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排序方式: 共有383条查询结果,搜索用时 15 毫秒
1.
Effect of boron on the low-cycle fatigue behavior and deformation structure of INCONEL 718 at 650 °C
L. Xiao M. C. Chaturvedi D. L. Chen 《Metallurgical and Materials Transactions A》2004,35(11):3477-3487
Symmetrical push-pull low-cycle fatigue (LCF) tests were performed on INCONEL 718 (IN718) containing 12, 29, 60, and 100 ppm
B at 650 °C. The results showed that all the alloys experienced a relatively short period of initial cyclic hardening at low
strain amplitudes, followed by a regime of saturation or slightly continuous cyclic softening. The initial cyclic hardening
phase decreased with increasing strain amplitudes, and disappeared at the high strain amplitudes. A serrated flow was observed
in the plastic regions of cyclic stress-strain hysteresis loops. The saturated cyclic stress amplitude at a given strain amplitude
was highest for the alloy with 60 ppm B, and lowest for the alloy with 12 ppm B. The LCF lifetime increased with increasing
B concentration up to 60 ppm, and then decreased as the B content increased from 60 to 100 ppm. Fractographic analysis suggested
that the fracture mode changed from intergranular to transgranular cracking as the B concentration increased. The characteristic
deformation microstructures produced by LCF tests at 650 °C, examined via transmission electron microscopy, were regularly spaced arrays of planar deformation bands on {111} slip planes in all four
alloys. A ladderlike structure was observed in some local regions in the alloy with 12 ppm B. Heavily deformed planar deformation
bands were observed in the fatigued specimens with 100 ppm B. The mechanism of improvement in the LCF life of IN718 due to
B addition is discussed. 相似文献
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Spina bifida, a congenital deformity of the posterior wall of vertebrae of the spine, is a midline defect of skin, vertebral arches and neural tube, usually in the lumbosacral region. Its incidence is reported to be 0.2 to 0.4 per 1000 live births. Various hypotheses have been put forward as etiological factors for spina bifida including consumption of potato affected by blight and hardness of drinking water but these have not been proven. Two groups of 50 randomly chosen children were established. The study group consisted of children aged 5 to 12 years, weighing 15 to 30 kg, consuming fluoride rich drinking water (4.5 and 8.5 ppm fluoride; WHO permissible limit is 1.5 ppm fluoride), and manifesting either clinical, dental and/or skeletal fluorosis. The control group consisted of age and weight-matched children, consuming less than or equal to 1.5 ppm fluoride in drinking water and not showing any evidence of fluoride toxicity. These children were evaluated for antenatal history, general clinical examination (especially for dimples, tufts of hair, haemangioma on skin throughout the length of spine), other congenital abnormalities, evidence of fluoride toxicity, biochemical estimation for fluoride levels in blood and serum and by skiagrams of the spine to examine for the presence of spina bifida occulta. A total of 22 (44%) of the 50 children in group A, the study group, and 6 (12%) of the 50 children in group B, the control group, revealed spina bifida occulta in the lumbosacral region.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
5.
S. Chaturvedi C. Dunne Z. Ashktorab R. Zachariah B. Shneiderman 《Computer Graphics Forum》2014,33(8):52-68
An important part of network analysis is understanding community structures like topological clusters and attribute‐based groups. Standard approaches for showing communities using colour, shape, rectangular bounding boxes, convex hulls or force‐directed layout algorithms remain valuable, however our Group‐in‐a‐Box meta‐layouts add a fresh strategy for presenting community membership, internal structure and inter‐cluster relationships. This paper extends the basic Group‐in‐a‐Box meta‐layout, which uses a Treemap substrate of rectangular regions whose size is proportional to community size. When there are numerous inter‐community relationships, the proposed extensions help users view them more clearly: (1) the Croissant–Doughnut meta‐layout applies empirically determined rules for box arrangement to improve space utilization while still showing inter‐community relationships, and (2) the Force‐Directed layout arranges community boxes based on their aggregate ties at the cost of additional space. Our free and open source reference implementation in NodeXL includes heuristics to choose what we have found to be the preferable Group‐in‐a‐Box meta‐layout to show networks with varying numbers or sizes of communities. Case study examples, a pilot comparative user preference study (nine participants), and a readability measure‐based evaluation of 309 Twitter networks demonstrate the utility of the proposed meta‐layouts. 相似文献
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The polarographic behaviour of diisopropylaminoethanethiol HCl (RSH) has been studied in presence of 0·1 M LiCl at the dme. The effects of pH, supporting electrolyte, concentration, drop time and temperature on the characteristics of the wave have been investigated. The curves consist of two waves—a small pre-wave followed by a normal anodic wave over the entire pH range (2·60–12·60). The maximum number of moles absorbed on unit area is 3·98 × 10?10 mole/cm2, ie 2·4 × 1014 molecules/cm2, which corresponds to an area 41·6 Å2 per adsorbed molecule. The adsorption coefficient and molar adsorption energy are 6·34 × 102 and 26·34 kcal/mole respectively. The electrode reaction is reversible, diffusion-controlled and involves a one-electron tranfer process. The pK of the ?SH group is 10·6. Controlled-potential electrolysis, interaction with mercuric chloride and mathematical analysis reveal the depolarization of mercury with the formation of a Hg(I) complex, mercurous mercaptide RSHg, which rapidly changes to more stable mercuric complex (RS)2Hg. 相似文献
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Stabilizing controllers are developed for a 3D pendulum assuming that the pendulum has a single axis of symmetry and that the center of mass lies on the axis of symmetry. This assumption allows development of a reduced model that forms the basis for controller design and global closed-loop analysis; this reduced model is parameterized by the constant angular velocity component of the 3D pendulum about its axis of symmetry. Several different controllers are proposed. Controllers based on angular velocity feedback only, asymptotically stabilize the hanging equilibrium. Then controllers are introduced, based on angular velocity and reduced attitude feedback, that asymptotically stabilize either the hanging equilibrium or the inverted equilibrium. These problems can be viewed as stabilization of a Lagrange top. Finally, if the angular velocity about the axis of symmetry is assumed to be zero, controllers are introduced, based on angular velocity and reduced attitude feedback, that asymptotically stabilize either the hanging equilibrium or the inverted equilibrium. This problem can be viewed as stabilization of a spherical pendulum. 相似文献
8.
D.A. AkinladeW.F. Caley N.L. RichardsM.C. Chaturvedi 《Materials Science and Engineering: A》2011,528(3):996-1002
The effect of the addition of 1 and 3 w/o Ti to a quaternary (Ni-Cr-Fe-Al) alloy on the phase transformations that might occur in the material on sintering were simulated using a thermodynamic modelling tool. These predictions were subsequently compared with experimental results obtained by X-ray diffraction and metallography. As well, the onset of melting and the transformation temperature of the Ti modified alloys were corroborated by Differential Scanning Calorimetry (DSC). From SEM and point count analyses, the microstructure, including the % porosity and volume fraction of gamma prime precipitates, remained relatively unchanged from the quaternary without Ti. This may have been due to the presence of sub-micron precipitates not detected in the Ti-containing samples. However, an increase in lattice parameters on adding both 1 and 3 w/o Ti to the quaternary was determined from X-ray diffraction measurements. Finally, the software modelling provided a reasonable prediction for both microstructure and thermal processing thereby offering a means to simulate both design and characterisation of the experimental material, both during sintering and on cooling. 相似文献
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