卫星贮箱安装板复合材料蒙皮热应力工艺设计优化

基于有限元分析方法,对热压罐成型卫星贮箱安装板复合材料蒙皮热应力工艺设计方案进行仿真分析,研究了预浸料铺层区域、均压板结构、固化温度等工艺参数对蒙皮热应力的影响。结果表明,在均压板开孔结构不变,当预浸料铺层方法从整体铺层转变为开孔铺层,最大压缩热应力为-393.7MPa,增加了3.8%;最大拉伸热应力为87.9MPa,降低了62.9%。保持均压板开孔结构-预浸料开孔铺层不变,当固化最高温度从180℃降低到120℃,最大压缩热应力为-250.5MPa,最大拉伸热应力为55.9MPa,最大压缩应力和拉伸应力均降低了36.3%。降低固化温度显著降低热应力,并通过实验验证了分析结果。     

摩擦摆支座在地下地铁车站结构中的减震效果研究

基于阪神地震中大开地铁车站的破坏模式与成灾机理,借鉴地面建筑结构的减隔震设计理念,提出在地铁车站中柱顶部设置摩擦摆支座形成新型减震结构体系。通过建立土-地下结构整体二维数值分析模型,运用整体动力时程分析方法对比研究了摩擦摆支座不同滑道半径和不同摩擦系数工况下减震结构与原型结构在结构变形和截面内力等动力响应的差异。结果表明：柱端设置摩擦摆支座使得结构整体抗侧刚度减小,结构的水平变形呈现小幅增大趋势。当摩擦摆支座的滑道半径越大、摩擦系数越小时,中柱变形、剪力和弯矩值较原型结构均有大幅的减小。     

压弯半径对7A85结构壁板退火展平成形尺寸与组织性能的影响研究

目的 为满足结构舱段用高强高韧铝合金宽幅薄壁高筋整体成形壁板的精密制备需求,在材料退火组织状态下,结合不同压弯半径展平工装,实现7A85结构壁板的展平处理。方法 采用ABAQUS有限元软件计算不同压弯半径下的结构回弹尺寸,采用万能力学性能试验机测试不同区域的力学性能,结合扫描电镜完成组织形貌与断口形貌的观察。结果 随着压弯半径的增大,7A85铝合金结构壁板蒙皮区域的应力峰值持续下降,结构回弹尺寸误差先下降后上升,立筋区域的应力峰值持续下降,结构回弹尺寸误差先下降后上升。当FSW加厚区进行压弯时,随着压弯间隙的增大,应力峰值持续下降,随着压弯半径的增大,应力峰值先上升后下降,结构回弹尺寸误差明显提高。结论 结合7A85铝合金挤压圆筒不同区域金属型退火展平模具,成功制备出了幅长为8 000 mm、幅宽为1 280 mm的7A85铝合金结构壁板。     

槽形截面梁静力学特性的研究

该文综合考虑了槽形梁的剪切变形和剪滞翘曲应力的自平衡条件,以最小势能原理为基础建立了槽形结构三个广义位移的控制微分方程和自然边界条件,获得了相应广义位移的闭合解,提出了一种对槽形梁静力学特性的准确分析方法。算例中详细分析了剪切变形、剪力滞后和自平衡条件等因素对槽形梁挠度和应力的贡献,明确了槽形梁的静力学特点。该文解析解与有限元数值解进行了比较,证明了该文方法的有效性。     

应变梯度弹性理论下微构件尺寸效应的数值研究

根据位移二阶梯度分量的不同,应变梯度理论可以分为偶应力理论和全应变梯度理论。与偶应力理论相比较,全应变梯度理论增加了伸长梯度对应变能密度函数的贡献,因此,该理论预测的尺寸效应要强于偶应力理论预测的尺寸效应。基于建立的应变梯度弹性理论C¹ 自然单元法,研究了微夹持器和拉伸微试件的尺寸效应现象。对于微夹持器,梳状静电驱动臂与固定端之间采用S 形弹簧连接,降低了夹持臂的弯曲刚度,增加了夹持力的有效输出;当弹簧宽度接近材料的特征长度时,无量纲弯曲刚度值很大,微夹持器具有强烈的尺寸效应。对于拉伸微试件,当圆孔半径和椭圆孔长轴接近材料的特征长度时,无量纲应力集中系数很小,微试件尺寸效应明显;随着U 槽端部半径的增加,微试件尺寸效应明显变弱;随着槽深的增加,微试件尺寸效应缓慢减弱。对于微构件的所有计算情况,全应变梯度理论下的尺寸效应强于偶应力理论下的尺寸效应,数值计算结果与理论预测相吻合。     

多级性态隔震体系试验研究和结构动力响应分析EI北大核心CSCD

铅芯橡胶支座力学性能受竖向压应力和水平剪应变影响较大,且在极罕遇地震下传统隔震结构易发生位移过大而引发隔震沟碰撞风险。该文提出一种新型高性能多级性态隔震支座,可在单个支座中兼顾竖向高承载特性和稳定的水平滞回特性,所提出支座具有与结构多水准抗震性能相匹配的多级刚度特性。制作多级性态原型支座并进行力学性能试验,得到多级性态支座不同工况下的水平滞回性能,基于试验结果提出了多级性态支座的力学滞回模型。对某高层框架剪力墙结构进行多级性态隔震设计并与原设计铅芯橡胶支座(lead rubber bearing,LRB)隔震方案对比分析,结果表明多级性态隔震系统具有理想的水平隔震效果,且可有效控制支座的竖向拉应力,在极罕遇地震下有效控制隔震层水平位移,实现隔震结构具有多级的抗震性能。     

汽车空调热力膨胀阀小型化感温元件中膜片结构优化

针对小型化感温元件中膜片行程不足的问题,采用有限元仿真软件Abaqus对不同结构模型开展计算,分析膜片行程及应力分布,研究结构变量对膜片行程的影响。结果表明:在膜片焊接位置均存在应力集中现象,相对于无波纹及三波纹膜片,单波纹和双波纹结构较为合理;膜片厚度、波纹半径及波纹突出距离是影响膜片行程的关键因素,波纹位置对膜片行程的影响较小;针对双波纹膜片,可采用增大外侧波纹半径的结构提升膜片行程。研究结果可为小型化感温元件中膜片的结构优化设计提供理论依据。     

纤维增强复合材料波纹蒙皮基体的承载能力

本文以一种可作为变体机翼蒙皮的复合材料波纹结构为对象,研究了其横向承载能力,为其结构参数优化提供理论基础。提出了一个理论分析模型,计算了试件横向的抗弯刚度及三点弯曲载荷下的挠曲线,并计算了同等材料厚度、宽度的平板结构的抗弯刚度,比较发现,波纹结构在纵向有远大于平板结构的承载能力。模仿蒙皮实际受载情况,计算了均布载荷作用下波纹试件弯曲的挠曲线方程。制作了波纹基体承载试件及平板试件,用三点弯曲法对两种试件进行了弯曲测试,测试结果表明,在弯曲的弹性变形段内,理论计算值与测试值基本吻合,误差小于10%,证明了理论分析模型的正确性。     

槽形梁动力反应分析的能量变分法

以分析箱形梁剪滞效应提出的方法为基础,考虑了剪滞翘曲应力的自平衡条件,为了准确反应槽形梁翼板的动位移变化,三个广义动位移η(x,y,z,t)、w(x,t)和θ(x,t)被引入。利用能量变分原理建立了槽形梁动力反应w(x,t)、u(x,t)和θ(x,t)的控制微分方程和自然边界条件,获得了相应广义位移的闭合解,据此对槽形梁的动力反应特性进行了研究,揭示了槽形梁桥动力反应的规律。算例中,该解析解与有限元数值解进行了比较,证明了该动力分析方法的有效性。     

考虑自平衡条件槽形曲梁的静力学特性分析

考虑了剪滞翘曲应力自平衡条件、剪力滞后、剪切变形和翘曲扭转等因素的影响,以最小势能原理为基础,建立了薄壁槽形曲梁的弹性控制微分方程和自然边界条件,获得了弯、扭、翘和剪滞效应相耦合广义位移的闭合解。算例中,分析了不同荷载形式、曲梁半径R、宽跨比等因素对曲线槽形梁力学特性的影响。该文解析法更好揭示了曲线槽形梁的力学特性以及各参数之间的内在关系,所得公式是对曲梁剪滞理论的发展。     

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.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

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.     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

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 ...