挤压AZ31B镁合金多轴疲劳寿命预测

采用挤压AZ31B镁合金薄壁圆筒试样.分别进行了单轴和多轴加载下的对称应变控制疲劳实验.研究了不同加载路径对疲劳寿命的影响.单轴加载包括对称拉压和扭转路径,多轴加载包括45°比例加载和90°非比例加载路径.结果表明,在加微的等效应变幅值为0.3%—0.55%附近,4冲加载路径下的应变-寿命曲线均出现了不连续的拐点;比例加载路径在等效应变幅大于0.45%时疲劳寿命最高,拉压路径在等效应变幅小于0.45%时疲劳寿命最高;非比例加载路径的疲劳寿命最低.使用基于临界平面法的多轴疲劳模型FS,SWT以及修正SWT分别预测了各个路径加载下的疲劳寿命.预测结果表明,SWT模型对于拉压和循环扭转加载下寿命预测结果误差较大;FS模型与修正SWT模型可以较好地预测挤压AZ31B镁合金各个路径加载下的疲劳寿命.     

铸造铝合金在多轴非比例载荷下的低周疲劳行为研究

主要研究了356铸造铝合金在多轴非比例载荷下的低周疲劳性能。结果表明，合金在循环变形过程中表现为循环硬化特征，循环硬化的程度表现出对非比例加载路径的依赖性；在相同等效应变幅值下，合金的非比例加载低周疲劳寿命小于比例加载，且非比例加载低周疲劳寿命也表现出对非比例加载路径的依赖性；在多轴疲劳寿命预测模型中考虑非比例加载路径对疲劳寿命的影响可以大大提高寿命模型预测的精确度。     

不同阵列PBGA器件焊点可靠性分析

采用Anand模型描述钎料本构关系,对温度循环载荷下两种不同阵列形式的塑料球栅阵列(PBGA)Sn3.0Ag0.5Cu焊点的应力应变响应进行有限元分析.结果表明,两种不同阵列条件下,关键焊点的位置均由芯片拐角位置决定.芯片尺寸改变时,PB.GAl21焊点的最大应力值随芯片尺寸的增大而增大,但PBGA81的最大应力值随芯片尺寸增大先减小后增大.凭借Engelmaier修正的Coffin-Manson寿命预测方程,分别预测了两种不同阵列PBGA器件四种芯片尺寸条件下焊点的热疲劳寿命,结果表明芯片尺寸对焊点疲劳寿命有较大影响.     

基于多轴载荷相位差的神经网络预测钛合金疲劳寿命EI北大核心CSCD

钛合金是航空、航天等领域重要的结构材料,面临着多轴疲劳寿命预测困难与繁琐等问题。为此,本文考虑了对称正弦波加载条件下的相位差与加载路径非比例度的关系,构建一种以相位差、正应变幅值和切应变幅值作为输入变量,以疲劳寿命作为输出变量的多轴疲劳寿命预测的神经网络模型;分别以18组纯钛、14组BT9钛合金和33组TC4钛合金多轴疲劳试验数据进行训练,用另外的2组纯钛、2组BT9钛合金和5组TC4钛合金数据进行测试;最后与等效应变模型、最大切应变模型、临界面模型进行比较。结果表明:与基于实验数据的唯象预测方法相比,基于多轴载荷相位差的神经网络方法在预测钛合金疲劳寿命方面更高效、更准确、更具普适性。     

2024锻造铝合金疲劳性能研究

本文着重研究了2024锻造铝合金经过T4及T6热处理后其单轴及多轴疲劳性能。采用了两种不同热处理方式制备出具有不同微结构的2024锻造铝合金,研究其在不同加载状态下的变形行为、疲劳机制及疲劳寿命。主要内容包括：对2024锻造铝合金进行单向拉伸、应力控制的单轴拉压疲劳及两种多轴拉扭疲劳试验,研究了加载状态与疲劳寿命的关系。结果表明,2024锻造铝合金材料的疲劳寿命对热处理和加载状态的敏感性很大,表现为在相同加载状态下2024-T4和2024-T6试样的寿命差别较大,以及同一热处理试样在不同应力幅值和不同加载路径下疲劳寿命差异大。     

两级加载下两焊点拉剪点焊接头的损伤

对带有两个焊点的拉剪点焊试样进行了两级变幅疲劳加载,应力幅和平均应力均不相等.结果表明,两级变幅加载下存在应力次序效应.在低—高加载时存在"锻炼效应",线性累积损伤的值大于1;在高—低加载时存在"过载效应",高—低加载下的线性累积损伤值也大于1.在高—低加载方式下,高水平应力作用后,低水平应力剩余疲劳寿命大于按线性疲劳累积损伤法则所估算的剩余寿命,低应力作用下的剩余寿命甚至大于低应力单独作用下的全寿命.高—低加载下的线性累积损伤结果表明,焊点边缘更象是一个缺口.     

可变角度径向加载下的轴肩轴承有限元分析

以一种可变角度径向加载装置的加载轴承为对象,利用Unigraphics进行建模,再运用ANSYS Workbench软件进行仿真分析。通过仿真,模拟航空发动机轴肩轴承工作时载荷复杂多变的实际工况,同时对轴承施加多个不同方向的径向载荷,得到该轴承应力和变形的分布。结果表明:轴承的最大变形量和应力值都随着径向加载角度的增大而增大,变形的区域分布也随着角度的变化而变化,这会对轴承的疲劳寿命和失效形式产生不良的影响。仿真分析的结果为航空轴肩轴承的试验和设计提供了参考。     

温度对振动载荷下互连微焊点寿命的影响

设计了温度-定频振动两场耦合可靠性试验，应用两参数weibull统计分析和物理失效分析方法，分析了温度（25，100℃）对振动载荷下微焊点寿命的影响.结果表明，温度由25℃升高到100℃，振动载荷下的微焊点寿命显著提高，U₁位置处焊点寿命提高了106%，U₂位置处焊点寿命提高了180%；失效模式统计分析表明，随着温度的升高，焊点由界面裂纹（裂纹产生在界面处的金属间化合物与铜焊盘之间）转变为体钎料裂纹（裂纹产生在体钎料处），失效机制由脆性断裂转变为韧性断裂，失效机制的转变与焊点寿命密切相关.     

PBGA封装SAC405互连焊点热疲劳寿命预测

基于正应变对焊点疲劳寿命的影响,采用改进的Darveaux模型,通过有限元数值模拟法对PBGA封装SAC405互连焊点的热疲劳寿命进行预测。结果表明:焊点的损伤尺度沿着封装中心线增加,在芯片边界以下达到最大值,然后向着封装边界方向逐渐减小,最终在封装边界附近恢复到较大值;裂纹易在封装侧焊点和焊盘之间界面上形成,并沿着焊点圆周方向较宽的角度范围扩展,裂纹生长过程与试验结果相一致;工况2条件下的关键焊点疲劳寿命为5 525个周期,随着热循环高低温保温时间的延长,关键焊点的疲劳寿命减小。     

基于Anand模型SnAgCu-X焊点疲劳寿命预测

Anand模型采用有限元法模拟WLCSP器件Sn3.8Ag0.7Cu-X（Ce，Fe）无铅焊点在热循环载荷条件下的应力-应变响应，借助蠕变应变疲劳寿命预测模型SnAgCu，SnAgCuCe，SnAgCuFe焊点疲劳寿命.结果表明，在服役器件整体器件出现明显的变形现象，电路板翘曲严重.从中心到拐角焊点变形-应力-应变逐渐增加，芯片下拐角焊点成为整个结构潜在的危险区域.通过计算WLCSP器件SnAgCu、SnAgCuCe和SnAgCuFe三种焊点的疲劳寿命，证实了SnAgCuCe和SnAgCuFe焊点寿命明显高于SnAgCu焊点，证明了在SnAgCu中添加一定量的铈和铁可以显著提高SnAgCu焊点的使用寿命，分析结果为新型无铅钎料的研发提供理论支撑.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

Effect of Short-Time Aging on the Pitting Corrosion Behavior of a Novel Lean Duplex Stainless Steel 2002

The effect of short-time aging in the temperature range between 400 and 1000 °C on the pitting corrosion behavior and mechanical property of a novel lean duplex stainless steel(LDSS) 2002 was investigated through the potentiostatic critical pitting temperature(CPT) tests and the Charpy impact tests. Both the pitting corrosion resistance and the toughness of aged specimens degraded due to the precipitation of detrimental secondary phases and the most significant reduction of CPT and impact energy emerged at 650 °C concurrently. The CPT of LDSS 2002 specimen aged at 650 °C decreased by 28 °C, and the impact energy dropped from 69 to 29 J/cm~2 compared with the solution-annealed sample. Transmission electron microscopy characterization showed that the main precipitates in LDSS 2002 were Cr_2N and M_(23)C_6 along the ferrite–austenite grain boundaries.     

INTRODUCTION TO PATENTS

The invention provides a method of making a mold which can reduce SOx generation rate while preventing decrease in hardening rate in the case of using sulfuric acid for a hardener composition. The method has a mixture step in which fire-resistant particles, a hardener composition and a binder composition are mixed to obtain a composition for a mold. The hardener composition contains sulfuric acid. In the mixture step, sodium carbonate is added. A molar ratio of the sulfuric acid to the sodium carbonate is 0.5 or more and 4.0 or less.     

China Foundry Week 2014

China Foundry Week, hosted by the Foundry Institution of Chinese Mechanical Engineering Society （FICMES） each year, is a large academic event in China. It is one of the ten high-impact activities sponsored by the Chinese Mechanical Engineering Society.     

17th Conference of Hydrodynamic and Electromechanical Control Engineering Call for papers

正1.Contents In order to promote the academic exchanges and technical communication of the research in the field of fluid power transmission and control,fluid control engineering specialized committee of the Chinese Society of Theoretical and Applied Mechanics will hold the 17th Conference of Hydrodynamic and Electromechanical Control Engineering on July 27-29,2014 in Tibet,Lhasa city.     

Information for Contributors

正The Transactions of Nonferrous Metals Society of China,founded in 1991 and sponsored by The Nonferrous Metals Society of China,is published monthly now and mainly contains reports of original research which reflect the new progresses in the field of nonferrous metals science and technology,including mineral processing,extraction metallurgy,metallic materials and heat treatments,metal working,physical metallurgy,powder metallurgy,with the emphasis     

Preface

<正>We are pleased to present this Special Issue of Transactions of Nonferrous Metals Society of China containing selected papers from the First Asian Conference on Aluminum Alloys(ACAA-2013),held in Beijing,China,13–17 October 2013.This conference has been initiated,with approval of     

Information for Contributors

The Transactions of Nonferrous Metals Society of China, founded in 1991 and sponsored by The Nonferrous Metals Society of China, is published monthly now and mainly contains reports of original research which reflect the new progresses in the field of nonferrous metals science and technology, including mineral processing, extraction metallurgy, metallic materials and heat treatments, metal working, physical metallurgy, powder metallurgy, with the emphasis on fundamental science. It is the unique preeminent publication in English for scientists, engineers, under/post-graduates on the field of nonferrous metals industry. This journal is covered by many famous abstract/index systems and databases such as SCI Expanded, Ei Compendex Plus, 1NSPEC, CA, METADEX, AJ and JICST.     

FORMULAS OF TENSION OF CONTINUOUS ROLLING PROCESS

The development of computer controlled continuous rolling process calls for a mathematical expression that can express the inequality condition of "constant flow". Tension is the link of the continuous rolling process. From the condition of dynamic equilibrium, a differential equation of tension is given out. On the basis of the physical rules established from the industrial practice and experimental studies, the law of volume constancy, the linear relation of forward slip and tension, the state equation of continuous rolling, the formula of dynamic tension, and the formula of static tension have been obtained. These formulae reflect the functional relations between tensions, thickness, roll velocity, and time in the continuous rolling process. It is implied that the continuous rolling process is a gradually steady, controllable, and measurable dynamic system. An assumption of predicting the thickness of a steel plate using these tension formulae is also put forward.     

RHEOLOGY FEATURE OF SIMPLE METAL MELT

The rheology feature of Sb, Bi melt and alloys was studied using coaxial cylinder high-temperature viscometer. The results showed that the curve of torsion-rotational speed for Sb melt presents a linear relation in all measured temperature ranges, whereas for the Bi melt, the curve presents obvious non-Newtonian feature within the low temperature range and at relative high shear stress. The rheology feature of Sb80Bi20 and Sb20Bi80 alloy melts was well correlated with that of Sb and Bi, respectively. It is considered that the rheology behavior of Sb melt plays a crucial role in Sb80Bi20 alloy and that of Bi melt plays a crucial role in Sb20Bi80 alloy.