Abstract: For determining the mechanical parameters and failure mechanism of cemented sandstone, based on experiments, a micromechanical method based on 3-D particle flow code (PFC3D) was proposed to simulate the gradual failure process considering different particle stiffness ratios to verify the feasibility of the numerical model. The mechanical response of sandstone with different cemented materials was analyzed to further indicate the significance of cemented materials and the applicability of the numerical model. Considering changes in the particle stiffness ratio and the ratio of parallel bond stiffness to particle stiffness, the stress ratio, volume strain, coordination number and number of broken parallel bonds changing with axial strain were discussed and their influences on the Poisson's ratio, initial stiffness and ductility were deeply investigated for the cemented sandstone. Simulation results show that different stiffness ratios have different influences on the micromechanical response of the cemented sandstone. Especially with the decrease in particle stiffness, when the tangential stiffness is larger, the cemented sandstone is more brittle. The larger the ratio of parallel bond stiffness to particle stiffness, the greater the brittleness is, and shear failure is more prone to appear in the cemented sandstone. It is concluded that particle stiffness plays a significant role on the mechanical behavior and deformation ability of the cemented sandstone, and especially is very important to choose micro-parameters and construct a constitutive relation in 3-D numerical modeling for practical reservoir sandstone.
Abstract: This article is aimed at the three-dimensional visual simulation of water inrush in an underground mine. The topological properties of spatial relationships were presented based on the mining complex field theory and by analyzing the space geometry, distribution, vector property, and time sequence of field variables during a water inrush process. An integrated dynamic simulation model of water inrush in an underground mine was built and a visual simulation method of related attributes was put forward. After the voxel and field quantification treatment of spatial field variables, the dynamic flood spreading process was expressed visually by time step. With a typical underground mine as an example and through the analysis of relevant data, the dynamic visual simulation of water inrush in this underground mine was implemented and the model's feasibility and validity were tested and verified through this case study.
An ammonia-producing strain isolated from Inner Mongolia in north China, which is capable of decomposing urea, was designated as strain JAT-1. Identification results show that this milky strain has a smooth and humid surface, and it is Gram-negative and rod-shaped in φ0.2-0.4 μm×1.5-2.0 μm. Based on the 16S rDNA sequencing and the phylogenetic tree, this strain was identified as Providencia Sp. By means of the analysis of growth characteristics, the optimal growth condition was achieved when the concentration of sodium citrate as a carbon source was 10 g·L-1, the concentration of urea as a nitrogen source was 20 g·L-1, the pH value was between 8.0 and 9.5, and the inoculum concentration was 20%. Alkaline copper ore bioleaching experiment in a shake flask with the ammonia-producing strain yielded a copper leaching efficiency of 42.38% in 144 h. This result indicates that this strain has the potential for leaching the alkaline copper ore.
Abstract: Two types of nickel laterite ores were chosen as the object of study. Optical microscopy, scanning electron microscopy and X-ray diffraction were used to analyze the similarity and difference between the two ores. Both the ores were beneficiated by a selective reduction roasting-magnetic separation method for studying the influence of ore properties on direct reduction roasting. It is found that the main minerals, nickel-bearing minerals and nickel distribution are very similar in the two ores. But due to the difference in content of iron, silicon and magnesium, the beneficiation results using the selective reduction roasting- magnetic separation are quite different. This is probably the reason that in the roasting process, iron, magnesium and calcium cations react with silicate anions to form different silicates, affecting the melting properties of roasting ores and the reactivity of nickel.
Abstract: As an important production index in the present gold-mine beneficiation process, floatation recovery ratio is mainly ob-tained by laboratory test, which has long cycle time and is hard for the staff to control the flotation process standard. Based on massive actual production data, two prediction models of floatation recovery ratio for a gold mine were established respectively by using multiple linear regression and BP neural network method. By analyzing the predictive errors of the two models, it is approved that the prediction model based on BP neural networks can provide a better accuracy. When the relative prediction errors are within ±3%, the prediction accuracy reaches 91%, thus applying a good reference for practical production.
Abstract: The crystallization and evolution of non-metallic inclusions in CrMo drill pipe steel refined with a complex deoxidizer were investigated for the EAF-LF-VD-CC process flow of a domestic steel plant. As a result of aluminates floating, lower T[O] content in the steel before the LF refining was shown, while nitrogen content in the steel gradually increased during the whole flow. Large size inclusions (about 50 μm), namely, silicic manganates with low melting point, complexes with Na2O and magnesium aluminate spinels with a little CaO, appeared at the LF-VD stage and disappeared completely after the tundish process. Small size inclusions (< 10 μm) could be found during the whole refining flow. Their size at different refining stages was similar to each other, while smaller than that of the casting blank. The small size inclusions were complex oxides which consist of Mg, Al, Si, Ca and CaS respectively. The composition of the small size inclusions gradually moved to the liquid phase region during the smelting flow, and competition existed between CaO and MgO contents in these inclusions. Macro inclusions (> 100 μm) in the casting blank included complex inclusions caused by entrapped slag, MgO-CaO inclusions from refractories and endogenous aluminate inclusions coated by a CaS layer, whose composition was similar to small size inclusions in the smelting processes. The macro aluminate inclusions were easily broken into chain and further resulted in cracks in the steel during the rolling process. Hence, it is suggested to prolong the steel standing time after the VD operation to remove detrimental aluminate inclusions.
Abstract: Three heats of industrial trials were performed to investigate the cleanliness of A32 ship plate steel produced by a BOF-LF-RH-CC route. The variation of T. O and[N] contents as well as the transformation route and mechanism of inclusions in the steel were studied by system sampling during secondary refining processes. The steel have high level cleanliness with the T. O content under 2×10-5 and the[N] content under 4×10-5 in tundish samples. The T. O content, number density and average size of inclusions decrease during the LF refining process, and the inclusions transform into a CaO-MgO-Al2O3 ternary system. In the RH refining process, the T. O content and the number density of inclusions decrease, but the average size of inclusions increases. During calcium treatment, the number density of inclusions increases but the average size of inclusions decreases, and the inclusions transform into a CaO-Al2O3-CaS ternary system.
Abstract: Special TRIP steel with annealed martensite matrix (TAM steel) was produced by fully quenching and annealing in the two-phase region with the C- Si- Mn chemical composition of common TRIP steel. The microstructure and mechanical properties of TAM steel annealed at different temperatures were investigated by thermal dilatometry, tensile testing, optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. It is found that the microstructure of TAM steel consists of a uni-form fine annealed martensite matrix and an interlath second phase of retained austenite and bainite/martensite, which contribute to lowering the matrix's hardness and the strength ratio of matrix to second phase as well as decreasing the dislocation density. As the an-nealing temperature rises, the mixed blocky microstructure of newly formed martensite/bainite gradually increases, while the lath-like morphology of annealed martensite progressively disappears. Excellent mechanical properties are obtained when the annealing tempera-ture is 780℃, with the tensile strength, the elongation, and the product of strength and ductility up to 1130 MPa, 20%, and 22600 MPa·%, respectively. When the annealing temperature is relatively low, retained austenite mainly exists between annealed martensite laths in film-form and is conducive to the occurrence of TRIP effect.
Abstract: The chemical characteristics of trapped liquid and the corrosion features of X70 pipeline steel under a disbonded coating in a simulated solution of Kuerle soil were studied by using the rectangular stripping gap model. With the increasing of test time, the pH value of trapped solution gradually declines and finally reaches a stable level. Cl- has different degrees of gathering and its highest concentration occurs in the end of the gap. The concentration of SO42- decreases at the initial stage but increases at the late stage, the concentrations of HCO3- and NO3- decrease slightly from the holiday to the end, and the concentration change of cations is not obvious or only a minor reduction. The corrosion morphology of X70 steel under the disbonded coating performs obvious pitting corrosion, which is much more serious with the increasing of distance from the holiday.
Abstract: This article reports the solidification mode, microstructure, and element distribution of phases in 18Mn18CrN stainless steels with four kinds of N contents. N content significantly affects the solidification mode and microstructure of 18Mn18CrN alloy systems. The solidification mode of 18Mn18CrN stainless steels changes from Mode F to A as the N content increases from 0.07% to 0.72%. Additionally, the microstructure of 18Mn18CrN stainless steels changes from ferrite + austenite Widmanstätten dual-phase structure to ferrite + austenite dual-phase structure and a single phase of austenite as the N content increases. N content also affects the morphologies of austenitic phases. The lath-like or needle-like austenite phase changes into interdendritic and equiaxed austenite phases with the increase of N content. Ridges are present in interdendritic and equiaxed austenite grains, and the amount of ridges increases as the N content increases. There is a relationship between the ridges and the segregation of Cr, Mn and Fe elements in austenite phases during the solidification process. Moreover, this solidification segregation is retained to room temperature microstructure.
Abstract: The microstructure and mechanical properties of B1500HS laser tailor welded blanks before and after hardening heat treatment were studied by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, uniaxial tensile testing, and Vickers hardness testing. Before the heat treatment, the strength of the laser tailor welded blanks is much higher than that of the base metal, and the hardness is very unevenly distributed. After the heat treatment, the element distribution of the laser tailor welded blanks has almost no change, the overall strength is greatly improved, the plasticity greatly declines, the lateral plastic is the worst, and the hardness from the weld to base metal smoothly changes. This smooth transition of hardness makes the stress and strain distribution more uniform, ensures the good continuity of mechanical properties between the base material and the weld, and can significantly improve the formability of the laser tailor welded blanks.
Abstract: The precipitation behavior of nitride precipitates in grain-oriented silicon steel containing vanadium and titanium elements produced by thin slab casting and rolling process was studied by thermodynamic calculation and simulation experiment. The feasibility of nitride precipitates containing V and Ti elements as auxiliary inhibitors was also investigated. It is found that TiN is likely to precipitate at the final stage of solidification in the grain-oriented silicon steel, but VN and AlN can precipitate only in the two-phase region after solidification. Nitride precipitates in the grain-oriented silicon steel are mostly compound precipitates with complex chemical composition. Meanwhile, with increasing V and Ti contents, the distribution density of total inhibitors is significantly improved due to the increase in amount of nitride precipitates containing V and Ti elements. The inhibiting ability of inhibitors which restrain the normal growth of primary recrystallization grains is strengthened, and the magnetic induction value of final product is upgraded from 1.857 T to 1.898 T. Moreover, the addition amount of V and Ti, which is not more than 0.005% and 0.007%, respectively, does not affect the decarburization effect and the removal of S and N elements; the formed nano-sized nitride precipitates containing V and Ti elements are suitable as auxiliary inhibitors in the grain-oriented silicon steel produced by thin slab casting and rolling process.
Abstract: Fe78.3Cu0.6Nb2.6Si9.5B9 melt-spun ribbons of 6-8 mm in width and 30-40 μm in thickness were produced by using a single roller melt spinning technique machine. The melt-spun ribbons have the direct current (DC) magnetic properties of saturation flux Bs=1.06 T, remanence Br=0.39 T, coercivity Hc=3.53 A·m-1 and maximum permeability μm=2.43 mH·m-1 and the alternating current magnetic properties of core loss P0.5 T/1 kHz=22.2 W·kg-1, P0.2 T/100 kHz=864 W·kg-1 and corresponding efficient magnetic permeability μe=833 and 1225. Field emission high resolution scanning electron microscopy results indicate that the melt-spun ribbons prepared at different technical parameters show different crystallization degrees and fracture morphology characteristics. The fracture surface morphology of the amorphous-nanocrystallized ribbons is composed of a mirror zone, a mist zone, a hackle zone, and a river-pattern zone, while the crystallized ribbons exhibit intergranular embrittlement. The microhardness and elastic modulus of the amorphous-nanocrystallized ribbons measured with a nano-indenter probe are lower than those of the crystallized ribbons. The fracture toughness of the melt-spun ribbons was semi-quantitatively determined by using a self-designed gauge based on the Luborsky method.
Abstract: A synergistic effect of 1-hydroxybenzotriazole and sodium molybdate as corrosion inhibitors on copper in ASTM D 1384 simulated atmospheric corrosion solution was investigated by using electrochemistry, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Electrochemistry results revealed that BTAOH and Na2MoO4 compounding in 2 to 1, under the condition of a 50 mg×L-1 concentration, could improve the charge transfer resistance and reduce the corrosion current density, and the inhibition rate significantly reached to 90.7%. Corrosion products of copper in this simulated atmospheric corrosion solution piled up on the copper surface in an accumulative column shape; but the copper surface was smooth and dense in the corrosion inhibitor containing media, the hydrophobicity enhanced, and the surface contact angle significantly increased to 91.8°. X-ray photoelectron spectroscopy (XPS) results showed that Na2MoO4 transformed into MoO3 and MoO2 after interaction with copper, and two kinds of oxides padded in the gap of a surface film formed by BTAOH, which increased the density of the film and had good protective effect on copper.
Abstract: AA7050 alloy has a very high hot tearing and cold cracking tendency during direct-chill casting, which can affect its product quality and productivity, even cause industrial accidents. The trial and error method is often used in a foundry factory to find the optimum process parameters. However, this kind of approach is very costly and inefficient. Numerical modeling can reproduce the evolution of multi-physical fields in direct-chill casting, and it has been proved to be an indispensable tool in improving the casting process of aluminum alloys. In this paper, a direct-chill casting process of AA7050 alloy was simulated through direct coupling of thermal, fluid flow and stress fields. Simulation results showed that in the mushy zone the largest stress and strain components could be observed in the width direction, especially at the start-up phase. As a result, hot tearing perpendicular to the width direction was most likely to occur at this stage. The formation of cold cracking was closely related to stress concentration in the ingot, and the highest cold cracking tendency can be seen when the ingot was cooled to 200℃. According to the position of the cold crack in the ingot and the critical crack size needed, a speculation could be made that the cold crack was possibly caused by the further propagation of hot tearing at lower temperatures.
Abstract: The microstructure and phase components of as-cast and homogenized Al-Zn-Mg-Cu alloys with high strength and toughness were studied by combining thermodynamic calculation with experiments. It is found the secondary phases presented in as-cast alloy A are Mg(Zn,Al,Cu)2 and a small amount of Al2Cu; however, only Mg(Zn,Al,Cu)2 is found in as-cast alloy B. Thermodynamic calculation results show that the real solidification paths of alloys A and B fall between simulations by the Lever rule and the Scheil model, and the differences in content of phases in the two as-cast alloys are consistent with the regularity of the calculated mole fraction of phases formed after solidification in the Scheil model. Mg(Zn,Al,Cu)2 or Al2Cu phase in as-cast alloys A and B can be dissolved completely after conventional homogenization treatment (holding at 460℃ for 24 h), single α(Al) phase can be obtained, and this is consistent with the calculated isothermal section of the Al-Zn-Mg-Cu phase diagram with 7.5% Zn at 460℃.
Abstract: The spraying method, by which slurry preparation is simple, easy to operate and low cost, was applied to prepare photo-anodes for dye-sensitized solar cells. Nano-TiO2 thin films were prepared by a colloidal spray coating technique, and the spraying slurry mainly included tetra-n-butyl titanate (TBT) and P25. Ethylene glycol (EG) was selected as a pore-forming agent to investigate its optimum addition. Through analyzing the I-V curves of the cells, the roughness, dye adsorption amount and diffuse reflection spectra of the thin films, and the scanning electron microscopy images and electrochemical impedance spectra of the photo-anodes, we draw the following conclusions. When the ratio of EG to TBT is 1:1 by volume, the thin film reaches the largest surface area, the dye adsorption amount is 1.47×10-7 mol·cm-2, and the cell has the best performance with the open-circuit voltage of 0.69 V, the short circuit current of 13.0 mA·cm-2, and the photoelectric conversion efficiency of 5.38%. The photoelectric conversion efficiency is nearly two times that without the pore-forming agent, and now the electron transfer resistance is the least.
Abstract: Carbon samples were prepared from cellulose by carbonization under the nitrogen atmosphere and water steam activa-tion. Their structure and specific surface area during carbonation and activation processes were studied by thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, and nitrogen adsorption at low temperature. The results show that groups in the cellulose molecular structure like C-OH, C-O-C and C-H are mostly pyrolyzed completely between 280-380℃. A few fragments or surface groups produced during pyrolysis decompose continuously above 380℃. Meanwhile, carbon atoms rearrange within the solid sample and form graphite crystallites. Carbonization temperature exerts a crucial influence on the microcrystalline carbon structure and pore structure. With the rise of carbonation temperature, the size of graphite crystallites increases and the pore structure develops, but the specific surface area of the carbon prepared first increases and then decreases, reaching maximum at 600℃. Carbonization time has less significant influence on the structures. With increasing activation time, non-crystalline carbon is oxidized, the specific surface area and total pore volume of the carbon sample increase simultaneously. However, a longer activation time causes that the original crystalline carbon structure is destroyed, the specific surface area and total pore volume of the carbon sample decrease. The porosity is mostly abundant when non-crystalline carbon is fully oxidized and the original crystalline carbon structure is not destroyed.
Abstract: In order to solve the large wall temperature difference and high NOx emission of W-shaped radiant tubes, this article introduces a kind of W-shaped radiant tube with flue gas circulation. A mathematical model of the radiant tube is established and the radiant tube is studied by the method of numerical calculation. On the basis of the model's reliability, the velocity field, temperature field and NOx emission are compared between the radiant tube and a conventional W-shaped radiant tube. The average gas velocity of the new radiant tube is three times that of the conventional radiant tube, and 57.6% flue gas is involved in recombustion in the new radiant tube. The maximum combustion temperature of the new radiant tube is 2260 K, which is 192 K lower than that of the conventional radiant tube. The wall temperature difference of the new radiant tube is 166 K,which is 76 K lower than that of the conventional radiant tube. The NOx emission of the new radiant tube is 9.9×10-5, but the NOx emission of the conventional radiant tube is 7.98×10-4, nearly seven times higher.
Abstract: In order to solve the problem that the density clustering algorithm is sensitive to neighborhood parameters, this article introduces a density-based fuzzy adaptive clustering algorithm. Without predefined clustering number and neighborhood parameters, this algorithm adaptively determines the radius of neighborhood to obtain the density of each sample and increases cluster centers based on the density. A new validity measure for fuzzy clustering is proposed to choose the best clustering number so that the sensitivity of density clustering is eliminated. UCI benchmark data sets are used to compare the proposed algorithm and the traditional density clustering algorithm. Experiment results demonstrate that the proposed algorithm improves the clustering accuracy and the adaptability effectively.
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
