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《Materials Science & Technology》2013,29(11):1367-1374
AbstractThe isothermal constant stress creep tests data for a 9Cr–1Mo–0·2V (P91 type) steel were submitted for a phenomenological analysis in order to obtain the relevant creep equation for such steel. Namely, the minimum creep strain rate of P91 type steel cannot be described by the simple Arrhenius type power law constitutive model. The incorporation of the threshold stress concept in the analysis of creep data leads to a modified power law, which satisfactorily describes the creep behaviour of the examined P91 steel. However, the threshold stress is not a good material parameter, as it often varies with temperature and/or applied stress. This adds uncertainty to the extrapolation of the creep rates into ranges where experimental data are not available. Besides the fact that the physical foundation for a threshold stress is questionable from a scientific point of view, this is a serious practical limitation of the modified power law creep equation. The second creep equation proposed in the present paper is the improved stress dependent energy barrier model. The improvement of the standard model is based on two assumptions: first, on the hypothesis that the application of a stress also affects the energy barrier to be overcome when a local region transitions from the initial to the final state, and second, by applying a simple power function of stress instead of a hyperbolic sin function in the model based equation. The obtained value of stress exponent, n=5·5, is too high for entirely climb controlled creep. The apparent activation energy of approximately 510 to 545 kJ mol?1, which is considerably higher than the activation energy for lattice diffusion, is the stress dependent activation energy of the slowest, dominant rate controlling process of the supposed multiple creep mechanisms. 相似文献
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《Advanced Robotics》2013,27(1):49-69
The purpose of this study is to develop a virtual wall display system for a walk simulator to grope its way in an 'invisible' situation, such as in a building filled with dense smoke, etc. To reproduce the realistic haptic sense of a building wall, the implementation of the wideness and the rigidity of wall are essential. Wideness of a virtual wall was realized by a hand-tracking control combined with a small wall panel which is mounted on a three-axis Cartesian manipulator. A 6-d.o.f. magnetic tracking system was utilized for the hand position tracking in the non-contact situation of the hand and the panel. In the contact situation, high rigidity of the wall was attained as stiffness in the normal direction is provided to the wall panel to represent the haptic sense of a rigid wall. Force-based tracking provides the low stiffness in the tangential direction to make the wall panel move easily along the direction of hand movement to represent a wide plain wall. A three-axis force sensor is attached on the wall panel to detect the contact force. The realization of smooth switching between both tracking controls provides the user with the haptic feel of the presence and continuity of a virtual wall. In addition, the frictional sensation has the effect of giving the system more reality. Experimental results have shown the effectiveness of the hybrid tracking method for the virtual wall system. 相似文献
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《International Journal of Cast Metals Research》2013,26(3):164-172
AbstractHypoeutectic 16%Cr cast irons, both Mo free and 1–3%Mo containing specimens were prepared to investigate their abrasion wear behaviour. Annealed specimens were hardened at 1323 K and then tempered at three temperatures from 673 to 873 K for 7·2 ks, the temperature giving the maximum hardness (HTmax) and the lower and higher temperature, (L-HTmax, H-HTmax). The abrasion wear behaviour was investigated using a two body type Suga abrasion wear tester. A linear relation was obtained between wear loss and wear distance. The highest wear resistance or the lowest wear rate (R W) was obtained in H Tmax specimens except for the Mo free specimen. The lowest wear resistance or the highest R W was obtained in H-HTmax specimens. The R W was decreased with an increase in macrohardness. The lowest R W appeared around 25% retained austenite (V γ ). The R W was decreased with an increase of Mo content, and the V γ value at the minimum R W shifted to the high V γ side. 相似文献
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《Science & Technology of Welding & Joining》2013,18(3):267-271
AbstractAn autogenous gas tungsten arc closure weld was developed for the US Department of Energy's primary container for the storage of plutonium bearing materials. The occurrence of porosity at the tie-in point of the closure weld was investigated. The primary cause of the porosity was linked to the geometry at the root of the closure weld joint. The present paper describes the mechanistic model that was developed to describe and predict the porosity. 相似文献
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《钢铁冶炼》2013,40(1):73-80
AbstractPlant trials with the addition of four different low carbon and medium carbon ferromanganese alloys to microalloyed engineering steels have been carried out at Ovako Steel, Hofors, Sweden. The process route for this type of steel at Ovako is electric arc furnace (EAF), ladle arc furnace (LAF), ASEA-SKF vacuum degasser, LAF and finally uphill teeming. For each ferromanganese alloy type, five experiments were accomplished by adding alloy at the ladle furnace station, i.e. 20 charges in total. During the experiments, liquid steel rapid solidification samples were taken to study the behaviour of inclusion formation and removal during ladle treatment. Also, samples for LSHR testing (liquid sampling hot rolling) were acquired for one heat of each of the ferromanganese containing alloys. Microinclusion assessments were carried out according to the method described in Swedish standard SS 111116. Macroinclusion assessments were carried out using immersed ultrasonic testing. Element analysis and mappings were done using a scanning electron microscope to establish the effect of ferromanganese addition on the composition of inclusions present in the steel. In samples taken 3 min after the ferromanganese addition to the LAF, about 30% of the analysed inclusions contain Al2O3, MnO and MnS. The Al2O3 content is concluded to originate from the deoxidation practice, while MnO and MnS contents are likely to originate from the addition of ferromanganese. The results also show that the addition of ferromanganese alloys leads to an increased amount of macroinclusions in the LAF up to 9 min after alloy addition. Steel samples taken after degassing but just before casting indicate that all the tested ferromanganese alloys give the same result with respect to the studied microinclusion characteristics at the end of ladle treatment. Last, the inclusion composition in the final steel samples is unrelated to the type of ferromanganese alloy used. In this case, the main compositions are Al2O3-MgO and MnS. 相似文献
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《Science & Technology of Welding & Joining》2013,18(5):436-442
AbstractType IV cracking refers to the premature failure of a welded joint due to an enhanced rate of creep void formation in the fine grained or intercritically annealed heat affected zone. A great deal of research effort has been directed at understanding the underlying mechanisms for this type of failure, but most have approached the problem from a metallurgical standpoint, and comparatively little effort has been directed at understanding the effects of welding variables. Here the effects of parameters such as the preheat temperature and heat input on the tendency for type IV failure in 9–12%Cr steels have been quantitatively estimated. These calculations have subsequently been verified experimentally to form the first systematic study of welding parameters on type IV cracking. The joint geometry and preheat temperature have been found to ameliorate type IV failures, while the effect of heat input is less significant. 相似文献
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跨平台数据传输一直是研究TCP/IP协议的一个重要方向,同时跨平台数据传输也是OSI通信的瓶颈。为了解决不同系统之间的通信,就需要研究TCP/IP协议关于跨平台数据传输方面的关键技术及原理,并在此基础上对当前各种解决方法的基本原理进行了比较分析。最后,详细分析了为实现跨平台传输目标的类型缓冲区技术,从而使我们对网络高层软件的开发和应用由一个清晰的了解。 相似文献
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《Science & Technology of Welding & Joining》2013,18(2):216-223
AbstractCreep rupture strength at 923 K and microstructural evolution of welded joints have been investigated for high boron–low nitrogen–9Cr heat resistant steels developed at the National Institute for Materials Science (Japan). Welded joints were prepared from plates containing 47–180 ppm boron using gas tungsten arc welding and Inconel type filler metal, and showed superior creep properties to those of welded joints of conventional high chromium steels such as P92 and P122. No type IV failure was observed in the boron steel welded joints. A large grained microstructure was observed in the heat affected zone heated to Ac 3 (Ac 3 HAZ) during welding, whereas the grains are refined at the same location in conventional steel welded joints. The simulated Ac 3 HAZ structures of the boron steels have a creep life almost equal to that of the base metal. Large grained HAZ microstructures and stabilisation of M23C6 precipitates are probable reasons for suppression of type IV failure and improved creep resistance of the boron steel welded joints. 相似文献