钛/钢爆炸焊接界面波形及缺陷组织的形成机理

为探讨钛/钢爆炸焊接界面波形的形成过程和缺陷组织的形成机理,以台阶型基板爆炸焊接装置为例,选取厚度为2 mm的钛板和钢板以5、7、9、11 mm为间距进行爆炸焊接实验,并采用Autodyn动力学软件进行仿真模拟。将采用的光滑粒子动力学(SPH)数值模拟结果与实验结果作对比,观察焊接界面电镜扫描(SEM)图片中的旋涡状结晶熔池和碰撞粒子的速度矢量图。研究表明:光滑粒子动力学数值模拟方法适用于模拟爆炸焊接等金属碰撞接触的大变形行为;爆炸焊接实验中出现的界面波形的形成原因可用碰撞局部金属流体的相互侵彻理论来解释;基板和复板碰撞处的金属涡流是焊接界面形成缺陷组织的主要原因。     

SPH方法在圆柱型装药与钢板接触爆炸分析中的应用

基于显式动力分析软件LS-DYNA,利用SPH方法对圆柱型装药爆轰问题进行了数值模拟,计算结果表明SPH方法可以准确模拟炸药爆轰及产物膨胀飞散过程。在此基础上建立了圆柱型装药与钢板接触爆炸的三维数值计算模型,分析了接触爆炸荷载作用下钢板的动力响应问题,模拟结果直观显示了接触爆炸作用下钢板发生层裂和穿孔破坏的过程;进行了等比例圆柱型装药与钢板接触爆炸试验,数值计算结果与试验结果符合较好,说明SPH方法可以准确描述爆炸作用下结构的动力响应。     

考虑空化效应的舰艇水下爆炸仿真研究

为了分析空化效应对舰艇水下爆炸冲击响应的影响。对一维Bleich—Sandler模型进行了数值仿真计算,验证了计算方法的正确性,分析了空化闭合二次加载产生的速度截断现象,并应用于二维中截面舰艇模型水下爆炸数值仿真。结果表明空化在冲击波到达结构表面后就会发生,空化闭合会产生显著的二次冲击加载作用。这在舰艇水下爆炸仿真计算中必须加以考虑。     

基复板间距对爆炸焊接质量影响的数值模拟

为了研究间距对爆炸焊接质量的影响,选取厚度为2 mm的钛板和钢板以2.5、4.5、6.5、8.5、10.5 mm为间距,借助有限元软件LS-DYNA,采用SPH-FEM耦合的方法,对爆炸复合过程做了三维数值模拟。结合材料参数计算并建立了爆炸复合窗口。模拟结果显示:随着基复板间距的增大,焊接界面结合强度呈由低到高、由高到低的变化过程,与实验结果相吻合。当间距为6.5 mm时,碰撞速度的模拟结果接近爆炸复合窗口内的最大值,表明此时结合质量较好,模拟结果与实验吻合较好。借助SPH法得到了复合板结合面的界面形貌,模拟结果与实验的金相结果一致性较好,模拟结果显示在间距为6.5～8.5 mm之间时,能够得到较好的爆炸焊接界面波形。     

1060Al/SS304板材铝箔气化焊接界面形成过程数值模拟

目的 对1060Al/SS304板材铝箔气化焊接过程进行数值模拟,揭示焊接界面的形成与演变规律.方法 基于非线性有限元软件LS-DYNA,建立1060Al/SS304板材铝箔气化焊接过程的光滑粒子流体动力学(SPH)模型,分析冲击速度对焊接界面形貌的影响,对界面形貌进行实验对比分析.结果 研究结果显示1060Al/SS...     

应用SPH方法模拟近水面爆炸

应用无网格光滑粒子法对近水面爆炸问题进行了数值模拟,模拟再现爆轰产物、水以及空气多种介质间的相互作用过程。相对于传统的基于网格的数值方法,SPH方法的无网格、Lagrangian性质能够自然、简单地处理爆炸产生的大变形、多介质作用等问题。通过自编程序,选用有效合理的SPH理论方法再现了近水面爆炸的复杂物理现象,定性分析了近水面爆炸的密度和压强的分布情况。通过数值模拟,近水面爆炸的复杂物理现象得到了合理再现,同时验证说明了光滑粒子法能有效地对可压缩多介质流进行计算模拟。     

基于SPH方法的柱状装药爆炸扩腔数值模拟

在LS-DYNA框架内建立基于SPH方法的柱状装药爆炸扩腔数值模型,克服有限元法或有限差分法在处理爆炸近区大变形和不连续问题的弊端,模拟了柱状装药起爆时岩石内部爆腔的形成过程,并对内部质点的压力和位移变化规律进行分析。结果表明:SPH方法能够较好地模拟柱状装药爆炸时岩石爆腔的形成过程,在处理爆炸近区具有一定优越性。柱状装药反向起爆后,在岩石中引起强烈的爆炸应力波,应力波波阵面近似成椭圆形;炸药底部的3个SPH粒子压力在短时间内达到峰值,然后逐渐振荡衰减;爆炸扩腔完成时间大约是500μs,爆腔呈椭球形,直径大约是16cm。     

基于SPH方法的柱状装药爆炸扩腔数值模拟

在LS-DYNA框架内建立基于SPH方法的柱状装药爆炸扩腔数值模型,克服有限元法或有限差分法在处理爆炸近区大变形和不连续问题的弊端,模拟了柱状装药起爆时岩石内部爆腔的形成过程,并对内部质点的压力和位移变化规律进行分析。结果表明:SPH方法能够较好地模拟柱状装药爆炸时岩石爆腔的形成过程,在处理爆炸近区具有一定优越性。柱状装药反向起爆后,在岩石中引起强烈的爆炸应力波,应力波波阵面近似成椭圆形;炸药底部的3个SPH粒子压力在短时间内达到峰值,然后逐渐振荡衰减;爆炸扩腔完成时间大约是500μs,爆腔呈椭球形,直径大约是16cm。     

冷爆炸压实中纳米陶瓷粉末摩擦传热研究

对纳米陶瓷颗粒在爆炸冲击波作用下的受力特点进行了分析,利用准静态弹性力学方法研究了颗粒间的冲击摩擦力大小,并利用热传导的尺寸效应和冲击摩擦的强瞬态性(忽略传热的边界散射影响),研究了摩擦引起的颗粒内部温度变化和温度场分布.ITO纳米陶瓷粉末参数的计算分析表明,冷爆炸压实中纳米陶瓷粉末颗粒间很难形成摩擦焊接.要提高纳米陶瓷粉末爆炸压实后的结合强度,必须加强陶瓷颗粒在压实过程中的烧结行为,建议在纳米陶瓷粉末的爆炸压实中采取预热爆炸压实的工艺路线.     

基于SPH方法的低韦伯数下三维液滴碰撞聚合与反弹数值模拟研究

光滑粒子流体动力学方法（SPH方法）作为纯拉格朗日粒子方法,可以有效避免网格法在模拟大变形过程中带来的网格扭曲等缺陷,适合模拟含大变形的液滴碰撞聚合与反弹过程。该文基于Ott和Schnetter提出的修正SPH方法,利用有限差分与SPH一阶导数相结合的方法处理粘性项中的二阶导数问题,进行Couette流算例验证,数值解...     

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.……     

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...     

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.     

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.     

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 ...