一种基于钉“超元”的复合材料机械连接钉载计算方法

连接区的设计是复合材料设计中一个很关键的环节, 而确定钉载分布又是多钉接头中的重要问题。本文基于位移法原理, 提出一种以有限元“超元”为基础的钉载分析计算方法, 避免了实验测定复合材料P-D曲线的困难, 同时由于“超元”技术的采用具有较高运算效率。本文方法对接头的几何外形、尺寸、钉的排列方式、外载及边界条件等没有限制。与试验及文献算例结果比较, 证明了本文方法正确、可靠。最后, 利用本文方法对多种情况钉载分配进行了参数研究, 得出一些规律性结论。     

复合材料多钉连接钉载矢量传感器

在总结复合材料多钉连接钉载测试方法的基础上,针对单向载荷传感器应用中必须已知钉载方向且需要按照钉载方向装设传感器的缺点,提出了钉载矢量传感器方案。钉载矢量传感器无预设安装角度要求,能够测量载荷方向;并对钉载矢量传感器的选材、应变片方案及开槽尺寸进行了设计,制造了钉载矢量传感器。采用复合材料单钉单剪螺栓连接,分别对钉载矢量传感器测量结果的线性符合性、重复性、安装角度影响以及载荷方向测量能力进行了测试研究。测试结果表明:钉载矢量传感器满足工程上对载荷分配测试的技术要求,验证了本文所提出的钉载矢量传感器的适用性。     

考虑间隙配合的复合材料钉载分配均匀化方法

针对多钉连接中因复合材料脆性等因素导致结构中的钉载分配不均匀,以及接头在承载较大的钉位置易发生过早破坏的问题,提出了调整钉孔配合间隙改善钉载分配的不均匀性的优化方法。首先,基于弹簧质量模型,以钉孔间隙为设计变量,建立了多钉连接钉载分配的二次规划优化模型。然后,采用内点法对优化模型进行了求解,得到了优化模型的全局最优解。最后,以复合材料5钉双剪接头为例,对钉孔间隙进行了优化,将计算结果与有限元预测结果进行对比。结果表明:模型优化结果与有限元结果吻合较好,优化后最大钉载比例由41.1%降低到了20%。采用该模型可以高效、准确地实现复合材料多钉连接钉载分配比例的均匀化设计。      

GBJM方法的改进及其在含钉群复合材料结构钉载分配和承载能力分析中的应用

为了分析含钉群复合材料结构的钉载分配及承载能力问题,首先对Globle Bolted Joint Model(GBJM)方法进行了改进,然后采用改进的方法对复合材料多钉连接结构的钉载分配和承载能力进行了预测,并与试验结果进行了比较。结果表明:当孔边复合材料未出现损伤时,该方法对多钉载荷分配的预测和试验结果比较接近;而对结构承载能力的预测,该方法偏于保守,比试验结果约低15%。同时该方法具有两个显著优点:一是计算结构钉载分配时效率高,和三维有限元模型相比提高约75%;二是能够对含钉群复合材料结构的失效载荷进行有效的预测。     

碳纤维/树脂复合材料多钉连接钉载系数测试方法

为解决由于碳纤维/树脂复合材料多钉连接结构中钉载分配状态和测试方法不同导致的钉载系数测试分散性不明确的问题,针对应变片和钉载矢量传感器两种测试方法,提出基于不确定度理论的钉载系数相对测量不确定度的计算模型,并计算两种测试方法对碳纤维X850/树脂复合材料单剪、双剪连接结构钉载系数的相对测量不确定度。结果表明,应变片测试方法中,单剪结构钉载系数无法准确测量,双剪结构钉载系数相对测量不确定度通常超过2.8%,且随结构中螺栓数目和应变片贴片角度偏差的增加而增大;钉载矢量传感器测试方法中,单剪、双剪结构钉载系数均可测试,且针对任意螺栓数目结构,其钉载系数相对测量不确定度最大不超过1.5%。      

多钉连接钉载分配特性研究方法

利用金属-复合材料层合板紧固件多钉连接件开展拉伸载荷下钉载分配特性的试验和有限元分析研究。试验件为一列三钉单搭接和双搭接连接件。通过应变电测技术获得连接件典型截面应变分布, 再间接估算钉载分配比例。建立了试验件二维、三维有限元模型, 并计算获得应变和钉载分配结果。对比发现, 应变的计算值与实测值吻合, 但钉载分配的计算结果与实测结果存在较大偏差。分析表明: 基于表面应变测量估计钉载分配的方法不能反映连接件的附加弯矩对多钉钉载分配比例的影响; 采用经过应变测量结果验证的有限元模型, 通过数值计算确定钉载分配是一种可行的技术途径; 而应用简化的板-梁二维有限元模型计算钉载分配可以满足工程精度要求。     

配合方式对复合材料单钉单剪螺栓连接接头刚度的影响及其机制

针对单钉单剪复合材料螺栓连接,研究了间隙与干涉2种配合方式对接头刚度的影响及其机制。通过与试验结果的对比,验证了所采用的有限元方法的有效性。结果表明:对于复合材料单钉单剪螺栓连接,间隙配合导致接头刚度变小, 3%钉直径的间隙量导致接头刚度下降16%~17%,并且随着间隙量的增大,接头刚度基本呈线性下降;而对于装配过程中没有产生孔边分层损伤的干涉配合连接件, 0.5%钉直径的干涉量使得接头刚度增加了约15%。配合方式不同,连接件孔周接触应力峰值方向及厚度方向接触应力分布不均匀的程度不同,进而影响了接头刚度。      

复合材料3钉单搭连接有限元模拟与钉载分布

进行了复合材料一铝合金三钉单搭连接单向拉伸试验,测量了层合板面内位移、应变和离面位移随载荷的变化关系,建立了复合材料多钉单搭连接的三维累积损伤有限元模型,计算与试验对比结果表明,该模型可模拟大范围损伤发生之前的承载特性。采用试验和数值模拟相结合的方法研究了复合材料一金属三钉单搭连接钉载分布情况,结果表明：试验用复合材料-铝合金三钉单搭连接,螺栓1承载比例最高,螺栓3次之,中间螺栓的承载比例最低,并且螺栓承载比例在加载过程中基本保持不变;随着金属连接板刚度的增加,螺栓1的承载比例增加,螺栓3承载比例降低,中间螺栓2的承载比例变化较小,层合板离面位移减小;金属板配合间隙变化对钉载分布影响很小,但层合板的离面位移随配合间隙的增大而增大。     

环境温度和间隙对复合材料-金属混合结构机械连接钉载分配的影响

通过有限元模拟与试验相结合的方式,研究环境温度和间隙对复合材料-金属混合结构连接钉载分配和强度的影响。分别建立双钉单剪和三钉单剪有限元模型,并在模型中综合考虑了接触、金属塑性和复合材料渐进损伤等因素,研究了不同温度和间隙情况下钉载的分配情况。研究表明,间隙对初始阶段钉载分配影响较大,但不影响塑性屈服阶段的钉载比例和承载能力;温度改变引起的热应力会带来额外的温度载荷,温度载荷对端部钉载影响较大,温度载荷与机械载荷叠加,会加剧端部钉载的分配不均。      

复合材料单钉接头三维逐渐损伤破坏分析

针对纤维增强复合材料螺栓双盖板接头, 发展了面内静拉伸三维逐渐损伤模型。并对损伤累积过程中出现的四种基本损伤机理类型(纤维断裂、纤维-基体剪切、基体开裂、分层) 及其之间的相互关联性进行了分析模拟, 并能成功预测其接头层合板静拉伸强度、破坏模式及损伤与扩展的整个过程。同时用参数化设计方法, 对任意铺层、任意尺寸单钉接头进行建模, 使分析工作更加方便。用本模型计算的结果与文献[ 4 ]提供的9 种不同铺层尺寸接头实验结果进行了比较分析, 对比结果非常令人满意。      

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.     

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.……     

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.     

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.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Effect of Oxide Assisted Metal Nanoparticles on Microstructure and Morphology of Gallium oxide Nanowires

Several researches have been reported about the characteristic of β-Ga2O3 nanowires which was synthesized on nickel oxide particle. But indeed, recent researches about synthesis of β-Ga2O3 nanowires on oxide-assisted transition metal are limited to nickel or cobalt oxide catalyst. In this work, Gallium oxide (β-Ga2O3 ) nanowires were synthesized by a simple thermal evaporation method from gallium powder in the range of 700 - 1000℃ using the iron, nickel, copper, cobalt and zinc oxide as a catalyst, respectively. The β-Ga2O3 nanowires with single crystalline without defects were successfully synthesized at the reaction temperature of 850, 900 and 950℃ in all the catalysts. But optimum experimental condition in synthesis of nanowires varied with the kind of catalyst. As increasing synthesis temperature,the morphology of gallium oxide nanowires changed from nanowires to nanorods, and its diameter increased. From these results, we could be proposed that the growth mechanism of β-Ga2O3 nanowires was changed with synthesis temperature of nanowires. Microstructure and morphology of Synthesized nanowire was characterized by HR-TEM, FE-SEM, EDX and XRD.     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from