短纤维交错排布复合材料沿轴等效模量的理论预测

该文针对高性能短纤维交错排布复合材料的刚度预测发展了三维"拉伸-剪切链"模型,并通过了有限元(FEM)计算验证,能够合理地预测短纤维交错排布复合材料的等效模量。验证结果显示,对于纤维长细比的变化、纤维体积含量的变化、纤维和基体间弹性模量比的变化,三维"拉伸-剪切链"模型都可以给出合理的预测,为短纤维交错排布复合材料的刚度设计提供了理论指导和参考依据。研究还显示,同样纤维体积含量和长细比下短纤维交错排布复合材料的等效模量远大于短纤维对齐排布的等效模量,说明了短纤维交错排布结构的优越性。     

多层次等效的Mori-Tanaka法预测含空腔点阵增强芯层的等效弹性模量

提出了兼具力学和声学性能的夹层吸声复合材料-含空腔点阵增强夹芯结构;为了预测含空腔点阵增强结构芯层的等效弹性模量,建立了包含空腔、点阵增强柱和泡沫基体的三相复合材料的细观力学多层次等效数理模型,结合点阵增强柱和空腔周期性分布的特点建立代表性体积单元,利用Mori-Tanaka方法进行两次单相夹杂等效处理,获取了含空腔点阵增强芯层等效弹性模量的解析解,与试验数据和细观力学有限元法结果对比均吻合较好。采用有限元软件ANSYS建立了含空腔点阵增强夹芯结构的实际模型和等效模型,并将芯层等效模量解析结果作为等效模型芯层的材料参数,计算弯曲变形和固有频率并进行对比分析,弯曲变形位移和中低频固有频率的相对误差不超过2%,满足工程精度要求。进一步利用该等效方法,分别探讨了点阵增强柱和空腔体积比对芯层等效弹性模量的影响规律。结果表明,上述方法能较准确地预测含空腔点阵增强结构芯层的等效弹性模量,且数理模型清晰,公式简单,计算快速。     

复合材料热传导系数均匀化计算的实现方法

均匀化理论可以有效预测周期性结构复合材料的等效热传导系数,然而其控制方程的载荷项形式特殊,通用有限元软件中没有对应的载荷形式,难以直接求解.提出一种本构关系及场变量的类比方法,证明了在此类比下等效热传导系数均匀化方程与等效弹性模量均匀化方程是等价的.根据求解等效弹性模量均匀化方程的热应变法,提出一种新的等效热传导系数均匀化方程数值求解方法.以ABAQUS为平台,预测单向纤维复合材料以及金属蜂窝夹芯板的等效热传导系数,计算结果与参考值吻合良好.该方法为基于通用有限元软件的复合材料等效热传导系数的均匀化计算提供了简便途径.     

原位生长碳纳米管增强复合材料风机叶片性能预测

本文采用均匀化理论,结合有限元方法,预测了碳纤维表面原位生长碳纳米管增强复合材料风机叶片的等效性能。根据实验分析,将碳纳米管/碳纤维增强复合材料风机叶片内部结构分别用宏观、细观和纳观三个层次来描述。利用APDL编写的均匀化计算程序,分析了碳纳米管的长度、直径以及弹性模量对复合材料等效性能的影响。计算结果表明,随着碳纳米管长度的增加,复合材料的等效性能增加;当长度一定时,增加碳纳米管的直径和弹性模量,也能提高复合材料的性能。本文结果对复合材料风机叶片的制备有一定的指导作用。     

短纤维增强注塑制品的力学性能分析

将短纤维增强注塑制品看作多层板并分析了注塑制品的有效弹性性能.采用Tandon-Weng模型计算了单取向短纤维增强复合材料的弹性性能,采用取向平均法计算了具有任意平面取向的单层板材料弹性常数,运用层合板理论建立了短纤维增强注塑材料的有效弹性模量计算模型.测定了特制试样中的纤维取向分布,计算了有效弹性模量,并与实验结果对比证明这种方法是有效的.     

δ-Al2O(3f)/Al基复合材料弹性模量的有限元能量法预测

基于能量等效原理, 采用三维有限元方法, 考虑短纤维位向的随机分布对复合材料弹性模量的影响, 利用有限元能量法对δ-Al₂O_(3f)/Al 合金复合材料的弹性模量进行了预测。预测结果与实验结果和目前常用的几种预测方法进行了比较, 表明该方法是合理、准确的。     

原纸弹性模量和屈服强度的测定方法

原纸弹性模量和屈服强度是进行后续各种相关分析必需的性能指标,如何客观准确地测定这2个指标至关重要。在分析已有研究所用测定弹性模量方法存在缺陷的基础上,提出了一种以微分-区限变分法替代传统方法求解原纸弹性模量和屈服强度的方法。并以某定量为105g/m2的瓦楞原纸为例,利用微分-区限变分法计算出该瓦楞原纸的弹性模量为2.51GPa,屈服强度为5.11MPa。微分-区限变分法能客观确定线性段结束的关键点,因而能够更加准确简便地计算原纸的弹性模量和屈服强度。     

金属基复合材料微屈服行为的力学分析与试验

本文采用细观力学计算、有限元分析和试验测试等方法,定量研究了短纤维增强金属基复合材料微屈服过程中应力应变分布和微屈服规律,结果表明不同短纤维分布朝向、体积比的Al2O3-SiO2(sf)/Al-Si复合材料微屈服行为符合Brown-Lukens关系,在增强体短纤维附近存在较大应力集中,晶粒直径、位错密度等材料参数对等效应力影响不大,对等效塑性应变有显著影响,同时分析了增强体短纤维的体积含量和短纤维分布状态对材料微屈服强度的影响。     

等效介质理论数值法计算复合材料的热膨胀系数

本文用一套等效介质理论的数值方法计算了球状微粒掺杂之各向同性复合材料及单向纤维增强之横观各向同性复合材料之线热膨胀系数,得到合理的结果,并与Schapery式、Kerner式之计算及实验值作出比较,显示了等效介质理论于复合材料热弹性能计算之适用性.      

短纤维复合材料热-机械特性研究

借助于Eshelby等效夹杂法,本文推导了含椭球形短纤维复合材料热膨胀系数及短纤维体内外应力场的计算方法。计算了温度变化?T时,短纤维附近的应力值及复合材料热膨胀系数的变化情况,数值计算结果说明,长椭球形纤维导致复合材料热—机参数呈非线性变化,而扁椭球纤维所导致的热——机参数呈近似线性规律变化。     

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