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801.
Jong Un Lee Sang-Hoon Kim Wan-Kuen Jo Won-Hwa Hong Woong Kim Jun Ho Bae Sung Hyuk Park 《Metals and Materials International》2018,24(4):730-737
Grain-refined AZ92 (GR-AZ92) alloy with superior tensile properties is developed by adding 1 wt% Zn and a very small amount of SiC (0.17 wt%) to commercial AZ91 alloy for enhancing the solid-solution strengthening effect and refining the crystal grains, respectively. The homogenized GR-AZ92 alloy with an average grain size of 91 μm exhibits a tensile yield strength (TYS) of 125 MPa, ultimate tensile strength (UTS) of 281 MPa, and elongation of 12.1%, which are significantly higher than those of AZ91 alloy with a grain size of 420 μm (TYS of 94 MPa, UTS of 192 MPa, and elongation of 7.0%). The peak-aging time of GR-AZ92 alloy (8 h) is significantly shorter than that of AZ91 alloy (32 h) owing to a larger amount of grain boundaries in the former, which serve as nucleation sites of Mg17Al12 precipitates. A short-aging treatment for less than 1 h of the GR-AZ92 alloy causes an effective improvement in its strength without a significant reduction in its ductility. The 30-min-aged GR-AZ92 alloy has an excellent combination of strength and ductility, with a TYS of 142 MPa, UTS of 304 MPa, and elongation of 8.0%. 相似文献
802.
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
803.
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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807.
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
808.
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
809.
By heating H3BO3 with urea in 1 : 6 molar ratio, nanoparticles and nanotubes of BN are obtained. The urea–boric acid reaction can also be exploited to obtain graphene analogues of BN, with the number of layers depending on the relative proportions of the two reactants. Synthesis with a high proportion of urea yields a product containing graphene analogues of BN with an average of 2 layers. The surface area of BN increases with the decreasing number of layers, and the high-surface-area BN also exhibits high CO2 adsorption. Few-layer BN can be solubilized by interaction with Lewis bases. Nanopans and nanosheets formed by graphene-like BN are generated by the vapor phase reaction of NH3 and BBr3 at 1223 K. Nanopans of BN, being reported for the first time, have a bottom comprising single-layer BN and a wall of 0.7 nm height. The average inner volume of the nanopan is around 400 nm3. 相似文献
810.
Anwesha Maity Dipul Kalita Tarun Kumar Kayal Tridip Goswami Omprakash Chakrabarti Himadri Sekhar Maiti Paruchuri Gangadhar Rao 《Ceramics International》2010,36(1):323-331
Synthesis of SiC ceramic from processed cellulosic bio-precursor was investigated. Bamboo (Bambusa tulda Roxb.) plants abundantly available in the Jorhat district of Assam, India, were selected for extraction of fibers following Kraft pulping method and bleached bamboo pulp fibers were suitably cast in the form of rectangular boards. Coir fibers available in the Alleppy district of Kerala, India, were initially digested with dilute alkali, mixed with cellulose acetate solution, air dried and then hot-pressed at 140 ± 5 °C under 2.0–2.5 MPa pressure to make rectangular boards. Well-characterized processed bio-precursors were pyrolysed at ~800 °C under flowing N2 atmosphere to prepare the bio-carbonaceous preforms (carbon templates) which showed nearly uniform shrinkages in all directions. Coir fiber composite board carbon showed lower pyrolytic weight loss (~66%), higher density (0.49 g cm?3), lower porosity (~58%) and narrower pore diameter (10 μm) compared to the cast bamboo pulp fiber board carbon. The carbon samples showed perfect retention of fibrous morphological features of hierarchically grown bio-structures. Ceramization of carbon templates could be done by reactive melt silicon infiltration into porous channels at ~1600 °C under vacuum. The final ceramics were adequately dense (%theoretical density > 99%), showed negligible linear dimensional changes (indicating net-dimension formation capability), presence of crystalline Si and SiC phases and duplex microstructure with complete preservation of fibrous architecture of plant bio-structure. The Si/SiC ceramic composite synthesized from coir fiber board gave room temperature 3-point flexural strength and Young's modulus values of 121 MPa and 276 GPa, respectively. Both the ceramic composites showed adequate oxidation resistance during heating at 1300 °C for 7 h in air. 相似文献