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排序方式: 共有665条查询结果,搜索用时 15 毫秒
41.
German Castillo Hervé Wargnier Michel Danis Yves Brechet 《Advanced Engineering Materials》2009,11(11):938-944
After translation, the first stages traditionally involved in the materials selection are filtration and classification, which require formulation of criteria (constraints or objectives) deduced from information written in the set of material requirements. These criteria, which are representative of the behavior of the material and the studied structure, must be formulated analytically in order to be used during selection stage. However, for complex behavior, analytical processing of models is no longer possible and it can be replaced by a combination of numerical resolution methods and an optimization method which make it possible to obtain approximate formal expressions of the criteria. In this paper, a complete selection method is proposed. The method is applied to the constraints as well as the objectives, in order to carry out the filtration and classification stages at the same time. The study of the thermomechanical behavior of a machine tool frame has been used to demonstrate the validity of the proposed method. 相似文献
42.
A mathematical model which makes it possible to calculate the heat-protection properties of the composite coating ceramic microspheres–binder is proposed. The model takes account of the optical and thermophysical properties of the components and the optical properties of a substrate. It is shown that the decrease in the heat loss due to suppression of its radiative component by the coating in question can reach more than 50%. Under certain conditions, the heat-insulation effect can be absent or even inverted, i.e., the presence of the coating is capable of resulting in an increase in the heat flux from the surface being protected. Comparison of the data of the performed full-scale experiment and the calculations based on the proposed model showed that the latter adequately reflects the actual process of heat transfer and can be used for calculating the heat-protection properties of coatings representing a compound of a binder and ceramic microspheres. 相似文献
43.
Deborah C. Blaine Seong Jin Park Randall M. German Pavan Suri 《Metallurgical and Materials Transactions A》2006,37(9):2827-2835
One of the current challenges facing the particulate materials industry is developing simple, accurate models to predict sintered
properties. Work-of-sintering concepts, where time-temperature integrals are used in such models, offer a solution to this
problem. In this study, the master sintering curve concept is applied to several powder metal systems: 17 to 4PH stainless
steel, 316L stainless steel, nickel, niobium, tungsten heavy alloys with two different compositions, and molybdenum. A detailed
explanation of the construction of these curves is given, including methods used to calculate the apparent activation energy
for sintering and to curve-fit experimental data to a sigmoid function describing the master sintering curve. Discussion of
the results shows that the master sintering curve can be applied to powder metal systems, even those that use liquid phase
during sintering. 相似文献
44.
Densification behavior of tungsten heavy alloy based on master sintering curve concept 总被引:1,自引:0,他引:1
S. J. Park Randall M. German J. M. Martin J. F. Guo J. L. Johnson 《Metallurgical and Materials Transactions A》2006,37(9):2837-2848
The master sintering curve (MSC) theory is modified by substituting the densification ratio (φ) for the densification parameter
(ψ) to identify regions where shrinkage occurs by a similar combination of sintering mechanisms. The modified MSC theory is
used to analyze the results of dilatometry experiments conducted with W-Ni-Fe heavy alloys, in which a phase change occurs
during sintering. Apparent activation energies for sintering in three regions (solid state, transition, and liquid phase)
are calculated. These activation energies are compared with experimental values for diffusion and other mass-transport phenomena
to identify the dominant mechanisms in each region. A series of master sinter curves for varying W contents are developed
into a master sintering surface that includes tungsten content and integral work. 相似文献
45.
M. L. German V. A. Borodulya E. F. Nogotov 《Journal of Engineering Physics and Thermophysics》2000,73(6):1156-1165
An engineering procedure for calculating the thermal regime of the furnace chambers of firetube boilers with a deadend furnace is given. The procedure proposed is devoid of many drawbacks that are inherent in the standard method for calculating boiler units and permits more accurate allowance for the special features of combined energy exchange in furnace chambers of boilers that differ significantly in type and size from traditional ones. 相似文献
46.
The luminescence of AgBr and AgBrCl crystals doped with Pr(3+) rare-earth ions was investigated in the visible and infrared spectral ranges. We measured the excitation, emission, and absorption spectra as well as the kinetic parameters over a broad temperature range. The strong influence of the silver halide composition on Pr(3+) ions spectroscopic properties was revealed. We calculated useful optical parameters for Pr:AgBr crystals by using the Judd-Ofelt approximation. Good agreement between the theoretical and the measured parameters was obtained. 相似文献
47.
Ramnath Ganesan Anthony Griffo Randall M. German 《Metallurgical and Materials Transactions A》1998,29(2):659-664
Liquid phase sintering (LPS) is a common technique to consolidate materials that are difficult to process by fusion techniques,
such as tungsten heavy alloys. One of the major processing difficulties associated with liquid phase sintered alloys is component
distortion and loss of component shape. In LPS, this distortion is the result of viscous flow driven by curvature effects
and gravity. A finite element model is developed for viscous flow of the semisolid sintering structure using Stokes equations.
This model considers solid volume fraction and effective viscosity of the solid-liquid mixture. The simulation predictions
are compared to distortion results for microgravity and ground-based sintering experiments, and they show good agreement.
The model results indicate that the effective semisolid viscosity is significantly greater than the liquid metal viscosity.
Hence, future work needs to quantitatively examine the factors controlling viscosity and the benefits from such high viscosities
in liquid phase sintered systems. 相似文献
48.
N Linder M Tsur J Kuint B German E Birenbaum R Mazkereth D Lubin B Reichman A Barzilai 《Canadian Metallurgical Quarterly》1998,157(6):502-504
The New Doctor paper recently published by the General Medical Council outlines the primarily educational role of preregistration house officers. This article illustrates one innovative way in which this is being implemented simultaneously with a significant service provision, often increasing the standard of patient care. 相似文献
49.
50.
Alfassi ZB Zlatin T Manor O Dubinsky S German U 《Radiation protection dosimetry》2004,110(1-4):207-211
Most high-efficiency interactions for neutron detection are with thermal neutrons, and the detection of the prompt gamma radiation emitted as a result of thermal neutron absorption in specific materials was sometimes used. These materials are named converters, the most widespread being 10B, 113Cd or 73Ge (the last two materials are detector materials themselves for CdZnTe and HPGe detectors). However, for these materials, the main gamma-ray energies are relatively low (in the region 473-600 keV), and there are interferences from other gamma rays present in background. Different combinations of moderator-converter-detector systems were employed to optimise the system efficiency and signal-to-background ratio, using B, Cd, Gd and Cl converters and HPGe, NaI(Tl) and BGO detectors. When using a Cl converter, the 1164.7 keV peak seems to be a good choice when a HPGe spectrometer is used. A very practical material containing chlorine is PVC. 相似文献