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961.
Vijaya L. Manugula G. Madhusudhan Reddy E. Rajendra Kumar K. Bhanu Sankara Rao 《Science & Technology of Welding & Joining》2018,23(8):666-676
Full penetration friction stir welding was conducted on 12?mm thick reduced activation ferritic–martensitic steel at tool rotational speeds of 500 and 900?rev?min?1. Comparator welds at 500?rev?min?1 were also produced in 6?mm thick reduced activation ferritic–martensitic steel plate to evaluate section thickness effects. Increase in section thickness led to an increase in heat input, which strongly influenced the microstructure evolution in stir zone (SZ), thermo-mechanical affected zone and the overall hardness in the SZ of this steel. In the as-welded condition, the base metal microstructure was significantly altered and resulted in carbide-free grain boundaries. The desirable microstructure and mechanical properties were achieved by subjecting the as-welded joints to appropriate post-weld heat treatments. 相似文献
962.
G. Srinivasa Rao K. Srinivasa Rao P. Srinivasa Rao S. R. Koteswara Rao G. Madhusudan Reddy 《Protection of Metals and Physical Chemistry of Surfaces》2018,54(5):866-875
Present work mainly focused on the pitting and stress corrosion cracking behavior of AFNOR7020 aluminium alloy friction stir welds and compared those results with the base material. Initially, microstructural studies, TEM, microhardness tests, tensile tests and general corrosion properties of the welds were investigated. The elongated grains present in the base material have been transformed into superfine grains in the weld nugget. Transmission electron micrographs obtained from various regions of the weld indicated that almost all strengthening precipitates dissolved in the nugget region while partial dissolution of precipitates occurred in the thermo-mechanically affected zone and coarsening occurred in heat affected zone. Hardness in the weld nugget was found to be very nearer to the base material without considerable difference. The welds showed superior joint efficiency of 85% in terms of the yield strength and 95% in terms of ultimate tensile strength. General corrosion resistance of the welds was better than that of the base material at different pH value and spraying time. Pitting corrosion studies revealed that less significant difference in pitting corrosion resistance has been observed between the weld nugget and the base material. It was found that the susceptibility towards stress corrosion cracking is relatively more in base metal compared to welded joints. It has been concluded that friction stir welding plays a very important role in corrosion properties of the AFNOR7020 aluminium alloy. 相似文献
963.
Kenji Watanabe Susumu Nakajima Torajiro Fujiwara Kyoichiro Yoshii G. Venkatappa Rao 《Soils and Foundations》2021,61(1):218-238
The railway embankment applied to high-speed railways is required to have high performance in terms of strength and deformation characteristics. Especially in the case of railway embankments that support slab tracks, the allowable settlement is very small. There are two technical challenges in constructing high-speed rail embankments to support slab tracks in India. The first challenge is dealing with problematic black cotton soil (BCS), which is widely distributed in India but very unusual soil in Japan. The second challenge is posed by the strict deformation requirement in the construction of the embankments. In this study, a 6 m-high test embankment was constructed on BCS in India. The deformation of the embankment and changes in water content were measured over a period of 18 months. In the construction of the test embankment, two different BCS countermeasures were applied. The results of the tests on this embankment were compared with those from an embankment without countermeasures. Complicated deformation behaviors, including settlement and the uplift of embankment, were observed in the section without countermeasure. However, in the embankment with cement-mixed gravelly soil (CGS) slab improvement with geosynthetics, the much lower amplitude of embankment deformation is evidence of the effectiveness of this countermeasure. The cohesive non-swelling soil (CNS) layer applied immediately below the embankment to reduce the water content fluctuation of BCS was not effective enough for use for high-speed railway embankment. Besides determining the technical challenges for the BCS countermeasures, the results of this study confirmed that a high-performance embankment can be constructed with Indian embankment material by performing sufficient compaction management. 相似文献
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Routing for disruption tolerant networks: taxonomy and design 总被引:5,自引:0,他引:5
Thrasyvoulos Spyropoulos Rao Naveed Bin Rais Thierry Turletti Katia Obraczka Athanasios Vasilakos 《Wireless Networks》2010,16(8):2349-2370
Communication networks, whether they are wired or wireless, have traditionally been assumed to be connected at least most
of the time. However, emerging applications such as emergency response, special operations, smart environments, VANETs, etc.
coupled with node heterogeneity and volatile links (e.g. due to wireless propagation phenomena and node mobility) will likely
change the typical conditions under which networks operate. In fact, in such scenarios, networks may be mostly disconnected,
i.e., most of the time, end-to-end paths connecting every node pair do not exist. To cope with frequent, long-lived disconnections,
opportunistic routing techniques have been proposed in which, at every hop, a node decides whether it should forward or store-and-carry a message.
Despite a growing number of such proposals, there still exists little consensus on the most suitable routing algorithm(s)
in this context. One of the reasons is the large diversity of emerging wireless applications and networks exhibiting such
“episodic” connectivity. These networks often have very different characteristics and requirements, making it very difficult,
if not impossible, to design a routing solution that fits all. In this paper, we first break up existing routing strategies
into a small number of common and tunable routing modules (e.g. message replication, coding, etc.), and then show how and when a given routing module should be used, depending on the set of network characteristics exhibited by the wireless application. We further attempt to create a taxonomy for intermittently connected networks. We
try to identify generic network characteristics that are relevant to the routing process (e.g., network density, node heterogeneity, mobility patterns) and dissect different
“challenged” wireless networks or applications based on these characteristics. Our goal is to identify a set of useful design guidelines that will enable one to choose an appropriate routing protocol for the application or network in hand. Finally, to demonstrate
the utility of our approach, we take up some case studies of challenged wireless networks, and validate some of our routing
design principles using simulations. 相似文献
970.
Huang C.-Y. Huang T.-S. Cheng C.-Y. Chen Y.-C. Wan C.-T. Rao M. V. M. Su Y.-K. 《Photonics Technology Letters, IEEE》2010,22(5):305-307