Abstract: To investigate the meso-damage evolution characteristic of unloading rock mass,unloading confining pressure tests on marble specimens were first conducted under initial confining pressures of 10,20 and 30 MPa. Then nuclear magnetic resonance tests were performed on the unloaded specimens. The stress-strain curves,transverse relaxation time T2 distribution,rock porosity,and nuclear magnetic resonance imaging pictures of the unloaded specimens were obtained. It is found that the deformation of the unloaded specimens changes from elastic to plastic with the increase of unloading confining pressure ratio. As the unloading confining pressure ratio increases,the size of small microcracks increases,and the number and size of large microcracks also increase. When the unloading confining pressure ratio is less than 90%,the damage of rock mass is mainly caused by the increase in number of microcracks.But when the unloading confining pressure ratio exceeds 90%,the damage of rock mass is caused by the sharp increase in number and size of microcracks. The rock porosity increases with the increase of unloading confining pressure ratio,and the growth rate becomes greater. The development processes of the number,size and structure of microcracks in the rock specimens under different initial confining pressures and different unloading confining pressure ratios can be directly visualized by nuclear magnetic resonance imaging pictures.
Abstract: A reasonable method was discussed for choosing and applying stiffness parameters in a 3D distinct element code. The formulas of pre-peak shear stiffness and normal stiffness of the fracture were derived through theoretical analysis. In combination with data from indoor shearing experiment,a corrected Bandis empirical formula of shear stiffness and a normal stiffness empirical formula were developed,which were proved to be logical by numerical analytical study. At last,a reality engineering of slope slide was discussed as a further evidence to describe the applicability of stiffness parameters chosen by the method mentioned above. It is obvious that the stiffness parameters of the fracture are a function of stress whether shear stiffness or normal stiffness. The corrected Bandis empirical formula can reflect the behavior of shear stiffness in the pre-peak range well. It is practicable to make the stiffness of the fracture changed with stress by developing a FISH program(in 3DEC),and therefore,the simulation can more in line with the practical engineering. In conclusion,the method mentioned above is proved to be reasonable.
Abstract: A discrete element model of a banana screen was established based on the 3D discrete element method. Virtual experiments were performed on difficult-screening particles with 0.8 times the diameter of the screen aperture,and the particle distribution under the state of particle stratification and penetration was obtained. The dependences of the screening effect of the model upon the screen inclination angle,vibrating angle and vibrating intensity were also discussed. As the vibrating intensity increases,the screening efficiency and the screening completion time decrease. When the screen inclination angle is 0.5°,the vibrating angle is 45° and the vibrating intensity is 3.5,the screen has the best screening effect,in which the screening efficiency is 92.2% and the screening complete time is 9.95 s.
Abstract: The density functional theory(DFT) was applied to investigate the geometric and electronic properties of a series of xanthate collectors. The reactivity of xanthate collectors was analyzed by using the highest occupied molecular orbital(HOMO) energy,natural population analysis charge,electronegativity and hardness index. It is found that xanthate anions are the active ingredient in flotation solutions,and the bonding atom of a xanthate anion is the S atom in the C-S bond. The HOMO energy can be used to interpret that the flotation activity of straight chain xanthates(C1-C6) increases with the alkyl chain growth. The more the branched chains of carbon atoms attached to polar groups in xanthate isomers,the stronger the flotation activity is. The order of the flotation activity of C3-C5 xanthate isomers is as follows:tert-alkyl xanthate sec-alkyl xanthate iso-alkyl xanthate.
Abstract: The effects of reductants and additives on the grain growth of metallic iron were investigated during the direct reduction of vanadium-bearing titanomagnetite concentrates. It is found that both the particle size and the vanadium content of metallic iron in reduced samples considerably increases as the reduction temperature rises. In comparison with a reduced sample using anthracite or lignite as a reductant,the particle size of metallic iron in a reduced sample using bitumite as a reductant considerably increases. This may be attributed to the high ash content of bitumite. A further study on the mechanism of the grain growth of metallic iron shows that Na2CO3 and Na2SiO3,with low melting points,decompose the structures of fayalite and hercynite and generate some low-melting-point phases,while SiO2 react with fayalite and form eutectic mixtures. These substances with low melting points can improve the diffusion of metallic iron in reduced samples and facilitate the grain growth of metallic iron.
Abstract: The influences of temperature and alkali metals on the gasification reactions of 5 kinds of stamp charging cokes were investigated by simulating the real conditions of blast furnaces. The carbon solution loss reaction regularity of the cokes was also analyzed by testing the optical textures and microscopic pore structures. The results show that the mass loss ratio of the cokes can increase quickly by rising the reaction temperature or enriching alkalis. Without alkalis,the mass loss ratio of the cokes increases slowly firstly and then quickly,and it is low when below 1000℃; but with alkalis,the mass loss ratio of 4 kinds of stamp charging cokes increases quickly firstly and gently then,and it reaches the maximum at 1100℃. The cokes contain more closed pores,more small pores,less large pores,and a few cecum-like pores locally. The quantity of large pores and connected pores in the cokes increases after the reactions. Except stamp charging coke A,whose coke reactivity index is the lowest,the other 4 kinds of stamp charging cokes are mainly basic anisotropic and coarse mosaic structures,which are less resistant to alkali metals at 1000℃ and 1100℃.
Abstract: A thermodynamic model of the phosphorus distribution ratio(LP) of CaO-MgO-FeO-Fe2O3-SiO2 steelmaking slags was developed based on the ion and molecule coexistence theory(IMCT) of slags and verified by experimental data. The predicted phosphorus distribution ratio of CaO-MgO-FeO-Fe2O3-SiO2 steelmaking slags in a temperature range of 1823 to 1873 K by the developed IMCT-LPmodel is more accurate than the measured as well as the predicted phosphorus distribution by other phosphorus distribution models. The developed IMCT-LPmodel can calculate not only the total phosphorus distribution of the slags but also the respective phosphorus distribution of ion pairs(Ca2+ + O2-),(Mg2+ + O2-),and(Fe2++ O2-) in the slags.
Abstract: The calcium treatment effect,the intermediate product formation and the modification routes of alumina inclusions by different intermediate products after calcium treatment were investigated by observing the shape and composition of these inclusions. It is found that blocky or rectangular solid inclusions finally change into spherical liquid inclusions,but their modification degrees are different. According to thermodynamic analysis,the higher the Als and S concentration in molten steel,the more difficult the modification of alumina inclusions is. Ca S and CaO exist as intermediate products in a short time after calcium treatment. A kinetic model of intermediate product formation shows that the critical[S] mass fraction of the formation of different intermediate products is 11.1×10-6 with 4×10-6 of dissolved oxygen. The modification routes of alumina inclusions by different intermediate products can be derived from the above model and experimental results.
Abstract: Non-slag decarburization of high-carbon ferrochrome can avoid toxic chromium slag emissions. Solid phase decarburization of high-carbon ferrochrome powder containing a certain proportion of calcium carbonate powder can be achieved using the characteristics of rapid heating powder materials in a microwave field. Experimental results show that adding a certain proportion of calcium carbonate powder does not affect the microwave heating characteristics of high-carbon ferrochrome powder. Deep decarburization of high-carbon ferrochrome powder is realized at a higher decarburization molar ratio of the mixed materials,a higher decarburization temperature,and a longer decarburization time,but the oxidation degree of decarburized ferrochrome powder is also increased accordingly. Under the suitable solid-phase decarburization conditions of the carburization molar ratio of 1:1.0-1:1.4,the microwave heating temperature of 1100℃ and the decarburization time of 60 min,the mass content of carbon in the decarburized materials is 3.91% to 1.71%,and the decarburization rate is 52.08% to 79.04%.
Abstract: To develop a real-time mathematical model which can be valid ever at a transient state for simulating full continuous casting processes,a real-time simulation mathematical model of heat transfer and fluid flow was constructed considering turbulent flow on the basis of the arbitrary Lagrangian-Eulerian(ALE) algorithm and the Lam-Bremhorst low-Reynolds number k-ε formulation. By using this model,dynamic grids expansion under moving computational domains could be realized and the temperature field and fluid flow field could be simulated for the full process of steel continuous casting. As an example,the simulation results of X70 steel are in accordance with experimental measurements.
Abstract: Microstructure and texture evolution in warm rolled Fe-6.5% Si alloy sheet were observed in the process of annealing treatment by means of electron backscatter diffraction,and the recrystallization behavior was discussed. The results show that the texture of the warm rolled and annealed sheet is composed of strong(111) 〈112〉,weak 〈110〉//RD and Goss. 〈110〉//RD and(111) 〈112〉recrystallized grains prior nucleate at the vicinity of grain boundaries of deformed grains possessing analogous orientation,thus low angle grain boundaries appear between recrystallized and deformed grains. New grains with statistic orientation and nucleated at sharp corners and places characterized by inhomogeneous microstructure form high angle grain boundaries with the surrounding matrix. Finally,(111) 〈112〉grains accumulated in the deformed matrix develop into(111) 〈112〉new grains,and the recrystallized(111) 〈112〉texture is strengthened. It is concluded that the annealing of the warm rolled sheet is characterized by low storage energy drive and inhomogeneous microstructure.(111) 〈112〉and(112) 〈110〉 deformed grains develop into new grains by continuous recrystallization. New grains formed in sharp corners are gained by discontinuous recrystallization,and their statistic orientation and high migration rate of high angle grain boundaries lead to a weakened texture level of recrystallization microstructure. In addition,Goss grains major nucleate in(111) 〈112〉deformed grains.
Abstract: The effects of annealing temperature on the microstructure,strength,elongation and anisotropy properties of cold-rolled 430 stainless steel were studied by continuous annealing experiment. An available double-heating section annealing process is obtained for the cold-rolled steel as the following:the intermediate and the maximum annealing temperature are 600 and 840℃,respectively,and the heating rate of the second heating section is maintained at 2.3℃·s-1. As continuous annealing proceeds,the mechanical properties of the strip have great changes:when the annealing temperature rises,the yield strength and hardness decrease by a two-stage trend,the elongation sigmoidally increases,the mean Lankford value remains at a level of approximately 1.25,and the variation of Lankford value on the rolling plane has apparent decrease. Quantitative relationships between yield strength and softening fraction and between yield strength and elongation are determined for the cold-rolled steel.
Abstract: 4A molecular sieves were successfully synthesized from the leaching solutions of fused titanium-containing electric furnace molten slag by using the reflux method and the hydrothermal method,respectively. The effects of H2O/Na2O mole ratio,reaction time,and temperature on the crystal phase and microstructure of 4A molecular sieves were systematically investigated when keeping the SiO2/Al2O3 mole ratio at 2. It is indicated that a 4A molecular sieve with well crystallinity and uniform size can be obtained by using the reflux method when the H2O/Na2O mole ratio is controlled at 80 and the reaction time is 8 h. Meanwhile,by using the hydrothermal method,a 4A molecular sieve can also be successfully prepared when the reaction is controlled at 120℃ only for 3 h. The adsorption properties for Cu2+ by 4A molecular sieves obtained at different temperatures were studied. The optimum adsorption efficiency of 70% is gained for a 4A molecular sieve synthesized at 120℃ for 150 min.
Abstract: The LiF-NaF and LiF-KF binary molten salt systems were assessed initially based upon the CALPHAD approach. The liquid and solid solution Halite phases were thermodynamically modeled by the substitutional solution model with Redlich-Kister polynomial terms. The model parameters were optimized by selected experimental phase equilibria information,thermochemical data,and present predicted data from the first-principles calculation. Whereafter,the thermodynamic database of the LiF-NaF-KF ternary system was established from the present assessed LiF-NaF and LiF-KF systems combined with the reported NaF-KF system through the Muggianu model with ternary interacting parameters optimized by the measured ternary eutectic point. It is demonstrated that the calculated results are well consistent with most of the experimental data and predicted data,which shows that the present thermodynamic parameters are credible and self-consistent and can allow accurate description of the phase equilibria and thermodynamic properties.
Abstract: The structure characteristic of the double damping system in a hydraulic rock drill was analyzed. The static balance position of the damping piston was determined by using the orifice flow law. The rebound velocity of the damping piston was derived from the transmitting principle of stress waves. The pressure equation of the 1st order damping chamber was deduced by considering the compressibility of hydraulic oil. The pressure of the 2nd order damping chamber was gained according to the equation of clearance flow rate. The motion differential equation of the damping piston was established based on these above foundations. The dynamic characteristics of the double damping system were simulated in Matlab. The movement laws of the damping piston were analyzed in different annular clearances. The relationships between annular clearance and the pressure in the 1st order and 2nd order damping chambers were discussed. The clearance-stroke coefficient was proposed,which was related to the ratio of annular clearance to maximum damping piston stroke. Simulation results show that the clearance-stroke coefficient is closely related to the damping system characteristics and has an optimal range. The mathematical model of the damping system was verified on the test platform.
Abstract: A whole life cycle model covering steel production,manufacturing,consumption and end-of-life,together with an output prediction model on the basis of per capita steel stock,is constructed to accurately forecast the trends of production routes,energy consumption and emissions for Chinese steel industry. Predictions with five scenarios including business as usual scenario,scrap recycle rate improvement scenario,steel lifetime improvement scenario,energy intensity improvement scenario and ALL scenario were conducted in combination with the analysis of energy use and CO2 emissions of each production unit. The results show that Chinese steel production,energy consumption and CO2 emissions will decline after a peak and the EAF production route will become the mainstream after replacing the BF-BOF route gradually. Meanwhile,production route change is the key "dividend"to cut the future energy consumption and emissions. The role of technical improvement will gradually emerge in the latter. To meet the goal of reducing emissions by half in 2050,many strategies,referring to ALL scenario,should be applied to promote the production route adjustment,steel recyclability and technologies of energy conservation and emission reduction.
Abstract: To solve the instability of multiple-factor regression models and the existence of over-learning and local minima of neural network models in predicting PM2.5 mass concentration,a method was proposed by combining support vector machine with fuzzy granulation of time series to predict the variation trend and range of PM2.5 mass concentration. According to the daily periodic variation of PM2.5 in different seasons,a 24-h pattern was determined to be the window length of granulating. Feature extraction of data samples proceeded by a triangular membership function was applied to support vector machine inputs for regressive modeling,and the optimum parameters of models were selected by grid search based on k-fold cross validation. Then a time series prediction model was established by using 1-h PM2.5 mass concentration obtained by Wanliu monitoring station at Haidian district of Beijing in 4 seasons from March 2013 to February 2014,and its resolving was realized by LIBSVM tool in MATLAB platform. The results show that the prediction model of PM2.5 mass concentration based on fuzzy granulation of time series can solve the instability caused by uncertain factors in mechanism modeling and get a good fitting effect on fuzzy granulation parameters.
Abstract: Existing density-based data stream clustering algorithms are difficult to discover clusters with different densities and to distinguish clusters with bridges and the outliers. A novel stream clustering algorithm was proposed based on the shared nearest neighbor density. In this algorithm, the shared nearest neighbor density was defined based on the shared nearest neighbor graph, which considered the degree of data object surrounded by the nearest neighbors and the degree of data object demanded by around data objects. So the clustering result was not influenced by the density variation. The average distance of data object and the cluster density were defined to identify outliers and clusters with bridges. The updating algorithm over the sliding window was designed to maintain the renewal of clusters on the shared nearest neighbor graph. Theoretical analysis and experimental results demonstrate the performance of clustering effect and a better clustering quality.
Abstract: An extrme learning machine(ELM) algorithm based on wavelet transform was designed for a class of indentification and regression problem with inhomogeneity in a space. From the standpoint of multiresolution analysis,a set of compactly supported orthogonal wavelets was constructed as the hidden layer activation function,and the output layer weight of the network was trained by an error minimized extreme learning machine. This method avoided retraining the output layer parameter as adding a subnetwork with higher resolution. The wavelet ELM was then extended into a two-dimensional space using the tensor product of a scaling function. To hurdle high-dimensionality issues,ridgelet transform based on ELM was obtained,whose scaling,direction,and position parameters were determined by optimization methods. Simulation results on functions with singularity confirm that the wavelet ELM can approch the target better. When being tested on some real benchmark problems,the ridgelet ELM demonstrates better training and testing accuracy on most cases.
Abstract: Based on the elasticity similitude law,three scaled models,including a frame structure with rigid foundation(RF),soil-structure interaction(SSI) with only one structure and structure-soil-structure interaction(SSSI),were constructed to investigate the effects of neighborhood structures on the dynamic characteristics of the soil-structure system. Then,the impulse excitation method was used to identify the frequencies,mode shapes,and damping ratios of the three models. All of the identified parameters were compared with those of prototypes by the finite element method. Test and numerical results show that there are two natural modes of SSSI,whose frequencies are close but phases are opposite corresponding to each mode of SSI. Moreover,the natural frequency of SSI will be in the interval of the corresponding two frequencies of SSSI. The vertical and rocking displacements increase in the SSSI system due to the effects of neighborhood structures. The scale factors of frequencies between prototypes and models agree with the similitude law.
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
