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991.
This article describes the results of an investigation concerning with the failure of a pipe which was carrying oil from the
control oil unit to the steam turbine control valves servomotor. The failure was in the form of a crack, propagating horizontally
along the pipe. The crack initiated on the outside of the pipe. The cause of the failure was investigated by conducting visual
examination, detailed macro and microstructural examinations and determining the composition of material from the failed pipe.
The composition of the pipe material was analyzed by atomic absorption spectrometer. The failure of the oil pipe was attributed
to stress corrosion cracking. The pipe material is A312 TP 304L. Recommendation to minimize such failures includes coating
the pipe to prevent contact with chloride from the surrounding marine environment. 相似文献
992.
Results are presented for binary intermolecular interactions and thermophysical properties in the temperature range between
70K and 1,000K of gaseous fluorine (F2), and between 200K and 1,000K of chlorine (Cl2), bromine (Br2), and iodine (I2). Our studies are carried out with an (n − 6) Lennard-Jones temperature-dependent potential (LJTDP). The underlying model takes into account the influence of vibrational
excitations on the equilibrium distance R
m(T) and potential well depth e(T){\varepsilon(T)} . The potential parameters at T = 0K have been obtained by minimization of the sum of squared deviations between experimentally determined and calculated
second pVT- and acoustic virial coefficients, B and β, and viscosities η, normalized to their relative experimental error a
exp. The majority of the available experimental data are well reproduced within their experimental errors. Tables and fitting
formulae for a fast and reliable prediction of the thermophysical properties and potential parameters are also presented. 相似文献
993.
U. Götze Th. Weber C. Linke A. Schmidt 《Materialwissenschaft und Werkstofftechnik》2009,40(7):566-572
Target Costing for Materials – Potentialities and Methodology Target Costing is a standard instrument of cost management in business administration, but hardly mentioned in the economic oriented literature on material sciences. Nevertheless there are high potentialities for developers, producers, or users of materials regarding the improvement of efficiency. Therefore, this article will present these potentialities of a material oriented Target Costing. Besides, the general methodology of Target Costing will be modified to meet the specifics of materials from the perspectives of users of materials on the one hand and developers respectively producers of materials on the other. 相似文献
994.
The relative activity of the potential slip systems in Sn is examined by comparing an experiment of a single shear lap deformation
with simulations using the viscoplastic self-consistent crystal plasticity model developed by Lebensohn and Tomé. In a single
shear lap specimen made using eutectic Sn-Ag solder on copper pull tabs, the initially polished side was characterized using
orientation mapping before and after 0.8 shear deformation at 25°C at a shear strain rate of 0.1/s. The critical resolved
shear stress of potential slip systems and the rate sensitivity was altered by trial and error until good agreement between
experimentally observed and computed texture was obtained. This result indicated that slip on {101) and {211) planes is much
more difficult to activate than on other slip systems for the grain orientations present in this sample. This particular sample
showed much activity on the {010)〈101] slip system, but the activation of this slip system may be related to the initial dominant
orientation in the specimen. This result is compared with literature and related experiments on ball grid arrays in a companion
paper in this volume that show similar trends. As lead-free solder joints are commonly single crystals or multicrystals, this
particular result is not indicative of lead-free solder joints as a whole, but must be interpreted in the context of a larger
data set. 相似文献
995.
The paper proposes a novel approach to model the influence of high strain rates on the behavior of quasi-brittle materials like concrete. It is based on gradient continuum damage, where the gradient part is extended with an inertia of damage. This causes a retardation of damage due to the fact that micro-cracks cannot spread out arbitrarily fast. The application is demonstrated with uniaxial tensile wave propagation and for a plane stress case. Increasing strain rates lead to an expansion of the linear stress–strain behavior with stresses exceeding the quasistatic material strength. 相似文献
996.
Circular tubes have been widely used as structural members in many engineering applications. Therefore, its collapse behavior has been studied for many decades, focusing on its energy absorption characteristics and collapse mechanism. In order to predict the collapse behavior of members, one could rely on the use of finite element codes or experiments. These tools are helpful and have high accuracy but are costly and require extensive running time. Therefore, an approximate model of tubes collapse mechanism is an alternative especially for the early step of design. This paper is also aimed to develop a closed-form solution to predict the moment–rotation response of circular tube subjected to pure bending. The model was derived based on the principle of energy rate conservation. The collapse mechanism was divided into three phases. New analytical model of ovalisation plateau in phase 2 was derived to determine the ultimate moment. In phase 3, the Elchalakani et al. model [Int. J. Mech. Sci. 2002; 44:1117–1143] was developed to include the rate of energy dissipation on rolling hinge in the circumferential direction. The 3-D geometrical collapse mechanism was analyzed by adding the oblique hinge lines along the longitudinal tube within the length of the plastically deformed zone. Then, the rates of internal energy dissipation were calculated for each of the hinge lines which were defined in terms of velocity field. Inextensional deformation and perfect plastic material behavior were assumed in the derivation of deformation energy rate. In order to compare, the experiment was conducted with a number of tubes having various D/t ratios. Good agreement was found between the theoretical prediction and experimental results. 相似文献
997.
U. Shumlak J. M. Blakely B.-J. Chan R. P. Golingo S. D. Knecht B. A. Nelson R. J. Oberto M. R. Sybouts G. V. Vogman D. J. Den Hartog 《Journal of Fusion Energy》2009,28(2):208-211
The ZaP flow Z-pinch experiment at the University of Washington investigates the innovative plasma confinement concept of
using sheared flows to stabilize an otherwise unstable configuration. The ZaP experiment generates an axially flowing Z-pinch
that is 1 m long with a 1 cm radius with a coaxial accelerator coupled to a pinch assembly chamber. Magnetic probes measure
the fluctuation levels of the azimuthal modes m = 1, 2, and 3. After assembly, the plasma is magnetically confined for an extended quiescent period where the mode activity
is significantly reduced. Experimental measurements show a sheared flow profile that is coincident with the low magnetic fluctuations
during the quiescent period. Recent experimental modifications produce more energetic Z-pinch plasmas that exhibit the same
general behavior. The plasma equilibrium is characterized with a suite of diagnostics that measure the plasma density, magnetic
field, ion and electron temperatures, in addition to plasma flow. The equilibrium is shown to satisfy radial force balance. 相似文献
998.
Singh S. Ziliotto F. Madhow U. Belding E. Rodwell M. 《Selected Areas in Communications, IEEE Journal on》2009,27(8):1400-1413
We present a cross-layer modeling and design approach for multigigabit indoor wireless personal area networks (WPANs) utilizing the unlicensed millimeter (mm) wave spectrum in the 60 GHz band. Our approach accounts for the following two characteristics that sharply distinguish mm wave networking from that at lower carrier frequencies. First, mm wave links are inherently directional: directivity is required to overcome the higher path loss at smaller wavelengths, and it is feasible with compact, low-cost circuit board antenna arrays. Second, indoor mm wave links are highly susceptible to blockage because of the limited ability to diffract around obstacles such as the human body and furniture. We develop a diffraction-based model to determine network link connectivity as a function of the locations of stationary and moving obstacles. For a centralized WPAN controlled by an access point, it is shown that multihop communication, with the introduction of a small number of relay nodes, is effective in maintaining network connectivity in scenarios where single-hop communication would suffer unacceptable outages. The proposed multihop MAC protocol accounts for the fact that every link in the WPAN is highly directional, and is shown, using packet level simulations, to maintain high network utilization with low overhead. 相似文献
999.
A. N. Georgobiani A. E. Atamuratov U. A. Aminov T. A. Atamuratov 《Inorganic Materials》2009,45(8):900-904
We model the formation of a nanoscale potential well with quantum wires on the semiconductor surface near the SiO2/Si interface owing to a special charge distribution in the oxide. We consider an SiO2/Si structure in the form of a cylindrical substrate covered with a coaxial oxide layer. The charge distribution in the oxide is taken to have the form of charged circular rings of finite thickness, coaxial with the cylindrical substrate. The parameters of the quantum wires are analyzed in relation to the charge distribution and density. Reducing the separation between two charged rings decreases the width of the quantum wires produced on the semiconductor surface and increases their depth. 相似文献
1000.