预成型体渗透率预测及其受压缩变形的影响

建立了织物预成型体单胞内纱线间细观流动和纱线内部微观流动的统一的数学模型。基于最小势能原理建立了织物松弛状态下的单胞几何模型,同时对在模具压缩下的单胞变形进行了分析,并建立了不同压缩状态下的单胞几何模型。通过对单胞内树脂流动数学模型的数值求解,获得了流动速度场及压力场,进而预测了预成型体的渗透率。预测1组不同压缩状态下的单胞渗透率,研究了预成型体压缩变形对渗透率的影响。结果显示:随着压缩量的增加,其渗透率逐渐降低。通过实验测量及数据分析,验证了建模和预测方法的正确性。     

微-细双尺度单胞下织物预成型体渗透率预测

建立了描述双尺度单胞内树脂流动的数学模型,基于最小势能原理建立了织物单胞逼近真实的几何模型。研究了由纱线卷曲和相互挤压引起的微观渗透率分布的不均匀性及其在流动求解上的处理方法; 基于有限差分法建立了树脂流动控制方程数值求解方法,并开发了相应软件包,求得了单胞内树脂流动压力和速度场,进而获得了渗透率预测值; 通过与文献预测数据和实验值对比,证明了本文中预测模型和求解方法的正确性。     

树脂传递模塑成型工艺中嵌套效应引起渗透率变异的实验与数值模拟

树脂传递模塑成型工艺(RTM)中最重要的变形模式之一是厚度方向压缩。厚度方向压缩减小了织物预成型体的厚度,使织物预成型体局部结构形式发生改变从而引起嵌套效应。嵌套效应不仅会减少织物预成型体的厚度,增加纤维的体积分数并改变孔隙率,而且相邻织物层嵌套效应具有一定的空间分散性,从而使得织物预成型体渗透率具有变异性。本文针对低黏度树脂设计了一种实验装置用以测量局部渗透率的空间分散性,随后建立了随机嵌套单胞模型,利用ANSYS/CFX有限元软件实现了单胞填充浸润的数值模拟,通过流量分析获得局部渗透率,并研究了渗透率的统计分布。通过实验结果与数值模拟结果相对比,验证数值模拟结果的可靠性。最后,基于渗透率的统计分布建立了随机渗透率场,并进行填充浸润的数值模拟,通过与传统恒定渗透率的方法进行比较,证明该方法具有更高的先进性。研究结果可以对未来RTM工艺的稳健性优化提供依据。      

预浸织物剪切变形时树脂细观分析模型

为了更好地研究在发生剪切变形时预浸织物材料的力学性能,建立了在像框剪切试验时未固化的树脂对织物发生剪切变形时的阻碍作用的细观分析模型.通过对材料的单胞进行分析,得到了织物单胞变形前、后各质点间的运动学关系,进而得到了树脂材料对整个织物单胞的阻力矩,即树脂的阻尼作用.此阻尼作用较好地说明了树脂在预浸织物材料中的作用.此外,通过树脂的流变试验得到其粘性系数,该粘度系数确定,即该材料的阻尼作用确定.     

基于多相流的LCM工艺气泡生成仿真

分析了液体模塑成型工艺（LCM）下织物预成型体中双尺度流动以及由此造成的空气裹入,进而产生细观及微观气泡的现象。基于多相流（VOF）方法建立了树脂空气两相流体在单胞内部流动的数学模型,并确定了该模型中多孔介质阻力源项和毛细力源项的具体形式。基于Fluent软件的UDF功能实现了上述两相流模型的数值求解,研究了平纹织物单胞中的两相流动以及2种气泡的生成过程。对Rovcloth 2454织物的气泡生成仿真结果显示,毛细数 Ca 对气泡的产生有决定性作用：当毛细数接近临界毛细数 Ca^c时,气泡产生量最低,而当Ca小于Ca^c时,容易产生细观气泡,反之容易产生微观气泡。通过与文献中的理论预测和实验数据对比,验证了本文算法的正确性。     

无弯曲纤维织物面内渗透率的结构相关性

建立无弯曲纤维织物(Non-crimped fabrics, NCF)的几何结构单胞, 应用树脂在纤维束内与束间耦合流动的模型, 数值模拟树脂的细观流动行为, 结合Darcy定律, 计算单胞的面内等效渗透率, 并对计算方案进行验证。在此基础上, 探讨织物的纤维束间距离、纤维束高度以及束内渗透率等细观结构参数与单胞面内等效渗透率之间的关系。结果表明: 单胞面内等效渗透率随纤维束间距离的增大而增大, 其倒数的对数之间呈正的线性关系; 纤维束高度对单胞面内等效渗透率的影响类似于纤维束间距离对其的影响; 单胞面内等效渗透率随纤维束内渗透率的增加而线性增加。      

复合材料液体模塑成型工艺中预成型体渗透率张量的数值预测

结合均匀化理论和计算流体动力学技术, 实现了对复合材料液体模塑工艺中预成型体渗透率张量的预测。首先, 采用均匀化理论分析了流体在多孔介质内的流动问题, 推导出广义达西定律, 证明以施加周期性边界条件的单胞为研究对象, 可以预测预成型体的渗透率张量, 并以单向纤维织物为例, 对该方法进行了验证。对于复杂结构的预成型体, 渗透率的预测分为两步, 首先分别确定预成型体中流道和纤维束的渗透率, 然后计算其整体宏观渗透率。对于二维平面织物, 该方法与其他预测方法及实验的结果吻合较好。本文还考察了单胞的微观结构对渗透率的影响, 微观结构相似的预成型体如果孔隙率相同, 但束间流道的结构不同, 其整体宏观渗透率也存在很大差别。      

液体模塑成型工艺二维径向非饱和流动数值模拟

通过引入沉浸函数建立了双尺度多孔介质非饱和流动模型,并采用有限元/控制体积法实现了恒压及恒流注射条件下液体模塑成型（LCM）工艺二维径向非饱和流动的数值模拟,得到了不同注射条件下纤维织物内的压力场分布及半饱和区域长度随时间的变化规律,并将双尺度非饱和理论结果与单尺度饱和理论结果进行对比。结果表明：非饱和流动过程中,半饱和区域内的压力和压力梯度明显下降;半饱和区域长度随时间逐渐增加随后保持稳定,当流动前沿到达出口后半饱和区域长度开始逐渐减小;当两个主方向渗透率不同时,沿主方向半饱和区域长度也不同,渗透率越大该方向的半饱和区域长度也越大,纤维织物完全浸润时间取决于较小的渗透率。研究结果对合理预测树脂填充过程中压力分布及纤维预制件的浸润具有指导意义。     

正交平面织物球面成型渔网模型的几何分析

为了从理论上表征平面正交织物球面成型后的几何特征, 提出基于坐标变换求解渔网模型的新方法, 确定单层正交平面织物在球面上铺覆成型后的网格位置、 织物剪切变形和纱线弯曲变形。依据弧长不变条件确定方形织物完全包覆球面后的对称面上的网格位置和局部坐标系下中间网格的位置, 利用坐标变换获得中间网格在整体坐标系成型球面上的坐标位置; 根据变形前后的网格形状确定织物面内剪切变形和两个方向纱线的弯曲曲率, 为织物的球面成型性评价提供几何参数。通过实例证明了当网格尺寸远小于球体半径时铺覆变形程度与网格 尺寸无关, 也与球体半径无关。铺覆后织物的剪切变形和纱线弯曲变形分布只与织物在球面上的球坐标位置有关。     

复合材料带筋壁板预成型体压缩性与渗透性对树脂流动的影响

以航空碳纤维增强树脂基复合材料典型结构件带筋壁板为研究对象,通过对U3160单向织物的组织结构进行分析,根据纤维束的受压变形状态对其压缩响应进行理论建模,然后以纤维束压缩模型为基础,预测了U3160单向织物按0°/45°/90°/-45°铺层时预成型体在压缩应力作用下厚度变化的响应行为。建立了压缩应力作用下纤维预成型体的渗透率解析模型:在织物压缩模型的基础上,建立了纤维束等效渗透率模型;根据张量理论,分别建立了0°、±45°和90°铺层织物等效渗透率模型;运用渗透介质串并联关系,建立了带筋壁板各特征区域渗透率综合表征模型。基于PAM-RTM流动模拟软件,进行分区渗透率定义,在充模过程中对树脂在带筋壁板预成型体中的流动行为进行模拟,优化工艺参数,确定出最终充模方案,并制作带筋壁板实验缩比件进行成型实验,验证了充模方案的合理性。研究结果为制件的成功制作提供理论依据,从而指导生产实践。      

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.     

The Influence of Nitrogen and Boron Implant into Silicon Substrate on the Phase and Internal Stress of c-BN Films

Cubic boron nitride(c-BN) film was deposited on a Si (100) substrate by the RF-magnetron sputtering.The mainly problems for fabrication of c-BN films are the low purity and high intrinsic compressive stress. In order to solve the two problems, the c-BN film with the buffer interlayer was deposited on the substrate which had been implanted with nitrogen and/or boron ions. The results show: the implantation of nitrogen ions can obviously increase c-BN content and reduce the internal stress slightly; while the implantation of boron shows no obvious improvement to the content of c-BN, which can reduce the internal stress in the film obviously. In addition, it is suggested that the implantation of nitrogen and boron shows the best result, which not only can increase the content of c-BN, but also reduce the internal stress in the c-BN film obviously.