7075铝合金冷搓成形本构关系及有限元分析应用研究

目的 研究7075铝合金在高应变速率下的本构关系,并将其应用于有限元仿真分析中,以实现对7075铝合金环槽铆钉冷搓成形过程的精确预测。方法 利用霍普金森压杆(SHPB)实验获得7075铝合金在1 000~4 500 s⁻¹应变速率下的真实应力-应变曲线。结合静态压缩实验在0.001 s⁻¹应变速率下的结果构建了优化的Johnson-Cook(J-C)本构模型,并应用有限元仿真对7075铝合金环槽铆钉冷搓成形过程进行模拟预测。结果 当应变速率由0.001 s⁻¹上升至3 000 s⁻¹时,7075铝合金的屈服强度增长较少,但当应变速率由3 000 s⁻¹上升至4 500 s⁻¹时,屈服强度提高了45 MPa。利用优化的J-C本构模型对真实应力进行预测,其平均相对误差与相关系数分别为0.35%和0.999 2。有限元分析结果显示,在成形过程中,铆钉零件任意部位的最大应变速率基本低于4 500 s⁻¹。外形预测结果与实际测量值的最大绝对误差为0.08 mm,最大相对误差为3.45%。结论 当应变速率由3 000 s⁻¹上升至4 500 s⁻¹时,7075铝合金展现出了明显的应变率强化效应,优化的J-C本构模型能够准确预测7075铝合金在0.001 ~4 500 s⁻¹应变速率范围内的真实应力。将其应用于有限元分析能够准确预测7075铝合金环槽铆钉冷搓成形过程。     

电子束精炼GH4068高温合金的除杂工艺及机制研究

目的 探究电子束精炼法对GH4068合金中夹杂物去除行为的影响。方法 用电子束熔炼设备对常规冶炼法制备的GH4068高温合金进行了精炼,使用扫描电子显微镜(SEM)及其配备的能谱(EDS)功能探究了合金中夹杂物的形貌、成分、数量及尺寸,并用AZtec软件进行了统计分析。结果 在GH4068合金中,含量最多的夹杂物为Al2O3-TiN复合型夹杂物,其次为氧化物、氮化物以及少量的碳氮化物。经电子束精炼后,合金中的O含量、N含量、夹杂物的数量密度和面积密度以及最大夹杂物尺寸均有所降低;当精炼参数为12 kW-30 min时,精炼效果最佳,合金中的氧的质量分数降低到6.50×10⁻⁶(下降了80.06%),氮的质量分数降低到0.13×10⁻⁶(下降了95.00%),夹杂物的数量密度和面积密度分别降低到21.99个/mm²和34.08 μm²/mm²(分别降低了45.62%和52.40%),最大夹杂物面积降低到12.59 μm²(母材面积为50.23 μm²),GH4068的纯净度得到了显著提高。结论 电子束精炼法有良好的除杂效果,且除杂效果随功率的升高呈现出先增强后减弱的趋势,GH4068合金的最佳精炼工艺参数为12 kW-30 min。     

冷拔态GH4738合金热变形本构方程及热加工图

目的 研究紧固件用冷拔态GH4738合金棒材在不同工艺参数下的热变形行为,为紧固件热加工工艺参数优化提供理论指导。方法 采用Gleeble-3500热模拟实验机对冷拔态GH4738合金棒材在变形温度1 000~1 080 ℃、应变速率1~10 s⁻¹条件下进行了热压缩实验,变形量为50%。计算了该合金的材料常数和变形激活能Q,建立了基于峰值应力的冷拔态GH4738合金的本构方程,根据动态材料模型理论绘制了冷拔态GH4738合金的能量耗散图和失稳图,获得了合金在不同应变下的热加工图,并讨论了显微组织演变情况。结果 冷拔态GH4738合金的流变应力随着变形温度的增加或应变速率的减小而降低。线性回归的相关系数证实了描述该材料热变形行为的本构方程的准确性。基于冷拔态GH4738合金的热加工图及显微组织验证结果可得,冷拔态GH4738合金的主要失稳区工艺参数区间为1 000~1 035℃/0.12~3 s⁻¹,1 030~1 072℃/ 0.25~10 s⁻¹和1 075~1 080 ℃/2.72~10 s⁻¹。热加工较佳工艺条件为1 000~1 028 ℃/0.02~0.14 s⁻¹和1 040~1 080 ℃/ 0.06~0.74 s⁻¹。结论 通过对冷拔态GH4738合金热变形本构方程和热加工图进行研究,获得了冷拔态GH4738合金优化的热变形工艺参数,可用于指导冷拔态GH4738合金的紧固件热加工成形。     

用于原子重力仪的扫频频率源系统

原子重力测量实验中,需要通过扫频频率源来实现主从Raman激光的线性啁啾,进而补偿原子在自由下落过程中产生的多普勒频移,实现当地重力加速度g的测量。针对传统扫频频率源体积大、发热量大的问题,通过AD9959数字芯片设计了一款扫频频率源,可用作原子喷泉扫频控制和Raman光锁相环鉴频鉴相本振参考。最终通过实验测得：该扫频信号源的相位噪声为-112 dB@1 kHz,频率稳定度为1.38×10^-11@1 s,对原子重力仪灵敏度影响为2.81×10^-9 g/Hz^1/2,600 s积分时间对原子重力仪实验影响为1.15×10^-10 g。该系统具有低噪声、高稳定度的特点,可满足搬运式原子重力仪分辨力10^-10 g需求。研究结果为原子重力仪从原理样机向工程化可搬运实验测试仪器发展提供了一定参考。     

退火温度对大塑性变形Al-8Mg纳米晶铝合金微观结构与性能的影响

目的 研究不同退火温度下高压扭转Al-8.0Mg铝合金的微观结构及其对热稳定性的影响。方法 利用X射线衍射定量计算了纳米晶Al-8Mg合金在不同退火温度下的微观结构参数。通过透射电子显微镜观察了不同状态的微观结构,讨论了晶粒尺寸和位错密度对热稳定性的影响,并分析了高温下析出相和孪晶的结构演变。结果 随着退火温度从125 ℃上升至280 ℃,HPT后Al-8.0Mg铝合金的显微硬度由247HV减小至144HV,240 ℃为硬度转变的临界温度,当退火温度低于240 ℃时,试样硬度值降低幅度较小。平均晶粒尺寸从125 ℃下的41.1 nm增大到280 ℃下的143.6 nm,位错密度由1.32×10¹⁵ m⁻²减小到3.54×10¹² m⁻²。结论 在退火温度低于240 ℃时,合金表现出较好的热稳定性,在280 ℃以后析出了大量Al3Mg2相,并观察到了多重退火孪晶。额外的能量在位错结构的回复和非平衡晶界的重排过程中被消耗,导致晶粒尺寸与显微硬度没有发生明显变化。加热过程中产生的结构转变可能是提高材料热稳定性的主要原因。     

2195铝锂合金热变形流变行为与热加工图研究

目的 研究2195铝锂合金在实验温度360~510 ℃、应变速率0.01~10 s⁻¹条件下的热压缩变形行为,建立其本构模型及热加工图,获取该合金的安全加工工艺参数。方法 采用Gleeble−3500热模拟试验机进行热变形实验,分析合金的流变行为及热加工图,结合微观组织阐述其热变形机理,并对所得最优参数进行热挤压实验验证。结果 2195铝锂合金的流变应力随变形温度增加而减小,随应变速率增加而增加;其热激活能Q为203.643 9 kJ/mol、结构因子A为1.943 9×10¹⁴、应力因子α为0.013、应变硬化指数n为5.883 9。确定合金的主要失稳区工艺参数区间为379~420 ℃、0.75~10 s^–1和480~510 ℃、1～10 s⁻¹,安全加工区间为440~510 ℃、0.01~0.25 s⁻¹。铸态2195铝锂合金的屈服和抗拉强度分别仅为(179±6)MPa和(239±11)MPa,经热挤压实验后分别达到(605±6)、(633±3)MPa,分别提高了3.5和2.6倍;铸态合金的显微硬度仅为(115±1)HV,热加工后型材达到(178±4)HV,相较于铸态合金增加了54%。结论 2195铝锂合金的流变行为符合正应变速率敏感特征,其安全加工区域集中在高温低应变速率区,主要发生了动态再结晶,实验型材在此区域表现出卓越的力学性能。     

Multiple implantation of29Si+ in semi-insulating GaAs and its characterisation

Formation of a uniformn-layer by multiple²⁹Si⁺ implantation on LEC grown semi-insulating GaAs 〈100〉 substrate and its characterisation by differential Hall measurement at room temperature is reported. The implantation energies are 60, 160 and 260 keV with corresponding doses of 1 × 10¹², 2·55 × 10¹² and 3 × 10¹² cm⁻². Asimplanted, uncapped substrates were furnace-annealed with face-to-face configuration in an N₂ ambient at 850°C with arsenic overpressure. After annealing, the samples were subjected to Hall measurements using Van der Pauw configuration. Experimental and theoretical (LSS) profiles are compared. Electrical activation of the dopant atoms was found to range from 65–90% with average mobility values lying between 2000–2300 cm² V⁻¹ s⁻¹. Uniform concentration of then-layer ∼ 10¹⁷ cm⁻³ up to a depth of 0·3 μm has been achieved. These layers are used for the fabrication of power MESFETs.     

纳米多晶Mg-Y合金压缩力学行为的分子动力学研究

目的 研究纳米多晶Mg-Y合金在不同温度和应变速率下的力学响应以及不同变形条件下的晶粒变形行为。方法 通过ATOMSK软件构建了晶粒取向随机的纳米多晶Mg-Y二元合金模型,利用LAMMPS软件,在400~520 K温度及1×10¹⁰ s⁻¹、1×10⁹ s⁻¹应变速率下完成了纳米多晶Mg-Y合金的压缩模拟,借助后处理OVITO软件对模拟结果进行了分析。结果 随着温度的升高,纳米多晶Mg-Y合金的力学性能降低,且在温度上升到一定程度后具有一定的梯度规律。在微观层面,温度的上升使总体位错密度下降,但减少了晶粒内部的长程位错和位错扭结,并且<c+a>类位错与<a>类位错的比例上升。纳米多晶Mg-Y合金在高应变速率下的屈服强度更高,在原子排布层面上,六方最密堆积的比例降低。结论 温度升高带来的更多能量使低能态的Y原子更容易参与到位错产生、消失过程中,还加剧了<c+a>类型位错向<a>类位错的转变。高应变速率通过大幅度转化基体Mg的六方最密堆积形式,增加了晶界的破碎和形核,影响了合金的力学性能。     

Ti-Al-Nb合金的热变形与动态再结晶行为研究

目的 建立本构方程及动态再结晶模型,描述热变形条件对Ti-Al-Nb合金动态再结晶以及合金软化的影响规律。方法 基于热模拟压缩变形试验,获得Ti-Al-Nb系合金在不同热变形工艺参数下的应力应变曲线。采用双曲正弦模型表征流动应力,通过线性回归等数据处理方式求得各参数的具体数值。结果 求得动态再结晶活化能Q=197.626 kJ/mol,材料常数A的平均值为3.173×10⁶,建立流动应力本构方程。Z/A为无量纲参数,通过最小二乘线性拟合求得ε^*=344×10⁵(Z/A)^0.495,εc=16.15(Z/A)^0.24。结论 Ti-Al-Nb系合金在峰值应力出现之前均发生了动态再结晶:当应变速率较高时,在流动稳定前会发生强烈的软化,曲线显现双峰;当应变速率较低时,在加工硬化和软化作用达到平衡后逐渐进入稳定阶段,此时曲线显现单峰。研究结果将为Ti-Al-Nb系合金的精密塑性成形提供一定的技术参考和理论依据。     

磁脉冲点焊焊枪的设计及仿真分析

目的 根据现有平板线圈的不足,设计了一种用于自动化作业的磁脉冲点焊焊枪。方法 采用有限元模拟方法对比分析了磁脉冲点焊焊枪线圈和现有平板线圈的性能差异,并对磁脉冲点焊焊枪线圈的结构进行了优化。结果 当线圈工作部分高10 mm、宽4 mm时,焊枪线圈和平板线圈的最大电流密度、最大磁感应强度、最大洛伦兹力分别为3.142×10¹⁰A/m²和3.639×10¹⁰A/m²、19.40 T和21.69 T、5.149×10¹¹ N和1.626×10¹² N。当线圈工作部分宽4 mm时,随着高度由10 mm降低至4 mm,焊枪线圈的最大电流密度和最大洛伦兹力分别提升了27.56%和57.64%。当驱动能力接近时,焊枪线圈所产生的位移仅为平板线圈的13.09%。当焊枪线圈工作部分截面为10 mm×10 mm的方形时,飞板凸台在20 μs时的速度仅为200 m/s;而当截面为ϕ5.6 mm的圆形时,飞板凸台在19.2 μs时便产生237 m/s的速度。结论 在工作部分的高度和宽度相同的情况下,焊枪线圈的性能要弱于现有平板线圈的性能。在宽度不变的条件下降低焊枪线圈工作部分的高度可以增大飞板的电流密度、洛伦兹力和速度,并且在性能相近的情况下,焊枪线圈工作部分所受应力要小于现有平板线圈所受应力。另外,将磁脉冲点焊焊枪线圈工作部分的截面由方形替换为相同面积的圆形,可以获得更优的焊接条件。     

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.……     

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...     

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.……     

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.     

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.     

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