The present work describes the tensile flow and work hardening behavior of a high strength 7010 aluminum alloy by constitutive relations. The alloy has been hot rolled by three different ...cross-rolling schedules. Room temperature tensile properties have been evaluated as a function of tensile axis orientation in the as-hot rolled as well as peak aged conditions. It is found that both the Ludwigson and a generalized Voce–Bergström relation adequately describe the tensile flow behavior of the present alloy in all conditions compared to the Hollomon relation. The variation in the Ludwigson fitting parameter could be correlated well with the microstructural features and anisotropic contribution of strengthening precipitates in the as-rolled and peak aged conditions, respectively. The hardening rate and the saturation stress of the first Voce–Bergström parameter, on the other hand, depend mainly on the crystallographic texture of the specimens. It is further shown that for the peak aged specimens the uniform elongation (εu) derived from the Ludwigson relation matches well with the measured εu irrespective of processing and loading directions. However, the Ludwigson fit overestimates the εu in case of the as-rolled specimens. The Hollomon fit, on the other hand, predicts well the measured εu of the as-rolled specimens but severely underestimates the εu for the peak aged specimens. Contrarily, both the relations significantly overestimate the UTS of the as-rolled and the peak aged specimens. The Voce-Bergström parameters define the slope of Θ–σ plots in the stage-III regime when the specimens show a classical linear decrease in hardening rate in stage-III. Further analysis of work hardening behavior throws some light on the effect of texture on the dislocation storage and dynamic recovery.
Aluminum alloys, encompassed by AA 7055 alloy composition, having the nominal zinc content (i.e. 8
wt.%) but varying copper and magnesium contents across the alloy composition range were examined in ...the as-cast form by a combination of light microscopy, scanning electron microscopy (SEM), electron probe micro analysis (EPMA) and X-ray diffraction (XRD). It is observed that for all compositions, the second phases based on η(MgZn
2), T(Al
2Mg
3Zn
3) and S(Al
2CuMg) are present. The T phase dissolves copper up to 28
wt.%, whilst the S phase shows metastable solubility of zinc that may range up to 30
wt.%. In alloys with magnesium at the lower limit and the copper contents approaching the upper limit of the alloy composition, the θ phase (Al
2Cu) of the constituent binary Al–Cu system is further observed. The θ phase (Al
2Cu) does not dissolve either zinc or magnesium. Below the nominal composition, the alloys could be homogenized substantially using a commercially viable homogenization treatment leaving small amounts of undissolved S phase that does not contain any zinc.
Microwave processing has been emerging as an innovative sintering method for many traditional ceramics, advanced ceramics, specialty ceramics and ceramic composites as well as polymer and polymer ...composites. Development of functionally gradient materials: joining; melting; fibre drawing; reaction synthesis of ceramics; synthesis of ceramic powder, phosphor materials, whiskers, microtubes and nanotubes; sintering of zinc oxide varistors; glazing of coating surface and coating development have been performed using microwave heating. In addition, microwave energy is being explored for the sintering of metal powders also. Ceramic and metal nanopowders have been sintered in microwave. Furthermore, initiatives have been taken to process the amorphous materials (e.g. glass) by microwave heating. Besides this, attempt has been made to study the heating behaviour of materials in the electric and magnetic fields at microwave frequencies. The research is now focused on the use of microwave processing for industrial applications.
MONSOON MISSION Rao, Suryachandra A.; Goswami, B. N.; Sahai, A. K. ...
Bulletin of the American Meteorological Society,
12/2019, Letnik:
100, Številka:
12
Journal Article
Recenzirano
Odprti dostop
In spite of the summer monsoon’s importance in determining the life and economy of an agriculture-dependent country like India, committed efforts toward improving its prediction and simulation have ...been limited. Hence, a focused mission mode program Monsoon Mission (MM) was founded in 2012 to spur progress in this direction. This article explains the efforts made by the Earth System Science Organization (ESSO), Ministry of Earth Sciences (MoES), Government of India, in implementing MM to develop a dynamical prediction framework to improve monsoon prediction. Climate Forecast System, version 2 (CFSv2), and the Met Office Unified Model (UM) were chosen as the base models. The efforts in this program have resulted in 1) unparalleled skill of 0.63 for seasonal prediction of the Indian monsoon (for the period 1981–2010) in a high-resolution (~38 km) seasonal prediction system, relative to present-generation seasonal prediction models; 2) extended-range predictions by a CFS-based grand multimodel ensemble (MME) prediction system; and 3) a gain of 2-day lead time from very high-resolution (12.5 km) Global Forecast System (GFS)-based short-range predictions up to 10 days. These prediction skills are on par with other global leading weather and climate centers, and are better in some areas. Several developmental activities like coupled data assimilation, changes in convective parameterization, cloud microphysics schemes, and parameterization of land surface processes (including snow and sea ice) led to the improvements such as reducing the strong model biases in the Indian summer monsoon simulation and elsewhere in the tropics.
We propose a multivariate generalization of the univariate two-sample run test based on the shortest Hamiltonian path. The proposed test is distribution-free in finite samples. While most existing ...two-sample tests perform poorly or are even inapplicable to high-dimensional data, our test can be conveniently used in high-dimension, low-sample-size situations. We investigate its power when the sample size remains fixed and the dimension of the data grows to infinity. Simulated and real dataseis demonstrate our method's superiority over existing nonparametric twosample tests.
Friction stir welding (FSW) of thick aluminium sections will pave way for remarkable new defence applications, provided the accompanying challenges are successfully addressed. These challenges ...include elimination of tunnel defects, loss of strength in heat-treatable aluminium alloys, tool design and excessive process forces. Accounts of defect elimination, detailed micro-structural and mechanical characterization for thick section FSW are scarce in the published literature. Further, special strategies such as bobbin tool, pre-drilled hole for plunging and inverted double pass are generally deployed to overcome these challenges. This makes the process less productive and complex. In the present work, armor grade aluminum alloy AA2519-T87 plates having a thickness of 15.4 mm have been successfully joined with a joint efficiency of greater than 75% without supplementary strategies. The disparity in the effects of tool rotational speed and welding speed in the formation of a sound weld has been addressed in detail to enhance the understanding of FSW of thick sections. Micro-hardness measurements have been carried out throughout the transverse cross-section of the welds and correlated with different zones and their corresponding microstructures. Scanning electron microscopy and X-ray energy dispersive spectroscopy have been used to characterize the coarse phase particles present in the weld zones.
Graphic Abstract
Al–Cu–Li–Mg–Ag–Zr alloy AA2195, in the form of 4mm thick sheets, was heat treated to T87 temper with the pre-aging cold work provided by a combination of 5% cold rolling followed by 2% stretching. ...The tensile properties of the material were evaluated at ambient and cryogenic temperatures (i.e. −196°C and −253°C). Transmission electron microscopy of the heat treated (i.e. T87 treated) material revealed that the major strengthening precipitate is indeed the T1 (Al2CuLi) phase nucleated on the {111}Al planes. In addition, θ′ metastable Al2Cu (θ) precipitates on {100}Al planes, and “plate like features” lying on {111}Al planes were further observed. The one atom layer thick “plate like features” have the same crystal structure as that of the matrix Al. The possibility of such “plate like features” being either the early stages of the Ω phase (i.e. a chemically modified coherent form of θ-Al2Cu phase) in the constituent Al–Cu–Mg–Ag system or the evolutionary stages of the T1 phase itself is discussed.
We report the effect of BaO addition on thermal, crystallization, electrical and mechanical behavior of the magnesium lanthanum alumino borosilicate glass-ceramics. The glass forming region has been ...found to be quite narrow with respect to BaO content. Casting and annealing of completely transparent and amorphous glasses within this system has been possible only at an optimum BaO content of 25
mol% without any La
2O
3 and Al
2O
3. On further optimization of the developed glasses in terms of different borosilicate ratios, one of the developed compositions having MgO and BaO content of 22 and 25
mol% respectively, with a glass former ratio of 3 (SiO
2:B
2O
3) has been found to be quite promising in terms of its mechanical property, excellent joining, minimum chemical interaction and lowest leak-rate with the metallic interconnect such as Crofer22APU, and thus fulfills the major requirements for SOFC sealing application.
Vibrio cholerae O1 El Tor variant strains produced much more cholera toxin than did prototype El Tor strains. The amount of cholera toxin produced by El Tor variant strains both in vitro and in vivo ...was more or less equivalent to that produced by classical strains.
PDF
