2D-C/SiC复合材料开孔件拉伸强度有限元计算

对2D-C/SiC复合材料开孔试件最小净截面图像进行观测,获得试件材料内部宏观孔洞的分布形态及密度分布梯度。通过对2D-C/SiC复合材料拉伸应力-应变行为进行非线性拟合,并利用理论模型计算与实验验证相结合的方法得到了材料密度与其拉伸模量和强度的关系,描述了不同密度2D-C/SiC复合材料的拉伸应力-应变行为。在此基础上,将制备工艺造成的试件材料密度分布的非均匀性和材料拉伸应力-应变行为的非线性引入到有限元模型中,进行开孔试件拉伸剩余强度模拟计算,预测结果与实验结果吻合较好。     

玻璃纤维-铝合金正交层板的拉伸性能研究

通过对两组具有不同铺层次序的玻璃纤维-铝合金正交层板进行拉伸实验,对比研究了铺层次序对材料拉伸力学行为的影响.载荷跌落前两组试件的拉伸力学性能和应力-应变曲线基本一致,说明玻璃纤维-铝合金正交层板的拉伸力学性能与纤维的铺层次序无关.提出了修正后的金属体积分数理论,准确预测了材料的弹性模量、屈服应力及拉伸强度.依据声发射数据和试件损伤失效形貌照片,分析了两组试件的拉伸损伤失效进程.结果表明,铺层次序的不同使得两组材料的损伤进程和破坏模式具有很大差异.最后,利用有限元方法对试件的拉伸力学行为进行了模拟分析,模拟结果与实验值吻合较好.     

含切口复合材料层合板拉伸应变集中与失效分析

通过对圆形切口和长条形切口复合材料层合板试件进行拉伸实验,研究中心切口形状对层合板力学性能的影响。根据实验测得的应变分布规律确定切口引起的应变集中,并分析层合板的破坏过程。建立了基于连续刚度退化准则的渐进损伤模型,分析含切口试件的损伤扩展进程。结果表明,渐进损伤分析模型可准确描述含切口层合板的拉伸失效行为;长条形切口引起的应变集中系数较高,但切口附近的应变梯度更大;两种中心切口形式的复合材料层合板损伤进程有较大差异,但两者的拉伸强度较为接近。     

损伤形式对三维编织复合材料拉压性能的影响

通过对损伤前后三维编织复合材料试件进行纵向拉伸和压缩实验, 分析了材料的拉、压刚度和强度的变化规律和失效形式。主要讨论了4 种损伤加工方案, 包括沿宽度方向单边切割、沿宽度方向双边切割、沿厚度方向单边切割及沿宽度和厚度方向同时切割。实验结果表明, 宽度方向损伤对拉伸强度、模量和压缩强度影响不大, 压缩模量下降了20 %左右; 厚度方向损伤对纵向拉伸、压缩强度和模量影响较大。编织角20°时, 拉伸、压缩应力-应变曲线接近于线性, 试件的失效方式趋向于脆性破坏; 编织角35°时, 压缩应力-应变曲线表现出一定的非线性。      

二维编织陶瓷基复合材料偏轴拉伸力学性能预测

基于二维编织C/SiC复合材料的细观结构,建立了碳纤维丝/热解碳界面/SiC基体和纤维束/表层SiC基体两种尺度下的细观单胞模型,通过有限元方法计算碳纤维丝/热解碳界面/SiC基体模型的等效弹性常数和强度,然后代入纤维束/表层SiC基体模型中计算,并引入Tsai-Wu失效准则,考虑不同失效模式的损伤,建立了二维编织C/SiC复合材料的渐进损伤模型,模拟了其偏轴拉伸应力-应变行为。针对该模型,阐述了二维编织C/SiC复合材料单胞模型在复杂应力状态下其纤维束的损伤过程。数值模拟结果与实验数据吻合较好,验证了模型的有效性,为该种材料的力学性能分析提供了一种有效方法。     

2D-SiC/SiC复合材料拉伸加卸载行为

为了研究国产2D-SiC/SiC复合材料的拉伸损伤行为以及低周循环载荷作用下的力学性能,通过试验和建立加卸载细观力学模型,对其拉伸加卸载行为进行了探讨。建立了单向连续纤维增强陶瓷基复合材料加卸载细观力学模型,得到了初始加载、卸载和重新加载时的应力-应变关系;利用断裂统计方法得到了基体裂纹数随应力变化的关系和复合材料失效判断条件。经过应力转化,将该模型应用于国产二维编织SiC/SiC复合材料。对单向加载试件,采用正交试验方法和最小二乘法得到基体Weibull模量和界面剪切阻力,通过控制材料失效强度与试验结果一致,得到纤维Weibull模量。由上述参数确定的2D-SiC/SiC复合材料拉伸循环加卸载应力-应变曲线与实测曲线吻合很好。通过Matlab编程得到2D-SiC/SiC复合材料单向加载时基体开裂过程图。结果表明,2D-SiC/SiC复合材料失效时,基体裂纹分布相对比较均匀;基体裂纹数随应力单调增加,未出现持平段,表明材料失效时,基体裂纹还没有达到饱和。     

2D-C/SiC复合材料偏轴拉伸力学行为研究

通过对2D-C/SiC复合材料试件进行不同偏轴角度的拉伸实验,研究了偏轴角度对材料拉伸力学特性的影响。通过应变片分别测得了材料加载方向和纤维束方向上的应力-应变行为,对比分析了偏轴角度对上述应力-应变行为的影响;并结合试件断口扫描电镜照片,阐释了纤维束方向上拉伸和剪切损伤间的相互耦合效应。实验结果表明,材料的拉伸模量和强度随偏轴角度的增大出现明显下降;材料纤维束方向上的拉伸损伤和剪切损伤具有显著的相互促进作用。最后,以材料0°拉伸和45°拉伸实验数据为基础,建立了材料的偏轴拉伸应力-应变行为预测模型,模型预测结果与实验结果吻合较好。     

平纹编织SiC/SiC复合材料多尺度建模及强度预测

连续SiC纤维增强SiC基体复合材料（SiC/SiC）具有优异的高温力学性能、辐照稳定性及较低的氚渗透率,在核工程结构领域具有良好的应用前景,掌握其承载状态下的损伤演化和强度性能,对SiC/SiC复合材料的应用具有重要指导意义。本文基于平纹编织SiC/SiC复合材料的制备过程和组分材料分布的多尺度特性,考虑复合材料微观结构的局部近似周期性,建立了纤维丝尺度和纤维束尺度单胞模型。使用有限元分析软件对纤维丝尺度模型的弹性性能和强度性能进行预测,将这些性能参数代入纤维束尺度模型,引入Tsai-Wu失效准则,根据材料的不同失效模式并对失效单元进行方向性刚度折减,模拟了平纹编织SiC/SiC复合材料在单轴拉伸载荷下的渐进损伤过程。数值模拟曲线与试验曲线吻合较好,实现了对平纹编织SiC/SiC复合材料强度的有效预测。      

CALL混杂复合材料裂纹尖端损伤区实验研究

本文用以高密度光栅技术为基础的云纹干涉法对带双边裂纹的CALL混杂复合材料进行了拉伸实验研究,得到了在纤维方向和垂直纤维方向拉伸时双边裂纹尖端损伤区的形状及其应变场分布。结合对试件断口形貌的扫描电镜观察,分析了两种拉伸试件的破坏模态。所得实验结果为进一步深入研究CALL混杂复合材料的损伤和破坏机理提供了重要依据。     

复合材料层合板缺口强度的CDM三维数值模型

针对复合材料层合结构缺口强度问题,基于连续损伤力学（CDM）提出了一种三维损伤数值模型。模型区分了层内损伤（纤维失效、纤维间失效）和层间分层损伤的不同失效模式。采用三维Puck准则与Aymerich准则对上述2类损伤进行判定,材料失效后基于CDM中线性软化模型对材料损伤进行演化。模型考虑了复合材料层合板子层的就位效应和剪切非线性行为。对Carlsson的AS4/3501-6缺口拉伸强度试验进行数值模拟。结果表明:分析结果与试验结果吻合良好,证明了该模型能够准确地预测含缺口复合材料层合板面内拉伸强度。      

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.     

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.……     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

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.     

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.