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221.
Aluminum–boron carbide particle reinforced composite is an advanced material which can be used in applications such as neutron-shielding
components, aircraft, and aerospace structures. In the microstructural characterization of an Al–7%Si–10%B4C die casting, attention is particularly focused on particle distribution and interface reaction products between B4C particles and the aluminum matrix. The quantitative analysis results show that, in a cross-section of the cast part, more
particles concentrate in the center and fewer particles are present in the wall regions. Moreover, some particle segregation
bands have been observed. The mechanisms of the particle migration are proposed to describe the phenomenon. However, the average
particle fraction in any cross-section of the cast part is almost the same. A barrier layer consisting of several sublayers
was detected on the surface of B4C particles. Using electron diffraction in selected areas, it is found that these sublayers are composed of Al3BC crystals, TiB2 crystals, Si crystals, and coarse stick-shaped TiB2 particles. In addition, it is observed that Si plays an important role in the formation of a dense barrier layer. The barrier
layer can limit B4C decomposition and improve B4C stability in the aluminum melt. 相似文献
222.
Wenying Wei Zhen Wang Yanhua Yin Jinyu Han Wen Xu 《Korean Journal of Chemical Engineering》2008,25(3):562-567
Composition Group Vector Space (CGVS) method for estimating melting and boiling point T
m
, T
b
of organic compound has been proposed, and the principle of this method has been elucidated. The models for estimating T
m
, T
b
have been established and the numerical values of relative parameters have been presented. The average percentage deviations
of T
m
, T
b
estimation are 7.53 and 1.58, respectively, which show that the present method demonstrates significant improvement in applicability
to predict the above properties, compared to conventional group methods. 相似文献
223.
224.
Khaled Chahine Mark Ballico John Reizes Jafar Madadnia 《International Journal of Thermophysics》2007,28(6):2118-2127
A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate
the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign
of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used
in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the
design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically
99.5–99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the
blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical
to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In
another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients.
In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions
within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and
thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly
including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile
up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement
was obtained. 相似文献
225.
Future of energy 总被引:1,自引:0,他引:1
John A. Glaser 《Clean Technologies and Environmental Policy》2007,9(3):157-161
226.
Treated was an anti-plane crack perpendicular to the interface of an exponential-type FGM strip bonded to another linear-type
FGM substrate with infinite thickness. Through Fourier integral transform, the problem was reduced as a Cauchy singular integral
equation, which was further solved numerically by the Lobatto–Chebyshev collocation method. Based on the numerical solution,
the effects of the geometrical and physical parameters on the stress intensity factor (SIF) were analyzed and the following
conclusions were obtained: (a) A notable discrepancy between the interface-perpendicular crack and the interfacial one is
that, to reduce the weak-discontinuity of interface or to make the interface micro-discontinuous will not necessarily decrease
the SIF of the former, but will surely decrease that of the latter. (b) When a crack tip is situated very near to the interface
(or free surface), its SIF will be high and totally dominated by the interface (or free surface). (c) To increase the stiffness
of the FGM on one side of the interface is beneficial to preventing the crack on the other side from growing toward the interface.
Besides, some practical suggestions were further given for material design in the field of composites. 相似文献
227.
228.
A new high-order accurate continuous Galerkin method for linear elastodynamics problems 总被引:1,自引:1,他引:0
Alexander V. Idesman 《Computational Mechanics》2007,40(2):261-279
A new high-order accurate time-continuous Galerkin (TCG) method for elastodynamics is suggested. The accuracy of the new implicit
TCG method is increased by a factor of two in comparison to that of the standard TCG method and is one order higher than the
accuracy of the standard time-discontinuous Galerkin (TDG) method at the same number of degrees of freedom. The new method
is unconditionally stable and has controllable numerical dissipation at high frequencies. An iterative predictor/multi-corrector
solver that includes the factorization of the effective mass matrix of the same dimension as that of the mass matrix for the
second-order methods is developed for the new TCG method. A new strategy combining numerical methods with small and large
numerical dissipation is developed for elastodynamics. Simple numerical tests show a significant reduction in the computation
time (by 5–25 times) for the new TCG method in comparison to that for second-order methods, and the suppression of spurious
high-frequency oscillations. 相似文献
229.
230.
Sangho Kim Young-Roc Im Sunghak Lee Hu-Chul Lee Sung-Joon Kim Jun Hwa Hong 《Metallurgical and Materials Transactions A》2004,35(7):2027-2037
This study is concerned with the effects of alloying elements on fracture toughness in the transition temperature region of
base metals and heat-affected zones (HAZs) of Mn-Mo-Ni low-alloy steels. Three kinds of steels whose compositions were varied
from the composition specification of SA 508 steel (grade 3) were fabricated by vacuum-induction melting and heat treatment,
and their fracture toughness was examined using an ASTM E1921 standard test method. In the steels that have decreased C and
increased Mo and Ni content, the number of fine M2C carbides was greatly increased and the number of coarse M3C carbides was decreased, thereby leading to the simultaneous improvement of tensile properties and fracture toughness. Brittle
martensite-austenite (M-A) constituents were also formed in these steels during cooling, but did not deteriorate fracture
toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated HAZs also had sufficient
impact toughness after postweld heat treatment. These findings indicated that the reduction in C content to inhibit the formation
of coarse cementite and to improve toughness and the increase in Mo and Ni to prevent the reduction in hardenability and to
precipitate fine M2C carbides were useful ways to improve simultaneously the tensile and fracture properties of the HAZs as well as the base
metals. 相似文献