Abstract: The space-time distribution of microseismic activities in a mine was analyzed by minimum distance clustering. Combined with mining activities, areas with ground pressure activities were identified effectively. The time series curves of microseismic parameters were established to study the stress and deformation of local surrounding rock and investigate the precursor of rock mass failure. It is found that accumulation areas are isolated and unaffected each others, showing that large-area ground pressure activities will not happen. An abrupt increase of accumulated events number and energy after quiet in the time series curves represents the sudden release of accumulation energy in rock mass, indicating that the stability of surrounding rock deteriorates. Based on the research results and microseismic monitoring technology, a general model was established to study the stability of surrounding rock.
Abstract: Based on a lot of mining experiments, a representative blasting engineering was studied by three-dimensional numerical simulation. A numerical computational model of coal-rock media was constructed for the through strata blasting. Effective stress changes at different locations with time were acquired, and the difference in the decrease of effective stress with increasing distance was analyzed in different gas draining holes. Numerical simulation results show that the maximum radius of the area ruptured is up to 1.4 and 1.8 m for the top and bottom of the hole in the multi-media, respectively. The average value of effective stress in the bottom of the hole is 73% higher than that in the top at the same distance due to stress wave interference and reflection in the bottom of the hole. The blasting effect for a coal seam in the multi-media is better than that in a single coal seam. Under the same condition, the maximum value of the effective stress at the top and bottom of the hole in the multi-media is 17% to 42% and 6% to 24% higher than that in a single coal seam, respectively.
Abstract: Experiments on treating high-concentrated refractory organic wastewater from banknote printing works by organo-modified bentonite were performed to degrade the organic pollutants and color. The most important factor in the experiments is the dosage of poly aluminum chloride (PAC). When the dosages of organo-modified bentonite and PAC are 15 and 3. 5 g·L-1, respectively, and the mixing time is 0. 5 h, the treatment effect achieves the best level. The absorbance removal rate of the wastewater can reach up to 98. 11%, while the removal rate of chemical oxygen demand (COD) increases to 73. 31%. This treatment can dissolve COD and color in the wastewater without producing the concentrated wastewater and inviting any toxic and harmful substances, so it is a favorable pretreatment for an advanced wastewater treatment.
Abstract: Iron enrichment from refractory low-grade hematite was studied by using the method of direct reduction roasting in a tunnel kiln and magnetic separation. This study focused on the function and the mechanism of the assistant reducer NCP. Under the conditions of coal as the reducer with a mass fraction of 20%, CCO and NCP as the assistant reducers with mass fractions of 15% and 5% respectively, and roasting at 1 200℃ for 8 h, a concentrate of the Fe grade of 92. 61% with the Fe recovery of 92. 38% can be produced. The mechanisms of NCP were also investigated by X-ray diffraction and scanning electron microscopy. It is shown that NCP can react with quartz in the raw ore and generate natrosilite and albite, which can destroy the structure of the raw ore and induce a reaction between reducing gas and hematite to create Fe.
Abstract: A microwave assisted hydrothermal leaching method was used to extract nickel and cobalt from saprolite laterite. The effects of roasting pretreatment, leaching temperature and time on the extraction ratios of nickel and cobalt were investigated in detail. The extraction ratio of 93. 65% for nickel and 87. 86% for cobalt can be obtained respectively when the leaching temperature and time are 50℃ and 1 h for saprolite laterite only pre-roasted at 300℃. Comparing the microwave assisted hydrothermal leaching method with a hydrothermal leaching method, nickel and cobalt can be extracted more efficiently from the laterite. The experimental data indicate that the leaching process of nickel and cobalt is a diffusion-controlled process.
Abstract: To determine the formation and transformation behavior of retained ferrite in AISI304 austenitic stainless steel strips during the solidification process, the characteristic of retained ferrite and the solidification microstructure in the steel strips were studied by color metallography, electro-etching, electron backscatter diffraction and X-ray diffraction analysis. In the cast strips, there are three kinds of solidification structures:fine cellular crystals in the surface layer, equiaxed grains in the center, and columnar dendrites between them. The morphology of retained ferrite is rod-like in the fine cellular crystal zone in the surface, comb-like in the columnar dendrite zone, and curved branch in the equiaxed zone in the center. The mass fraction of retained ferrite in the cellular zone, the columnar dendrite zone, and the central equiaxed zone is about 4. 60% to 6. 60%, 3. 60% to 3. 70%, and 11. 27% to 11. 34%, respectively. The residual ferrite shows a W-shaped distribution in the thickness direction.
Abstract: The size, distribution characteristics, precipitation law, and composition of precipitate particles in ferrite matrix Ti-Mo micro-alloy steel with two different titanium contents were studied by metallographic microscopy, transmission electron microscopy and energy dispersive spectroscopy. Most of the precipitate particles are ultra fine carbides of less than 10 nm in size, and the particle sizes are a normal distribution. With the increase of titanium content from 0. 072% to 0. 092%, the average particle size increases and the distribution peak gradually moves to the particle size increasing direction. The Ti-Mo micro-alloy steel has an inter-phase precipitation style like ledge structures. The ledge spacing in the interior grain is different from that near the grain boundaries, and it is affected by cooling rate. Energy spectrum analysis shows that the Mo content is different in different sizes of particles. The composition of the bigger particles (about 50 nm) has no molybdenum, but the smaller particles (less than 20 nm) are compound of Ti and Mo. The Mo content increases with the particle size decreasing.
Abstract: To evaluate the stability of reversed austenite under the condition of stress and low temperature, the morphologies of reversed austenite in 9Ni steel after the treatments of quenching + tempering (QT) and quenching + lamellar quenching + tempering (QLT) were observed by transmission electron microscopy. Reversed austenite in the QT-treated sample is most lath-like; but in the QLT-treated sample, both thin foil and lath reversed austenite can be discovered and the former mainly turns up along lath martensite. The amount of reversed austenite and its carbon content before and after soaking in liquefied nitrogen were measured by X-ray diffraction. More stable reversed austenite is detected in the QLT-treated sample after soaking in liquefied nitrogen. The mechanical stability of reversed austenite was gauged by bending, uniaxial tensile and compression tests. Both the tensile and compress stress promote the reversed austenite to transform, and most of residual austenite are revealed within grains.
Abstract: Compared with E36 ocean platform steel, the microstructures and mechanical properties of three kinds of E690 ocean platform steels were studied as well as their corrosion behavior in simulating marine atmosphere. The corrosion rates during different periods were measured by the weight-loss method, the morphology and microstructure of the surface corrosion products were analyzed by scan electron microscopy and X-ray diffraction, and the grain boundaries were examined through electron backscattered diffraction. E690 platform steels consisting of bainite demonstrate outstanding mechanical properties and their impact values at-40℃ exceed 200 J. The majority of grain boundaries are sub-grain boundaries in a range from 3° to 15° and high angle grain boundaries surpassing 50°. The minimum corrosion rate of E690 ocean platform steels after 16 d is 0. 84 mm·a-1, which is far below 1. 4 mm·a-1 of ferrite + pearlite steels. The corrosion rates also tend to stabilize due to a compact rust layer. The rust layer consists of Fe3O4, α-FeOOH, β-FeOOH, γ-FeOOH and amorphous substances. It is revealed that the heat treatment and microstructure play an important role in the corrosion behavior during the earlier stage, but the chemical composition and density of the rust layer influence the corrosion behavior greatly in the later stage.
Abstract: Ultrasonic vibration effects on the microstructure and macro-segregation of 7050 aluminum alloy were investigated by adopting various ultrasonic powers to the aluminum melt. It is found that cavitation effect and acoustic streaming effect, caused by ultrasonic vibration, play a major role in the solidification process. A reasonable ultrasonic power can obviously refine the grains, optimize the microstructure, and improve the homogeneity of solute elements. The maximum decrease of the macro-segregation level occurs at the power of 170 W, and the segregation index values of Zn, Mg, and Cu are 0. 059 3, 0. 056 5, and 0. 031 9, respectively. Exceeding the power of 170 W, the rich level of solute elements in the ingot center enhances greatly and the macro-segregation level increases.
Abstract: The effect of heat treatment temperature on the microstructure transformation of the steel side in TA2-Q235B explosive clad plates was studied by optical microscopy (OM), electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM), and the formation mechanism was also analyzed. During the heat treatment process, the interface structure of the steel side decarburized, and a decarburized layer which is comprised of ferrite without structure characters formed. At 850℃ and below, the interface structure of the steel side near the swirl of the wave tip developed abnormally into big ferrite. At 900℃ and above, the interface structure of the steel side unusually grew into a columnar-structure ferrite structure. These aforesaid structures are influenced by both carbon diffusion and the phase transformation of matrix microstructure in the steel side. During the heat treatment process, TiC generated on the interface unevenly distributed on the interface, and locally accumulated on the interface with the increase of temperature, which accelerates the diffusion of carbon to the interface.
Abstract: Three kinds of ablation-resistant silicon fiber reinforced phenolic resin composite materials were compared in their weight lost rates, mechanical properties, macroscopic and microscopic morphologies after high temperature oxidation. It is found that the weight loss rates of the mixed braided composites are obviously higher than that of the single braided composite after high temperature oxidation. With increasing oxidation temperature the elastic moduli of both the mixed and single braided composites decrease. The single braided composite has the best ablation-resistant property among the three kinds of ablation-resistant silicon fiber reinforced phenolic resin composite materials.
Abstract: Blast furnace burden surface data derived from multi radars were processed. Fuzzy C-means and feature weighted fuzzy C-means clustering were applied to identify the burden surface data according to the data information, and a standard burden surface model database was set up. Each target burden surface was matched with the model database by using the method of nearness in fuzzy pattern recognition, and this provides a basis for the next burden surface control. The algorithm was carried out into a 2 500 m3 blast furnace, and the control effect has been improved. The simulation results show the effectiveness of the proposed method.
Abstract: In consideration of such problems as low gas utilization ratio, large gas consumption and high carbon dioxide emissions, a method was proposed by designing a new shaft furnace with oxygen injection into the upper zone. Based on the mass and energy balances of gas and solid phases, a static model of the shaft furnace was developed to simulate the iron-making process in the shaft furnace. Calculating results show that under the typical operation conditions, the gas volume of the shaft furnace with oxygen injection is 1 404. 67 m3, and the oxygen volume is 20. 32 m3 for per ton of direct reduction iron. In comparison with a traditional shaft furnace, the reduction potential of top gas decreases to 0. 56, the carbon emission decreases by 26. 25%, and the energy consumption decreases by 19. 56%.
Abstract: Deformations in the cathode and on the shell of aluminum reduction cells were systematically investigated in laboratory and industrial cells. The sodium expansion coefficient was obtained from test data. Numerical simulation was utilized to study the stress fields of the cathode and the shell, which took not only the sodium expansion chemical stress but also the temperature gradient thermal stress into account. The displacements of the shell during cell heating treatment and after start-up were acquired. The deformation on the shell of a 350 kA cell with the graphitized cathode has been monitored and measured for 360 d with a mechanical displacement meter. It is found that the simulation values are in good agreement with the measured ones.
Abstract: The forming mechanism of trapezoidal thread shafts was proposed by analyzing the forming process of teeth shape and the characteristic of metal flow. A die of cross wedge rolling was designed in consideration of the instantaneous variation of helix angle and the variation of teeth cross-section. The rolling process of trapezoidal thread shafts in cross wedge rolling was simulated with the finite element software Deform- 3D, and trapezoidal thread shafts with high precision were obtained. Radial and axial displacement variations in different sections of the rolled pieces were analyzed in detail by tracking multiple points on the rolled pieces using the tracking function of the finite element method. The metal flow law at different positions on the rolled piece was found out. The trapezoidal teeth profile rolled in rolling experiments performed by using the simulating parameters is similar to that calculated by the simulation software. Simulation and experiment results show that trapezoidal thread shafts with precise shape can be rolled by using the corresponding helix angle of the die to the instantaneous rolling radius.
Abstract: The structure of porous materials was reconstructed by using a Monte-Carlo method. It is verified that the reconstructed model has the fractal characteristics of self-similarity and scale-invariance. The reconstructed structure of porous materials was first meshed, and solid and fluid phases of the grids were identified by the binary theory. Then a series-parallel connection array model was established for the real heat transfer process. Finally a method of calculating the thermal conductivity of homogeneous and non-homogeneous porous materials, namely, the binary array method, was proposed. Closed-cell foam aluminum and alumina-silicate refractory fiber materials were taken as examples, and the binary array method was used to calculate their thermal conductivities. The calculated values fit well with experimental results respectively, proving the correctness and universality of the binary array method.
Abstract: This paper investigated the rates of diesel conversion and reforming over Ni-Yb/γ-Al2O3 catalyst (Ni 16%, Yb 5%) in low/high temperature diesel steam reforming with different inlet gases (CO2, H2 and CH4) as well as the influences of CO2 inlet gas on water-gas-shift and CO deep removal, which are the follow-up processes of the hydrogen production flowsheet based on diesel steam reforming for proton exchange membrane fuel cells (PEMFC). CO2 or H2 improves diesel conversion (> 95%) in low temperature (from 400 to 500℃) diesel steam reforming, which can let CH4 instead of diesel to participate high temperature (from 550 to 750℃) steam reforming, so that carbon deposition can be resisted obviously. However H2 shows depression on the high temperature steam reforming, and CH4 inlet gas depresses diesel conversion. When the molar ratio of gas to the total carbon of diesel is around 0. 54, CO2 inlet gas shows the best improvement on diesel conversion; however the CO content increases in the product gas, so the gas-hourlyspace-velocity of CO water-gas-shift should be reduced to reach the required CO removal ratio. There is no obvious influence on the two-stage methanation for CO deep removal.
Abstract: Differentiable and unconstrained quadratic programming can be constructed by improving a support vector machine (SVM) model using a smooth function, and thus a lot of fast optimization algorithms can be applied to solve the smooth SVM model. A new five-order spline function and a new seven-order spline function were constructed by a general three-moment method. These two spline functions are proved that their approximation accuracy is better than any other smooth functions, and the convergence accuracy of the spline function SVM model based on the five-order spline or seven-order spline is higher than any other smooth SVM models.
Abstract: A method for calculating the ductility reduction factor of a multi-degree-of-freedom system was proposed based on the capacity spectrum theory. The ductility reduction factors, overstrength factors, and strength reduction factors of 9 RC frames according to current Chinese seismic code with different heights and design seismic zones were calculated using the Pushover method. It is found that the structures with a higher design seismic level have a lower reserve strength when they have the same height, while the reserve strength will decrease with increasing height at the same design seismic level. The current Chinese seismic code was evaluated and some advices were proposed for its future modification.
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
