引入改进的三维Hashin失效准则和Mises准则作为组分材料的失效判据,采用不同的刚度退化方式来表征不同的失效模式,建立了基于逐渐损伤理论的强度预测模型。利用有限元分析（FEA）技术,开发了相应的参数化2.5维机织复合材料逐渐损伤分析程序,预测了浅交弯联结构不同机织参数2.5维机织复合材料的拉伸强度,并模拟了经向拉伸和纬向拉伸的损伤扩展过程。与静拉伸试验结果相比,拉伸强度的预测误差在10%以内;模拟的失效模式与试验结果吻合较好。     

2.5维机织复合材料的强度特性

针对浅交弯联和浅交直联两种2.5维机织结构,采用VARTM工艺制备了试验件并进行了强度性能测试,通过对其拉伸后的试样进行切片和断面的SEM观察,研究了拉伸过程中复合材料内部的破坏机理。实验结果表明:在相同纱线排列密度情况下,浅交直联结构的经、纬向拉伸强度明显高于浅交弯联结构;随着纱线层数的增加,两种结构的经向拉伸强度均增大,而纬向拉伸强度则有所波动;对于不同结构的2.5维机织复合材料在单一拉伸载荷作用下,表现出不同的损伤模式,且损伤的初始位置和扩展路径具有一定的分散性。     

2.5维机织复合材料经向拉伸弹性模量预测与试验验证

采用沿经向切片积分的方法计算2.5维机织复合材料的宏观经向拉伸弹性模量, 与试验结果和传统的体积平均合成方法进行了对比, 分析表明, 本文中的方法能够有效提高传统体积平均法的预测精度。利用文中的方法分析了2.5维机织复合材料沿在机织循环过程中的经向拉伸弹性模量分布情况, 并且对相关机织结构的2.5维机织复合材料进行了试验研究。研究发现, 经纱弯曲程度较小的直联结构和添加平直经纱的衬经结构能够有效提高2.5维机织复合材料的经向拉伸弹性模量, 并且能够改善经向拉伸应力-应变曲线的非线性。     

2.5维机织复合材料经向拉伸弹性模量预测与试验验证

采用沿经向切片积分的方法计算2.5维机织复合材料的宏观经向拉伸弹性模量,与试验结果和传统的体积平均合成方法进行了对比,分析表明,本文中的方法能够有效提高传统体积平均法的预测精度.利用文中的方法分析了2.5维机织复合材料沿在机织循环过程中的经向拉伸弹性模量分布情况,并且对相关机织结构的2.5维机织复合材料进行了试验研究.研究发现,经纱弯曲程度较小的直联结构和添加平直经纱的衬经结构能够有效提高2.5维机织复合材料的经向拉伸弹性模量,并且能够改善经向拉伸应力-应变曲线的非线性.     

三维六向编织复合材料渐进损伤模拟及强度预测

基于三维六向编织复合材料的细观结构,假设第六向纱线的截面形状为菱形,建立了三维六向编织复合材料的渐进损伤有限元模型。采用Linde等提出的失效准则,引入周期性位移边界条件,对三维六向编织复合材料的纵向拉伸应力-应变行为进行了渐进损伤数值模拟,讨论了单胞模型在纵向拉伸载荷作用下的细观损伤起始、扩展和最终失效的演化过程,并预测了材料的拉伸强度。在此基础上,进一步研究了编织角、纤维体积分数和编织纱水平取向角等参数对材料纵向拉伸力学性能的影响规律。研究结果表明,三维六向编织复合材料的轴向纱线拉伸断裂是导致其破坏的最主要因素。所得数值结果与现有试验值吻合较好,验证了该模型的有效性,为更深入研究此类材料的力学性能奠定了基础。     

各向异性复合材料开孔板拉伸强度预测及模型验证

基于有限断裂力学方法建立了一种预测多向复合材料开孔板拉伸强度的通用和半经验模型。该模型同时采用基于应力形式的失效准则和基于能量形式的失效准则预测失效。模型仅需铺层弹性常数、无缺口层合板的强度以及0°铺层的断裂韧性等参数。基于线弹性断裂力学建立了多向复合材料层合板的断裂韧性与0°铺层断裂韧性之间的关系, 进而预测了任意铺层复合材料开孔板发生纤维主导拉伸失效时的强度。将模型预测结果与开孔板拉伸强度的试验数据进行了对比验证, 预测误差最大为9.7%, 与点应力和平均应力等方法的对比表明, 该模型的预测精度高于传统的特征长度方法。      

2.5D机织复合材料冲击后剩余强度研究

本文主要对2.5D机织复合材料冲击后的剩余拉伸强度进行研究。采用落锤法预制冲击损伤,并进行剩余拉伸试验。用了基于层合板理论的软化夹杂法对冲击后试样进行刚度衰减的模拟,用有限元软件根据点应力破坏准则计算得到剩余强度,并与剩余拉伸试验结果进行比较,验证了模型的有效性。为便于对比,对平面机织斜纹布铺设的层合板进行了同种计算和实验,得到了在相同冲击能量下2.5D机织复合材料剩余拉伸强度衰减比例小于层合材料的结论,证明2.5D机织复合材料由于Z方向经纱的存在因而具有良好的抗冲击性。     

复杂面内应力状态下平面编织高铝纤维增强氧化铝基复合材料强度及疲劳寿命预测方法

针对平面编织氧化铝基复合材料提出了一种复杂面内应力状态下的强度准则和疲劳寿命预测方法。通过拉伸、压缩及纯剪切试验,分别获得了材料的静强度指标。考虑材料拉、压性能的差异和面内拉-剪联合作用对材料强度的影响机制,提出了修正的Hoffman强度理论。采用该强度理论预测得到的偏轴拉伸强度与试验结果基本一致,偏差不超过10%。开展了偏轴角θ=0°、15°、30°、45°,应力比R=0.1,频率f=10 Hz的拉伸疲劳试验,试验结果表明随着偏轴角的增加,相同轴向拉伸载荷下的疲劳寿命逐渐降低。由于面内剪切应力分量的作用,疲劳失效由纤维主导逐渐过渡到纤维和基体共同主导的模式。基于单轴疲劳寿命曲线,采用Broutman-Sahu剩余强度模型表征剩余强度随疲劳循环次数的变化规律,结合剩余强度演化模型和修正的Hoffman强度理论,提出了一种面内复杂载荷条件下的疲劳寿命预测模型,并引入疲劳剪切损伤影响因子表征拉-剪应力联合作用对材料疲劳行为的影响。采用本文提出的疲劳寿命预测模型,预测不同偏轴角拉伸疲劳寿命,预测结果与试验结果基本一致,偏差在1倍寿命范围内。比较结果表明在给定应力比、温度和疲劳载荷频率条件下,该疲劳寿命预测模型可以用来预测平面编织氧化铝基复合材料拉-剪复杂面内载荷条件下疲劳寿命。      

复合材料跨尺度失效准则及其损伤演化

提出了一种新的基于物理失效模式的复合材料跨尺度失效准则,从细观层面分别对纤维和基体的失效模式进行了表征,将纤维失效分为拉伸失效和压缩失效,将基体失效分为膨胀失效和扭曲失效.建立了相应的失效准则及损伤演化方法.通过正方形和六边形的代表体积单元(RVE)模型,计算了宏观应力到细观应力的机械应力放大系数和热应力放大系数.以IM7/5250-4复合材料拉伸试验作为算例对失效模型进行了验证.计算结果与试验结果吻合较好,表明跨尺度失效准则能够准确预测复合材料层合板的破坏.     

复合材料跨尺度失效准则及其损伤演化

提出了一种新的基于物理失效模式的复合材料跨尺度失效准则, 从细观层面分别对纤维和基体的失效模式进行了表征, 将纤维失效分为拉伸失效和压缩失效, 将基体失效分为膨胀失效和扭曲失效。建立了相应的失效准则及损伤演化方法。通过正方形和六边形的代表体积单元(RVE)模型, 计算了宏观应力到细观应力的机械应力放大系数和热应力放大系数。以IM7/5250-4复合材料拉伸试验作为算例对失效模型进行了验证。计算结果与试验结果吻合较好, 表明跨尺度失效准则能够准确预测复合材料层合板的破坏。     

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.……     

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.     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

Mechanism Study on the Wear of CrAlTiN Coated High-Speed Steel Twist Drills Under Dry Cutting Conditions

As demands about environment protection are growing up, dry cutting technology is getting more and more concerns from all over the world. Main works performed here are study on dry cutting performances and wear mechanisms of M2high-speed steel (HSS) twist drills with CrAlTiN multicomponent coatings, which was deposited using magnetron sputter ion plating system, in drilling 45 and 30CrMnSiA steel, and their comparisons to those in drilling the same steel but using monolayer CrN and commercial TiN coated drills. Drilling performances of drills are evaluated mainly through the measurements of width on outer corner flank land and the cutting forces. Results show that performances of CrAlTiN coated drills are better than those of monolayer CrN and TiN coated drills. In drilling 45 and 30CrMnSiA steel, the average tool life of the CrAlTiN coated drills are 17.2 and 11.8 times higher than those of the uncoated drills. Observing wear of the drill with scanning electronic microscope, results show that there is no crack or spallation of the CrAlTiN coatings in wear zones. Main mechanism of the wear here is adhesion.     

Structural Characteristics of TiO2 Ceramic Coating by Micro-Plasma Oxidation

TiO2 ceramic coatings with thickness of 20 μm were formed on the surface of pure titanium by micro-plasma oxidation. Their micro-structures were investigated by by using X-ray diffraction and their surface images were detected by using scan electronic microscope. There were three kinds of TiO2 coatings, pure anatase type TiO2 phase, mixed phases consisted of rutile type TiO2 phase and anatase type TiO2 phase, pure rutile type TiO2 phase. The coating surface with the pure anatase type TiO2 phase is rough, while the coating surface with the pure rutile type TiO2phase is smooth. The upper coating surface with the mixed type TiO2 phases is anatase type TiO2 structure and the subsurface of the TiO2 coating is rutile type TiO2structure.