Mechanical wear debris feature,detection, and diagnosis: A review

Mechanical debris is an important product of friction wear, which is also a crucial approach to know the running status of a machine. Many studies have been conducted on mechanical debris in related fields such as tribology, instrument, and diagnosis. This paper presents a comprehensive review of these studies, which summarizes wear mechanisms (e.g., abrasive wear, fatigue wear, and adhesive wear) and debris features (e.g., concentration (number), size, morphology, and composition), analyzes detection methods principles (e.g., offline: spectrograph and ferrograph, and online: optical method, inductive method, resistive-capacitive method, and acoustic method), reviews developments of online inductive methods, and investigates the progress of debris-based diagnosis. Finally, several notable problems are discussed for further studies.     

MHD modeling of the outer heliosphere: Achievements and challenges

An overview is presented of magnetic-field-related effects in the solar wind (SW) interaction with the local interstellar medium (LISM) and the different theoretical approaches used in their investigation. We discuss the possibility that the interstellar magnetic field (ISMF) introduces north–south and east–west asymmetries of the heliosphere, which might explain observational data obtained by the Voyager 1 and Voyager 2 spacecraft. The SW–LISM interaction parameters that are responsible for the deflection of the interstellar neutral hydrogen flow from the direction of propagation of neutral helium in the inner heliosheath are outlined. The possibility of a strong ISMF, which increases the heliospheric asymmetry and the H–He flow deflection, is discussed. The effect of the combination of a slow-fast solar wind during solar minimum over the Sun’s 11-year activity cycle is illustrated. The consequences of a tilt between the Sun’s magnetic and rotational axes are analyzed. Band-like areas of an increased magnetic field distribution in the outer heliosheath are sought in order to discover regions of possible 2–3 kHz radio emission.     

超光滑表面杂质微粒的识别与统计技术

从理论上分析了微粒重叠对测量结果的影响,通过简化模型,给出了对粒子数测量结果的补偿曲线。并建立了分析图象分辨率、微粒识别率和识别阈值三者关系的模型,给出了在识别阈值不变情况下,图象分辨率与微粒识别率的关系图,从而可以选择优化的图象分辨率和微粒识别阈值。     

Atmospheric Ion-induced Aerosol Nucleation

Ion-induced nucleation has been suggested to be a potentially important mechanism for atmospheric aerosol formation. Ions are formed in the background atmosphere by galactic cosmic rays. A possible connection between galactic cosmic rays and cloudiness has been However, the predictions of current atmospheric nucleation models are highly uncertain because the models are usually based on the liquid drop model that estimates cluster thermodynamics based on bulk properties (e.g., liquid drop density and surface tension). Sulfuric acid (H₂SO₄) and water are assumed to be the most important nucleating agents in the free troposphere. Measurements of the molecular thermodynamics for the growth and evaporation of cluster ions containing H₂SO₄ and H₂O were performed using a temperature-controlled laminar flow reactor coupled to a linear quadrupole mass spectrometer as well as a temperature-controlled ion trap mass spectrometer. The measurements were complemented by quantum chemical calculations of the cluster ion structures. The analysis yielded a complete set of H₂SO₄ and H₂O binding thermodynamics extending from molecular cluster ions to the bulk, based on experimental thermodynamics for the small clusters. The data were incorporated into a kinetic aerosol model to yield quantitative predictions of the rate of ion-induced nucleation for atmospheric conditions. The model predicts that the negative ion-H₂SO₄-H₂O nucleation mechanism is an efficient source of new particles in the middle and upper troposphere.     

高性能铝基复合材料的颗粒分布及界面结合

采用常规粉末冶金和高能球磨粉末冶金法制备了B4Cp/Al复合材料，研究了B4C颗粒分布与界面结合特点、形成机制以及对材料性能的影响。结果表明，17％（体积分数）B4Cp/6061Al复合材料的屈服和抗拉强度分别为415MPa和470MPa，比常规粉末冶金复合材料分别提高了69％和70％。微观分析表明，高能球磨粉末冶金复合材料中B4C颗粒均匀分布、颗粒与基体之间存在近百纳米厚度的界面层，界面层由呈带状且有序分布的微细铝晶粒和弥散分布的纳米颗粒组成。高能球磨过程中，铝粉末在钢球表面形成冷焊层，B4C不断被挤入而均匀化是实现颗粒均匀分布的主要机制；球磨过程中铝粉末表面氧化层破碎暴露出新鲜铝表面且与镶嵌与铝粉末中的B4C颗粒形成界面结合是获得良好界面结合复合材料的重要条件     

3He-Rich Solar Energetic Particle Events

³He-rich solar energetic particle (SEP) events show huge enrichments of ³He and association with kilovolt electrons and Type-III radio bursts. Observations from a new generation of high resolution instruments launched on the Wind, ACE, Yohkoh, SOHO, TRACE, and RHESSI spacecraft have revealed many new properties of these events: the particle energy spectra are found to be either power-law or curved in shape, with the ³He spectrum often being distinctly different from other species. Ultra-heavy nuclei up to >200 amu are found to be routinely present at average enrichments of >200 times solar-system abundances. The high ionization states previously observed near ∼1 MeV/nucleon have been found to decrease towards normal solar coronal values in these events. The source regions have been identified for many events, and are associated with X-ray jets and EUV flares that are associated with magnetic reconnection sites near active regions. This paper reviews the current experimental picture and theoretical models, with emphasis on the new insights found in the last few years.     

韩国高性能C/C刹车盘的开发

介绍了韩国国防开发署与大宇重工合作开发的飞机C/C刹车盘的制造工艺和动力矩试验结果。韩国使用专门设计的预形体通过沥青浸渍和化学气相沉积工艺制备了具有要求的摩擦磨损性能、密度、热性能及机械性能的C/C刹车盘,在无损检测、机械加工、金属夹组装和防氧化处理等工序之后进行鉴定试验。包括动力矩试验和服役寿命试验的全部鉴定试验根据MIL—W—5013规范和洛克希德公司的GD16ZL001B规范在惯性动力仪上进行。全部鉴定试验结果显示新的刹车装置与已鉴定过的现役C/C刹车盘相比具有良好的刹车性能,达到了全部要求。     

刀具磨损对TC11铣削表面粗糙度与残余应力的影响

为了研究TC11钛合金铣削加工过程中刀具磨损对加工表面质量的影响规律,设计了刀具磨损与铣削表面粗糙度、表面残余应力的试验。结果表明:TC11钛合金铣削加工过程中的刀具磨损可以分为:初期磨损、正常磨损、剧烈磨损三个阶段。当刀具处于"初期磨损"时,TC11铣削表面粗糙度随切削时间逐渐减小,铣削表面残余应力也呈减小趋势;当刀具处于"正常磨损"阶段时,铣削表面粗糙度和铣削表面残余应力都呈增加趋势,但增加的速度平稳;当刀具进入"剧烈磨损"阶段时,铣削表面粗糙度迅速增大,表面残余应力也较前两个阶段显著增加。另外,试验过程中的TC11铣削表面残余应力均表现为压应力。     

脉冲频率对7050高强铝合金微弧氧化膜层的影响

在脉冲频率为50、250、500、750、1 000 Hz的条件下,应用微弧氧化（MAO）技术在7050高强铝合金表面制备了陶瓷膜层,并采用扫描电镜（SEM）、X射线衍射仪（XRD）、电化学工作站、摩擦磨损试验机等手段分别对陶瓷膜的表面形貌、相组成、耐腐蚀性、耐磨性等进行分析。结果表明,当脉冲频率过低时,MAO陶瓷膜层表面粗糙,影响膜层致密性;而当脉冲频率过高时,则不利于MAO陶瓷膜层生长,所得的膜层耐蚀性和耐磨性较差。当脉冲频率为250 Hz时,所制备的膜层具有最佳的耐磨性及耐蚀性。     

一种用于纳米颗粒场致发射推力器的自中和技术

纳米颗粒场致发射推力器(NFET)是一种用于微小卫星的固体工质静电推力器,为促进NFET的工程研制,提出一种新的自中和技术——反向充电中和策略。为研究这种自中和技术的设计方法,建立相应的数值模型以模拟该中和技术下羽流输运过程,并且,在真空舱中开展NFET的羽流测量试验来验证中和模型的正确性。以比色温度计和"打靶法"装置来分别测量羽流温度分布和推力,通过试验与仿真结果的对比,羽流温度变化的试验结果与仿真结果在定性规律上一致,推力的计算误差在9%～10%。在验证模型正确性的基础上,利用该数值模型对关键设计参数进行数值分析。结果表明:引出极与发射极的内径比变化会导致外加电场对剩余电荷颗粒作负功,引起推力下降,该物理参数在0.94附近时,推力达到极大值;而随着颗粒直径的增加,羽流中和区域整体向下游推移,推力升高。本文结论可为NFET的反向充电中和策略提供设计参考。