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Ovidiu Maris Georgeta Maris 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(12):2129-2140
The high-speed plasma streams in the solar wind are investigated during the solar cycles nos. 20–22 (1964–1996), separately on the two types of streams according to their solar origin: the HSPS produced by coronal holes (co-rotating) and the flare-generated, in keeping with the classification made in different catalogues. The analysis is performed taking into account the following high-speed stream parameters: the durations (in days), the maximum velocities, the velocity gradients and, the importance of the streams. The time variation of these parameters and the high-speed plasma streams occurrence rate show an 11-year periodicity with some differences between the solar cycles considered. A detailed analysis of the high-speed stream 11-year cycles is made by comparison with the “standard” cycles of the sunspot relative number (Wolf number). The different behaviour of the high-speed stream parameters between even and odd solar cycles could be due to the 22-year solar magnetic cycle. The increased activity of the high-speed plasma streams on the descendant phases of the cycles, regardless of their solar sources, proves the existence of some special local conditions of the solar plasma and the magnetic field on a large scale that allow the ejection of the high energy plasma streams. This fact has led us to the analysis the stream parameters during the different phases of the solar cycles (minimum, ascendant, maximum and, descendant) as well as during the polar magnetic field reversal intervals. The differences between the phases considered are pointed out. The solar cycles 20 and 22 reveal very similar dynamics of the flare-generated and also co-rotating stream parameters during the maximum, descendant and reversal intervals. This fact could be due to their position in a Hale Cycle (the first component of the 22-year solar magnetic cycle). The 21st solar cycle dominance of all co-rotating stream parameters against the 20th and 22nd solar cycle ones, during almost all phases, could be due to the same structure of a Hale Cycle – solar cycle 21 is the second component in a 22-year SC. During the reversal intervals, all high-speed stream parameters have comparable values with the ones of the maximum phases of the cycles even if this interval contains a small part of the descendant branch (solar cycles 20 and 22). 相似文献
125.
针对相对疏松的铸造钛合金和相对密实的锻造钛合金的焊接问题,开展了两种状态的TC4钛合金电子束焊接工艺研究,对比了不同焊接参数对焊接质量的影响。研究结果表明,采用方波扫描可以较好地实现铸造钛合金与锻造钛合金的连接,焊缝成形良好,内部无缺陷;焊接接头力学性能分析表明,拉伸断裂位置全部在铸件母材区一侧。实焊结果证明,电子束焊接可以实现异种状态TC4钛合金焊接的工程化应用。 相似文献
126.
The Forming Limit Curve (FLC) of the third generation aluminum-lithium (Al-Li) alloy 2198-T3 is measured by conducting a hemispherical dome test with specimens of different widths. The theoretical prediction of the FLC of 2198-T3 is based on the M-K theory utilizing respectively the von Mises, Hill'48, Hosford and Barlat 89 yield functions, and the different predicted curves due to different yield functions are compared with the experimentally measured FLC of 2198-T3. The results show that though there are differences among the four predicted curves, yet they all agree well with the experimentally measured curve. In the area near the planar strain state, the predicted curves and experimentally measured curve are very close. The predicted curve based on the Hosford yield function is more accurate under the tension-compression strain states described in the left part of the FLC, while the accuracy is better for the predicted curve based on Hill'48 yield function under the tension-tension strain states shown in the right part. 相似文献
127.
The Forming Limit Curve (FLC) of the third generation aluminum-lithium (Al-Li) alloy 2198-T3 is measured by conducting a hemispherical dome test with specimens of different widths. The theoretical pred... 相似文献
128.
选取TC4 钛合金四层板加强结构中双层板为研究对象,采用激光穿透焊接工艺代替传统超塑成
形/ 扩散连接(SPF/ DB)工艺中涂止焊剂连接。借助ABAQUS 有限元分析软件对超塑成形过程进行分析,得到
优化的压力-时间(p-t)曲线,作为双层板超塑成形过程的气压加载曲线,进行实验验证。结果表明:成形后零
件壁厚分布均匀,焊缝处无撕裂现象,与有限元模拟结果保持一致;用此新工艺代替传统SPF/ DB 工艺中的止
焊剂具有可行性。
相似文献
129.
Unlike monocrystalline cubic boron nitride (CBN), polycrystalline CBN (PCBN) shows not only higher fracture resistance induced by tool-workpiece interaction but also better self-sharpening capability; therefore, efforts have been devoted to the study of PCBN applications in manufacturing engineering. Most of the studies, however, remain qualitative due to difficulties in experimental observations and theoretical modeling and provide limited in-depth understanding of the self-sharpening behavior/mechanism. To fill this research gap, the present study investigates the self-sharpening process of PCBN abrasives in grinding and analyzes the macro-scale fracture behavior and highly localized micro-scale crack propagation in detail. The widely employed finite element (FE) method, together with the classic Voronoi diagram and cohesive element technique, is used considering the pronounced success of FE applications in polycrystalline material modeling. Grinding trials with careful observation of the PCBN abrasive morphologies are performed to validate the proposed method. The self-sharpening details, including fracture morphology, grinding force, strain energy, and damage dissipation energy, are studied. The effects of maximum grain cut depths (MGCDs) and grinding speeds on the PCBN fracture behavior are discussed, and their optimum ranges for preferable PCBN self-sharpening performance are suggested. 相似文献
130.
This paper seeks to mark the fruitful collaborative research between scholars in the University of Southampton and Beihang University for last 25 years on structural integrity. Their efforts addressed some important issues in structural integrity such as fatigue and fracture behavior,fatigue load spectra, fatigue and fracture lifetimes, reliability-based service period, adhesively bonded composite patch repairs, Plain Woven Fabric(PWF) composites and composite artefacts.New advances in engineering approaches, experimental methods, numerical algorithms and understanding of failure mechanisms relating to structural integrity are highlighted. Probable limits(or drawbacks) are also discussed. This review provides an insight into the general aspects on structural integrity and constitutes a basis for pointers to the further works on structural integrity. 相似文献