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21.
A series of experiments were carried out on three commercial steels to explore the possibility for characterizing tempered martensite embrittlement (TME) by Rockwell, macro-, and micro-Vickers hardness tests. The results indicate distinct hardness peaks in two steels and an inflection in the other around the TME temperature. A new analytical approach for examining the slope of hardness-tempering temperature plots appears to reveal the TME phenomenon more sensitively. Dilatometric examinations substantiate that the temperature of hardness peak/inflection occurs beyond the second stage of tempering. 相似文献
22.
The concept of control signals is fundamental to digital design. It evokes the notion of one or more signals that influence computation on other signals in a system, and regulate the behavior of the system. A formal definition of control signals is presented. It is argued that knowledge of the control signals in a complex design such as a microprocessor or a computer is crucial to the comprehension and specification of the design and that knowledge of the control signals of a design leads to a more efficient hardware implementation. The identification of control signals in two microprocessors are presented as examples 相似文献
23.
Rates of coke formation during steam pyrolysis of naphtha have been investigated in a jet-stirred reactor both for sodium silicate coated and uncoated Inconel 600 surfaces in the temperature range of 1078–1108 K. Coke formation rates were significantly reduced on sodium silicate coated plates due to the passivation of the metal surface. However, the coking rates gradually increased with successive decokings of the coated surface. 相似文献
24.
The superplastic properties of a rapidly solidified, high strength P/M Al alloy and the same alloy reinforced with SiC particulates
(SiC
p
) have been studied. To prepare superplastic test materials, a matrix alloy powder of composition 7.2Zn-2.4Mg-2Cu-0.2Zr-0.12Cr-0.2Co
(Kaiser PM-64) and the powder mixed with 10 to 20 vol pct SiC
p
(~5 μm diameter) were thermomechanically processed to very fine equiaxed grain structures of ~6 μm and ~8 μm, respectively.
Superplasticity in these materials was evaluated by characterizing (1) high temperature stability, (2) dynamic grain growth,
(3) strain rate sensitivity, (4) flow stress behavior, (5) cavitation and cavitation control, and (6) total superplastic strain.
It was observed that the PM-64 alloy could achieve a total elongation of over 800 pct, while the SiCp reinforced alloy could attain an elongation greater than 500 pct before failure. Also, it was shown that with the use of
hydrostatic pressure during superplastic flow, cavitation could be controlled. Observations were made of the effect SiC
p
reinforcement particles had on the superplastic flow stress behavior. Interpretations are proposed to explain the role of
particulates during superplastic straining. 相似文献
25.
G. G. Krishna Murthy A. Ghosh S. P. Mehrotra 《Metallurgical and Materials Transactions B》1989,20(1):53-59
A macroscopic, steady state energy balance model has been formulated to describe mixing phenom-ena in a liquid bath stirred
by injecting gas through a straight nozzle fitted axially at the bottom of the vessel. This, along with experimental data
on a water model previously reported, was employed to make predictions. Input energy terms considered in the model consist
of buoyancy energy and empirically determined fraction of gas kinetic energy. Dissipation of energy was attributed to liquid
circulation and bubble slip. The two-phase plume was assumed to be a truncated cone whose dimen-sions depended upon operating
conditions. Numerical solution of model equations gave liquid velocity and gas hold-up inside the plume as well as liquid
circulation rate and liquid velocity in the region outside the plume. Influence of process variables, e.g., gas flow rate,
bath height, and nozzle diameter, have been predicted. Validity of the model has been established by comparing some pre-dicted
entrainment ratios with those experimentally measured by other investigators. Empirical cor-relations to predict circulation
time and circulation number have been proposed. Circulation number was found to vary between 2 and 12 in contrast to the existing
assumption in the literature of a con-stant value of 3. Usefulness of these correlations in predicting mixing time for industrial
vessels has been demonstrated.
Formerly a Graduate Student in the De-partment of Metallurgical Engineering at the Indian Institute of Technol-ogy, Kanpur 相似文献
26.
27.
DJ Benos BH Hahn JK Bubien SK Ghosh NA Mashburn MA Chaikin GM Shaw EN Benveniste 《Canadian Metallurgical Quarterly》1994,91(2):494-498
Infection by human immunodeficiency virus type 1 (HIV-1) is often complicated by a variety of neurological abnormalities. The most common clinical syndrome, termed acquired immunodeficiency syndrome (AIDS) dementia complex, presents as a subcortical dementia with cognitive, motor, and behavioral disturbances and is unique to HIV-1 infection. The pathogenesis of this syndrome is poorly understood but is believed to involve interactions among virally infected macrophages/microglia, astrocytes, and neurons. In this study, we show that exposure of primary rat and human astrocytes to heat-activated HIV-1 virions, or to eukaryotically expressed HIV-1 and HIV-2 envelope glycoproteins (gp120) stimulates amiloride-sensitive Na+/H+ antiport, potassium conductance, and glutamate efflux. These effects are blocked specifically by amiloride, an inhibitor of Na+/H+ antiport and by the selective removal of gp120 with immobilized monoclonal antibody. As a result of modulation of astrocytic function by gp120, the ensuing neuronal depolarization and glutamate exposure could activate both voltage-gated and N-methyl-D-aspartate-regulated Ca2+ channels, leading to increases in intraneuronal Ca2+ and neuronal death. These findings implicate the astrocyte directly in the pathogenesis of AIDS dementia complex. 相似文献
28.
H. S. Tripathi B. Mukherjee S. K. Das A. Ghosh G. Banerjee 《Bulletin of Materials Science》2003,26(2):217-220
Mullite was developed by reaction sintering of sillimanite beach sand and calcined alumina. Two varieties of sillimanite beach
sand viz. S and Z having different compositions were selected. Synthesis and properties of mullite were very much dependent
on the sillimanite beach sand composition. Presence of higher amount of impurities in the Z-variety of sillimanite sand favours
the densification by liquid phase formation. Presence of zircon in Z-variety increases the hardness and fracture toughness.
Alumina addition improves the mechanical/thermomechanical properties of the samples. Mullite retains the usual orthorhombic
habit of sillimanite. Rounded to sub rounded zirconia dispersed within the mullite matrix of the sample ZA is noticed. 相似文献
29.
Dhyanjyoti Deka Deepu S. Joseph Somnath Ghosh Michael J. Mills 《Metallurgical and Materials Transactions A》2006,37(5):1371-1388
This paper develops an experimentally validated computational model based on crystal plasticity for the analysis of two-phase
α/β Ti-6242 polycrystalline alloys. A rate-dependent elastic-crystal plasticity model is incorporated in this model to accommodate
anisotropy in material behavior and tension-compression asymmetry inherent to this alloy. A combination of microtesting, orientation
imaging microscopy, computational simulations, and minimization process, involving genetic algorithms, is implemented in this
study for careful characterization and calibration of the material parameters. Size effects are considered in this analysis
through a simple scaling process. A homogenized equivalent model of the primary α with transformed β colonies is developed
for incorporation in the Ti-6242 FE model. The polycrystalline Ti-6242 computational model incorporates accurate phase volume
fractions, as well as statistically equivalent orientation distributions to those observed in the orientation imaging microscopy
scans. The effects of orientation, misorientations, and microtexture distributions are investigated through simulations by
this computational model. The model is used to simulate constant strain rate and creep tests in compression and tension, and
the results are compared with experiments. The effects of microstructure and creep-induced load-shedding on the localization
of microstructural stresses and strains are studied for potential crack initiation criteria. 相似文献
30.
The tensile properties of jute make it a suitable raw material for asphalt overlay (A/O) fabric. In this study, the thermal stability of jute under conditions of asphalt overlaying process was investigated and the compatibility of jute with asphalt was assessed through experimentation on jute–asphalt composites under mechanical and hygral loads. Fourier transform infra red (FTIR) spectroscopic study revealed probable chemical bonding between jute and asphalt. The test for ascertaining the capability of asphalt encasement for protecting jute against biodegradation under enzymatic attack was found positive. A 6‐month hygral treatment, of the jute–asphalt composite, showed significant increase in modulus of the material. The results indicate that although the strength of jute deteriorates by about 10% under asphalt overlaying condition, the overall tensile behavior of jute fabric–asphalt composite material is considerably superior to that of the pure jute fabric, even under biological and extended hygral loading conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献