Evaluation of Characteristics of Non-Metallic Inclusions in P/M Ni-Base Superalloy by Automatic Image Analysis

Non-metallic inclusions,especially the large ones,within P/M Ni-base superalloy have a major influence on fatigue characteristics,but are not directly measurable by routine inspection.In this paper,a method,automatic image analysis,is proposed for estimation of the content,size and amount of non-metallic inclusions in superalloy.The methodology for the practical application of this method is described and the factors affecting the precision of the estimation are discussed.In the experiment,the characteristics of the non-metallic inclusions in Ni-base P/M superalloy are analyzed.     

Processes that Promote and Deplete the Exosphere of Mercury

It has been speculated that the composition of the exosphere is related to the composition of Mercury’s crustal materials. If this relationship is true, then inferences regarding the bulk chemistry of the planet might be made from a thorough exospheric study. The most vexing of all unsolved problems is the uncertainty in the source of each component. Historically, it has been believed that H and He come primarily from the solar wind (Goldstein, B.E., et al. in J. Geophys. Res. 86:5485–5499, 1981), Na and K come from volatilized materials partitioned between Mercury’s crust and meteoritic impactors (Hunten, D.M., et al. in Mercury, pp. 562–612, 1988; Morgan, T.H., et al. in Icarus 74:156–170, 1988; Killen, R.M., et al. in Icarus 171:1–19, 2004b). The processes that eject atoms and molecules into the exosphere of Mercury are generally considered to be thermal vaporization, photon-stimulated desorption (PSD), impact vaporization, and ion sputtering. Each of these processes has its own temporal and spatial dependence. The exosphere is strongly influenced by Mercury’s highly elliptical orbit and rapid orbital speed. As a consequence the surface undergoes large fluctuations in temperature and experiences differences of insolation with longitude. Because there is no inclination of the orbital axis, there are regions at extreme northern and southern latitudes that are never exposed to direct sunlight. These cold regions may serve as traps for exospheric constituents or for material that is brought in by exogenic sources such as comets, interplanetary dust, or solar wind, etc. The source rates are dependent not only on temperature and composition of the surface, but also on such factors as porosity, mineralogy, and space weathering. They are not independent of each other. For instance, ion impact may create crystal defects which enhance diffusion of atoms through the grain, and in turn enhance the efficiency of PSD. The impact flux and the size distribution of impactors affects regolith turnover rates (gardening) and the depth dependence of vaporization rates. Gardening serves both as a sink for material and as a source for fresh material. This is extremely important in bounding the rates of the other processes. Space weathering effects, such as the creation of needle-like structures in the regolith, will limit the ejection of atoms by such processes as PSD and ion-sputtering. Therefore, the use of laboratory rates in estimates of exospheric source rates can be helpful but also are often inaccurate if not modified appropriately. Porosity effects may reduce yields by a factor of three (Cassidy, T.A., and Johnson, R.E. in Icarus 176:499–507, 2005). The loss of all atomic species from Mercury’s exosphere other than H and He must be by non-thermal escape. The relative rates of photo-ionization, loss of photo-ions to the solar wind, entrainment of ions in the magnetosphere and direct impact of photo-ions to the surface are an area of active research. These source and loss processes will be discussed in this chapter.     

应用相多普勒粒度仪研究喷雾特性

应用相多普勒粒度分析仪（ＰＤＰＡ）获得了双油路喷嘴详细的喷雾特性。将ＰＤＰＡ测得的空间点数据分别沿扫描径向和所在测量截面积分,得到液滴的线平均和面平均直径。ＰＤＰＡ的线积分数据比马尔文仪测得的线积分值要大;面积分平均直径与液膜波不稳定理论计算的初始平均直径相符合。结果表明,对描写喷雾特性和确定喷雾质量,ＰＤＰＡ是可靠的测量装置。     

颗粒增强金属基复合材料凝固过程中的颗粒推移效应

归纳了颗粒增强金属基复合材料凝固过程中颗粒推移效应的各判据,分析了各自的适用范围,提出了实际复合材料铸件中抑制颗粒推移的途径。     

Comparison of self-healing ionomer to aluminium-alloy bumpers for protecting spacecraft equipment from space debris impacts

This paper discusses the impact behavior of a self-healing ionomeric polymer and compares its protection capability against space debris impacts to that of simple aluminium-alloy bumpers. To this end, 14 impact experiments on both ionomer and Al-7075-T6 thin plates with similar surface density were made with 1.5 mm aluminium spheres at velocity between 1 and 4 km/s.     

Dynamic particle accumulation structure (PAS) in half-zone liquid bridge – Reconstruction of particle motion by 3-D PTV

Three-dimensional (3-D) velocity field reconstruction of oscillatory thermocapillary convections in a half-zone liquid bridge with a radius of O (1 mm) was carried out by applying 3-D particle tracking velocimetry (PTV). Simultaneous observation of the particles suspended in the bridge by two CCD cameras was carried out by placing a small cubic beam splitter above a transparent top rod. The reconstruction of the 3-D trajectories and the velocity fields of the particles in the several types of oscillatory-flow regimes were conducted successfully for sufficiently long period without losing particle tracking. With this application the present authors conducted a series of experiments focusing upon the collapse and re-formation process of the PAS by mechanically disturbing fully developed PAS.     

An adaptive-order particle filter for remaining useful life prediction of aviation piston pumps

An accurate estimation of the remaining useful life (RUL) not only contributes to an effective application of an aviation piston pump, but also meets the necessity of condition based maintenance (CBM). For the current RUL evaluation methods, a model-based method is inappropriate for the degradation process of an aviation piston pump due to difficulties of modeling, while a data-based method rarely presents high-accuracy prediction in a long period of time. In this work, an adaptive-order particle filter (AOPF) prognostic process is proposed aiming at improving long-term prediction accuracy of RUL by combining both kinds of methods. A dynamic model is initialized by a data-driven or empirical method. When a new observation comes, the prior state distribution is approximated by a current model. The order of the current model is updated adaptively by fusing the information of the observation. Monte Carlo simulation is employed for estimating the posterior probability density function of future states of the pump’s degradation. With updating the order number adaptively, the method presents a higher precision in contrast with those of traditional methods. In a case study, the proposed AOPF method is adopted to forecast the degradation status of an aviation piston pump with experimental return oil flow data, and the analytical results show the effectiveness of the proposed AOPF method.     

基于粒子群算法的石英挠性加速度计温度补偿方法研究

由于使用环境的需求,需要光纤惯组具有较宽的工作温度范围,一般在-40℃~60℃温度范围内有稳定且准确的输出。而实际情况下温度变化会使惯性器件输出产生温度漂移,制约惯组的输出精度。以工程实例为依托,以光纤惯组中低精度石英挠性加速度计作为研究对象,首先分析了石英加速度计的温度特性,然后设计了一种基于粒子群算法的石英加速度计温度补偿方法,并以温补后器件的零偏特性为依据,利用试验平台对温补效果进行了试验验证。试验结果表明,该温补方法能够有效补偿石英加速度计的温度漂移,补偿后的零偏稳定性较补偿前有数量级上的提升。     

Energy release in double layers

A Double layer (DL) in a current carrying plasma sustains a localised net potential difference and acts as an impedance converting electrical energy to directed particle energy determined by the DL potential. DL's accelerate equal numbers of ions and electrons for relativistic energies, otherwise electron energisation predominates. Their time independent structure may be described as a BGK (Bernstein-Greene-Kruskal) state analogous to that for laminar shocks, and certain existence criteria must be satisfied. The generalised Langmuir criterion requires total particle pressure balance over the DL and may imply propagation in the plasma reference frame. The Bohm criteria require sufficiently large current densities and are closely related to the local stability condition at the edges of the DL. The DL potential must be sustained externally, for example by the release of stored magnetic energy. A steady state is also possible where (externally maintained) mass motions drive a dynamo region connected by currents to the DL which acts as an electrical load.