基于数字图像相关方法微裂纹萌生试验研究

为了进一步研究疲劳裂纹在萌生阶段的特点,本文结合数字图像相关方法 (Digital Image Correlation Method,DIC)设计并组建了配合液压疲劳试验机加载的原位观测系统。同时针对DIC测量方法中的关键技术进行研究,分别提出了一种可应用于视场宽度2mm下DIC计算的微小散斑制备方法,以及空间调节方法以提高试验可靠性。最后应用该系统开展针对航空发动机火焰筒材料GH536的微裂纹自然萌生试验。通过采取两种不同的DIC分析策略,分别获得疲劳过程中的总应变幅以及最大累积塑性应变的演化规律。结果表明总应变幅演化可确定自然萌生裂纹位置,最小可识别50μm裂纹;最大累积塑性应变分析可得萌生寿命占比约85%,并在裂纹出现后塑性应变急剧增加。     

Statistical description of low-latitude plasma blobs as observed by DMSP F15 and KOMPSAT-1

The global distribution of low-latitude plasma blobs was investigated by in-situ plasma density measurements from the Korea Multi-Purpose Satellite-1 (KOMPSAT-1) and Defense Meteorological Satellite Program (DMSP) F15. In the observations, blobs occurred in the longitude sector where the activity of the equatorial plasma bubble (EPB) was appreciable, and additional blobs were found at the lower (KOMPSAT-1) altitude as in the EPBs. However, several notable differences exist between the distributions of EPBs and blobs. First, KOMPSAT-1 found few blobs around 0°E in March and June, as did DMSP F15 from 30°W to 120°E for every season. Second, the overall occurrences in December and March at the DMSP F15 (840 km) altitude were somewhat lower than expected from those of the EBPs. Third, at the DMSP F15 altitude, the occurrence probability of plasma blobs was less controlled by yearly variations in the solar activity. These results imply that topside ionospheric conditions as well as the existence of EPBs control further development of blobs. Additionally, it was found that the blob latitudes became higher as the yearly solar activity increased. Moreover, most of the blobs were encountered in the winter hemisphere, possibly due to the low ambient density.     

十九样片太阳吸收率原位测试的自动控制

文章介绍了利用 Genie 及 Visual Basic 编写的19样片太阳吸收率原位测试自动控制程序,实现了19样片太阳吸收率原位测试过程的自动控制.     

原位自生MAX 相增强TiAl 基复合材料

叙述了近年来国内外原位自生MAX相增强TiAl基复合材料的研究进展。叙述了MAX相结构和性能,MAX相增强TiAl基复合材料的原位合成工艺的研究进展及原位合成机理,并对复合材料的微观组织、界面结构以及力学性能进行了综述,最后对其应用进行展望。     

Analytical model of cutting force in axial ultrasonic vibration-assisted milling in-situ TiB2/7050Al PRMMCs

Ultrasonic vibration-assisted milling has been widely applied in machining the difficult-to-cut materials owing to the remarkable improvements in reducing the cutting force. However, analytical models to reveal the mechanism and predict the cutting force of ultrasonic vibration-assisted milling metal matrix composites are still needed to be developed. In this paper, an analytical model of cutting force was established for ultrasonic vibration-assisted milling in-situ TiB₂/7050Al metal matrix composites. During modeling, change of motion of the cutting tool, contact of tool-chip-workpiece and acceleration of the chip caused by ultrasonic vibration was considered based on equivalent oblique cutting model. Meanwhile, material properties, tool geometry, cutting parameters and vibration parameters were taken into consideration. Furthermore, the developed analytical force model was validated with and without ultrasonic vibration milling experiments on in-situ TiB₂/7050Al metal matrix composites. The predicted cutting forces show to be consistent well with the measured cutting forces. Besides, the relative error of instantaneous maximum forces between the predicted and measured data is from 0.4% to 15.1%. The analytical model is significant for cutting force prediction not only in ultrasonic-vibration assisted milling but also in conventional milling in-situ TiB₂/7050Al metal matrix composites, which was proved with general applicability.     

基于考虑时间效应UH模型的一维固结分析

结合考虑时间效应的统一硬化(UH)模型得到一维固结下土的一维应力-应变关系,以此建立一维固结控制微分方程,可以统一考虑土的主、次固结变形.采用差分方法对单面排水固结问题进行了分析,加载初期不透水层处存在有效应力减小的松弛现象,推导了不透水层处有效应力随时间减小的公式并进行分析.随后,采用数值方法分析了次固结系数、超固结度、压缩回弹系数等因素对固结的影响规律,分析结果也验证了所得公式的结论.此外,通过室内试验对控制方程预测规律进行了验证分析.当主固结基本完成后,变形主要由次固结产生,基于这个条件推导了平均固结度与时间的关系,该公式可以用于计算固结基本完成需要的时间.      

嫦娥三号月面巡视器机械臂就位探测规划

提出了一种基于SA *算法的嫦娥三号月面巡视器机械臂就位探测规划方法。建立了机械臂的正逆运动学模型,满足机械臂与环境不存在干涉的约束条件,并通过碰撞检测避免机械臂与环境和巡视器本体发生干涉;利用SA *算法在机械臂的工作空间进行搜索,在机械臂位形切换次数最少的优化条件下,实现了月面巡视器机械臂就位探测规划;通过月面巡视器在轨任务执行数据验证了基于SA *算法的月面巡视器机械臂就位探测任务的可行性。     

Prediction of ionospheric total electron content using adaptive neural network with in-situ learning algorithm

The Ionospheric Total Electron Content is responsible for the group delay of the signals from the Navigation satellites. This delay causes ranging error, which in turn degrades the accuracy of position estimated by the receivers. For critical applications, single frequency receivers resort to Satellite Based Augmentation Systems in order to have improved accuracy and integrity. The performance of these systems in terms of accuracy can be improved if predictions of the delays are available simultaneously with real measurements. This paper attempts to predict the Total Electron Content using adaptive recurrent Neural Network at three different locations of India. These locations are selected at the magnetic equator, at the equatorial anomaly crest and outside the anomaly range, respectively. In-situ Learning Algorithm has been used for tracking the non-stationary nature of the variation. Prediction is done for different prediction intervals. It is observed that, for each case, the mean and root mean square values of prediction errors remain small enough for all practical applications. Analysis of Variance is also done on the results.     

舵面展开机构模拟系统校准方法研究CSCD

通过对舵面展开机构模拟系统的原理分析,提出了原位校准方法,介绍了现场模拟系统的校准方法,解决了专用测试设备无法校准的问题,对于今后指导专用测试设备的校准起到了很好的指导意义。通过对扭矩的试验结果分析了测量不确定度的来源、评定方法和评定过程。