Abstract: The characteristic equations of micro forces such as van der Waals force, electrostatic force, steric type force and surface tension were established on the basis of the existing experiments and theories of micro flow. The effect of various micro forces on fluid flow in porous media was analyzed in detail. A mathematical model considering the effect of micro forces was constructed for fluid flow in micro tubes. A new relative permeability formula considering micro forces was derived using the capillary bundle model of porous media. Numerical analysis clarified the effect of micro forces on fluid flow in porous media. Simulation results show that micro forces cannot be neglected in micro-scale porous throats.
Abstract: Al2O3 and solid calcium aluminate were considered as un-reacted cores, the diffusion of aluminum cations in the liquid calcium aluminate layer was confirmed as the rate determining step of Al2O3 inclusion modification, and further a kinetic model of Al2O3 inclusion modification was established on the basis of the un-reacted core model. The model parameters were calculated by thermodynamic analysis. Modelling results show that the time of Al2O3 inclusion modification to completely liquid calcium aluminate will be much longer when the size of Al2O3 inclusions increases. Moreover, increasing the Ca content in a reasonable range is beneficial not only to modify Al2O3 inclusions to liquid calcium aluminate from thermodynamics but also to speed the modification process whereas the enhancement weakens when the Ca content exceeds a critical level. Temperature rise is disadvantageous to Al2O3 modification chemical reaction so the driving force of Al2O3 inclusion modification decreases correspondingly, namely temperature rise is not so obvious to speed Al2O3 inclusion modification. Finally, the kinetic model results were verified by industrial trials and they accord with each other very well.
Abstract: Under the Euler-Lagrange framework, based on the quantitative description of inclusion morphology using the fractal theory, the motion behavior of condensed Al2O3 inclusions in liquid steel in a continuous casting tundish was studied by numerical sim-ulation. It is found that liquid steel flow field and inclusion morphology influence the motion behavior of Al2O3 inclusions in liquid steel together. With increasing inclusion size, the floating removal rate of two different morphologies of inclusions, cluster-like Al2O3 inclu-sions and spherical Al2O3 inclusions, becomes larger gradually. At the same inclusion size, the floating removal rate of cluster-like Al2O3 inclusions is lower than that of spherical Al2O3 inclusions. As the inclusion size increases, the floating removal rate of cluster-like Al2O3 inclusions decreases more than that of spherical Al2O3 inclusions with the same size. At the inclusion size of 20, 40, 60 and 80μm, the floating removal rate of cluster-like Al2O3 inclusions decreases by 4.8%, 5.7%, 6.4% and 12.5% compared with spheri-cal Al2O3 inclusions, respectively.
Abstract: The effects of cooling rate on the strength and toughness of austenite decomposition products in high strength Cu-bearing steels HSLA80 and HSLA100 were investigated during continuous cooling. Characterization and ripening of Cu precipitates formed dur-ing continuous cooling were discussed. Continuous cooling experiments from 0.1 to 20℃·s-1 were carried out by Gleeble thermo-simu-lation. Microstructures and Cu precipitates were observed by scanning electron microscopy and transmission electron microscopy. It is found that the microstructure of austenite decomposition products in HSLA80 steel changes from polygonal ferrite to granular ferrite and bainite with increasing cooling rate. Cu precipitation occurs during continuous cooling within the cooling rate of 0.1 to 1℃·s-1. Due to the microstructure and Cu precipitates, the hardness changes by stages and the toughness increases gradually as the cooling rate in-creases. The microstructure of austenite decomposition products in HSLA100 steel is mainly bainite and Cu precipitation does not oc-cur, so that the hardness does not change on the whole, but the toughness varies dramatically with increasing cooling rate. Ripening of Cu precipitates formed during continuous cooling obeys the Ostwald law. The radius of Cu precipitates increases with aging time t1/3.
Abstract: The relation of the morphology of grains in 430 stainless steel with microstructural parameters, such as grain nucleation density, Gaussian decomposition parameters and Gibbs-Thomson coefficient, was studied based on the CAFE model. The effects of casting conditions, such as superheat and cooling intensity, on the solidification microstructure were also analyzed in this paper. It is found that the grain size and the columnar to equiaxed transition (CET) are both affected by maximum bulk nucleation undercooling and maximum nucleation density. As the Gaussian decomposition parameters and Gibbs-Thomson coefficient increase in an appropriate range, the primary dendrite arm space decreases, but the central equiaxed area increases. Besides, the central equiaxed area decreases with increasing superheat and cooling intensity, while the primary dendrite arm space shows no obvious change.
Abstract: The initial corrosion behaviors of pure copper and electroplating copper-clad steel in Dagang soil were investigated by burying tests in lab for 30 d, combining polarization curves, electrochemical impedance spectroscopy (EIS), and weight-loss method. It is found that during the initial stage of the corrosion process, the average corrosion rate of pure copper is slightly lower than that of electroplating copper-clad steel, and pure copper exhibits a higher corrosion resistance than electroplating copper-clad steel. There are some differences in the corrosion mechanism between pure copper and electroplating copper-clad steel. The corrosion behavior of pure copper is mainly affected by diffusion control.
Abstract: Based on the Gurson damage model, the thermal stamping formability of AZ31 magnesium alloy sheet was predicted by employing finite element simulation and thermal stamping test. Taking the plastic anisotropic behavior of the AZ31 sheet into account, the Gurson damage model was implemented in the commercial finite element software ABAQUS/Explicit by using the user material subroutine VUMAT. Parameters employed in the Gurson damage model were determined through uniaxial tensile test and numerical iterative computation. The evolvement and distribution of micro voids in the AZ31 sheet during thermal stamping were simulated by using ABAQUS. The internal damage evolution due to micro void growth and coalescence developed at different temperatures in the AZ31 sheet was observed by scanning electron microscopy. The predicted micro void distribution agrees well with experimental data. Therefore, this result indicates that the presented approach can be employed to predict the thermal stamping formability of metal sheet.
Abstract: Copper-based friction materials were made by powder metallurgy (P/M) from copper powder and ferrous powder, which is reduced Fe powder, spongy Fe powder, Fe-Ni alloy powder and Fe-Cr alloy powder, respectively. Their friction and wear properties were investigated by friction testing, scanning electron microscopy and microhardness measurement. When the rubbing speed increases from 3000 to 6200 r·min-1, the friction coefficient of specimens drops greatly. For specimens with spongy Fe powder, the friction coefficient changes less than 0.024, showing a stable friction coefficient but serious wear. When ferrous powder is strengthened by nickel, the friction coefficient stability of specimens at high rubbing speed improves obviously, and the friction coefficient changes less than 0.027. Specimens with Fe-Cr powder obtain the optimum wear resistance with almost constant wear rate as the rubbing speed increases.
Abstract: Nano Fe-Ni-Cr/SiC composite coatings were prepared by using a pulse electrodeposition method from trivalent chromium baths containing a compound carboxylate-urea system and SiC nanoparticles in ultrasonic fields. The influence of pulse electrodeposition and ultrasonic parameters on the SiC and Cr contents in the composite coatings and the coating thickness was investigated, and the effect of ultrasonicwaves on the electrochemical behavior of the composite coatings was analyzed by steady-state polarization curves and cyclic voltammetry (CV) curves. It is indicated that the SiC and Cr contents in the composite coatings and the coating thickness are significantly increased since both ultrasonic waves and pulse electrodeposition are favorable to the deposition of the matrix metals Fe, Ni and Cr. The surface morphology, phase composition and chemical composition of the composite coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The composite coating with a 23.56μm thickness, 4.1% SiC and 25.1% Cr was obtained by this technique. According to the measurements of weight loss and typical potentiodynamic polarization curves, the properties such as anti-wear and corrosion resistance could be improved by increasing the SiC content in the composite coatings.
Abstract: Ni60B nickel based alloy coatings and micro WC, nano WC and micro-nano WC particle reinforced Ni60B composite coatings were fabricated using laser cladding technology, hereinafter called as WCm, WCn and WCmn coatings,respectively. Sliding wear tests at different loads and sliding distances were conducted for the coatings using an Amsler200 tester under water lubrication conditions. The results show that the addition of WC particles can improve the wear resistance of Ni60B coatings and that the wear resistance of the WCm and WCn coatings does not presentan obvious difference, however their worn morphologiesare different. The wear resistance of the coatings is much better under water lubrication than dry sliding wear because the water lubrication film can play a support or isolating action between the coatings and the wear wheel, which decreases their contact stress, and because water cooling to friction couples decreases the temperature rising and the softening of the coatings. W element which is saturated in the WCn and WCm-coatings diffuses and agglomeratesduring water lubrication wear.
Abstract: SiC particles reinforced Al matrix composites with three different SiC volume fractions of 40%, 56% and 63% for electronic packaging were prepared by pseudo-semi-solid thixoforming. The Al and SiC distribution and the fractographs of the SiCp/Al electronic packaging materials were examined by optical microscopy and scanning electron microscopy. The density, relative density, thermal conductivity (TC), coefficient of thermal expansion (CTE), compressive strength and bending strength of the SiCp/Al electronic packaging materials were tested. It is found that the SiCp/Al electronic packaging materials have controllable coefficients of thermal expansion and high relative density. The Al matrix is connected into a network, and SiC particles are uniformly distributed in the Al matrix. When the SiC volume fraction increases, the density and thermal conductivity at room temperature lightly increase, the coefficient of thermal expansion gradually decreases, and the compressive strength and bending strength increase. The main fracture mode of the SiC/Al electronic packaging materials is brittle fracture of SiC particles accompanied by ductile fracture of the Al matrix at the same time.
Abstract: Potassium titanate (K2Ti6O13) nanowhiskers were successfully prepared from electric furnace molten slag with titanium by a hydrothermal method with alkaline solution, then refluxing in an acid medium and finally calcination. The effects of titanium-to-potassium mole ratio, calcination temperature, reaction time and water immersion on the crystal phase and morphology of as-prepared products during the calcination process were investigated in detail by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray fluorescence. It is found that one-dimensional single crystalline metatitanic acid nanorods with uniform size are obtained when the hydrothermal reaction is controlled at about 200℃ for 24 h in a 12 mol·L-1 potassium hydroxide solution. The purity, the crystallinity degree and the aspect ratio of formed potassium titanate whiskers are improved with increasing titanium-to-potassium mole ratio from 1.50 to 1.75, calcination temperature from 800 to 1100℃, and reaction time from 0.5 to 7 h. The optimum conditions for preparing potassium titanate nanowhiskers are the titanium-to-potassium mole ratio of 1.75, the calcination temperature of 1100℃, the reaction time of 5 h, and the water immersion time of 2 h.
Abstract: Aiming at the difficulty of predicting blast furnace hanging, a prediction method was proposed for the hanging based on the D-S evidence theory and in combination with fuzzy expert inference and a posterior probability least squares support vector machine. Firstly, the causes of hanging are obtained by mechanism analysis in consideration of blast furnace operations and hanging phenomena. Secondly, subjective evidences are extracted by fuzzy expert reasoning, while a posterior probability least squares support vector machine model is developed to extract objective evidences. Finally, in order to predict the hanging precisely, the subjective and objective evidences are fused based on the D-S evidence theory, which makes full use of the expertise and the self-learning ability of the least squares support vector machine. Simulation results illustrate that the proposed method can make accurate prediction of the hanging.
Abstract: The effects of the bottom shapes (well-bottom, flat-bottom and mountain-bottom) of submerged entry nozzles (SENs) and the well depth of well-bottom SENs (0, 10 and 20 mm) on the level characteristics of high-speed continuous casting molds were investigated by full scale water modeling and plant trials. Fluid flows in the molds with well-bottom and flat-bottom SENs are more symmetrical than those with mountain-bottom SENs. The decreasing order of meniscus velocity in the molds is from mountain-bottom, flat-bottom to well-bottom SENs. Comparative studies on the level characteristics of the molds between well-bottom SENs with different well depths show that well-bottom SENs with the well depth of 10 mm can decrease the level fluctuation and meniscus velocity, and this is helpful to prevent slag entrapment. Plant trials indicate that level fluctuation in the molds with mountain-bottom SENs is higher than that with well-bottom SENs, and this agrees well with the water modeling results. The power density spectra of level fluctuation using mountain-bottom SENs are about 10 times as large as those using well-bottom SENs at the frequency ranging from 0. 003 to 0. 05 Hz.
Abstract: This article introduces a method of extracting the typical defect vector of strip shape. In the method, firstly the strip shape defects are primarily classified, then the unit typical strip shape vector is extracted according to similarity among strip stresses, and finally the typical ratio coefficient is solved with the k-means cluster approach. Aiming at the unit typical strip shape vector extracted, a taper work roll was designed and put into a large-scale trial. It is shown that the shape quality of rolled strips is better than before. The comprehensive flatness is below 5 IU, and side and middle composite buckles are basically eliminated.
Abstract: An improved pressurization step with raffinate and vacuum exhaust step were developed and experimentally studied in a three-bed vacuum pressure-swing adsorption (VPSA) system with activated carbon for ventilation air methane (VAM) upgrading. It is found that pressurization with raffinate from the effluent end can prolong the penetration time and increase the CH4 concentration in product gas in the case of the same raffinate concentration;but the vacuum exhaust step can increase the CH4 concentration in product gas without increasing pressure. A three-bed VPSA cycle which contains the two steps was also studied experimentally. The results show that the CH4 concentration in product gas can increase from 0.4% to 0.654% with the CH4 recovery of 65% when the CH4 concentration in feed is 0.2% and the adsorption and desorption pressures are 140 kPa and 20 kPa, respectively.
Abstract: A bi-objective optimization model of rescue routes was built by using the operations research theory. An algorithm which suites to solve the model and has rapid convergence rate was proposed on the basis of heuristic algorithms. This algorithm calls the Dijkstra algorithm by constructing auxiliary functions, gradually approach optimal solutions in the approximate range of optimal solutions by multiple iterations and finally obtain the shortest path of the double-weighted network, therefore it is a fast, approximate algorithm. The specific steps of the algorithm were listed by analyzing the nature of auxiliary functions. The error and influence factors on the convergence rate were analyzed, and the time complexity and the advantages of the algorithm were also discussed. Finally, the algorithm was compiled and implemented in a specific case, and the results are proved to be consistent with theoretical conclusions.
Abstract: One crucial issue of service-based trustworthy application development is how to measure the trustworthiness of Web services. A comprehensive trustworthiness measurement model for Web services, TMM4WS, was proposed based on the unique features of Web services. The model measures the trustworthiness of a Web service in terms of both its source code and external usage. A tool called TMT4WS was developed to support the model. An empirical study was conducted on tens of Web services to validate the effectiveness of the model and its supporting tool. Experimental results show that the model and its supporting tool can be employed to provide a quantitative trustworthiness measurement of Web services.
Abstract: This paper introduces the design problem of optimal output regulators for multirate linear discrete-time descriptor causal systems. At first, by making use of the discrete lifting technique the original system is transformed into no state time-delay system in form. Then thought the equivalent transformation, taking advantage of the causal characteristics of the system, it is changed into a normal system. Continuing to apply discrete lifting into the system, a simple single-rate system in form is exported. The performance index function of the original system is modified to that of the single-rate system, and then an optimal output regulator is obtained by using the optimal regulator theory. Through transformation an optimal output regulator for the original system is finally derived. At meantime, the stabilizability and detectability of the exported single-rate system were discussed, and their rigorous mathematical proofs were given. Numerical simulations proved the effectiveness of the preview controller designed in this paper.
Abstract: The performance levels of frame structures and masonry-infilled walls together with corresponding inter-story drift limits were proposed by statistical analysis based on the current research results. A nonlinear finite element model was established for masonry-infilled frames. Nonlinear static analysis was performed for 6-,9-,and 12-story masonry-infilled frame structures under frequent, moderate and rare earthquakes and the inter-story drifts were obtained. According to the performance index, the seismic performances of masonry-infilled frames were evaluated and the inadequacy of the Chinese seismic code was pointed out. Based on the calculated results, a table for performance evaluation of masonry infilled frames is given for reference in practical use.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
