Abstract: The disaster-causing mechanism of unstable tailing dams is extremely complex. However, the impact of multi-scale and multi-factor mechanical properties of railings is not adequately considered in existing studies on the disaster prevention of tailing dams, and the mechanism of the cataclysm of fine grained tailing dams and high piled tailing dams is not clear. Aiming at the basic and common problems existing in studies on the disaster-causing mechanism of tailing dam, this article collects a lot of documents closely related to tailing dam disaster at home and abroad, and briefly introduces the study status and results of the structural multi-scale characterization and mechanical characteristics of tailings, the deposition law of railings, the formation and structure of tailing dams, the stability analysis of tailing dams and the disaster-causing mechanism. On this basis, some existing shortcomings are pointed out in current researches, the key scientific problems in the related research fields of tailing dam disaster are extracted which have to be quickly solved, and finally, concrete and comprehensive analyses are conducted on the development direction in the future of the research.
Abstract: Under the ventilation condition of U + L, a crossheading has important impact on spontaneous combustion of residual coal in a gob area. In order to ensure mine safety and obtain parameters to prevent spontaneous combustion of residual coal, on the basis of the mechanism of coal oxidation and using UDF to incorporate the reaction mechanism into FLUENT, multi-field coupling numerical simulation was performed to study the distribution law of the oxidization and heat accumulation zone in a gob with a cross-heading. The results show that the air flow field, oxygen concentration field and temperature field all change when the crossheading exists, the oxidization and heat aeeumulation zone not only offsets to the return-side but also becomes deeper and wider. The distance between the erossheading and working surface affects the width of the oxidization and heat accumulation zone, and when it is 20 m, the maximum width is approximately 25 m. After 10 d of reaetion, the heating rate at the high temperature point can reach 1.24K·d-1 in the U + L ventilation system, which is 1.5 times that in the U ventilation system. However, the position of the crossheading has little effect on the high temperature point. The temperature nearby the crossheading is the highest in the return-side temperature field of the U + L ventilation system, and the average temperature is d K higher than the same location temperature in the U system per day. With increasing distance from the crossheading to working face, the heating rate in the crossheading rim increases from 0.1 K·d-1 to 0.9 K·d-1. Although the crossheading does not belong to the high temperature region in the whole temperature field, it has good warming potential.
Abstract: Tailing-cemented backfill is a cement-based heterogeneous composite whose uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) are dependent on cement dosage, solid content, sample type, etc. In this paper, uniaxial compressive test and ultrasonic pulse velocity test of three types of backfill samples (7.07 cm×7.07 cm×7.07 cm cube, Φ5 cm×10 cm cylinder and Φ7 cm×14 cm cylinder) were performed, and the effects of cement dosage, solid content and sample type on the backfill strength and ultrasonic pulse velocity were investigated by grey correlative degree analysis. The results show that cement dosage is the key to the backfill strength with a correlative degree of 0.837, while the ultrasonic pulse velocity is mostly influenced by solid content with a correlation degree of 0.712. An exponential prediction relation between UCS and UPV and a BP neural network prediction model were built, and they were validated by F-test and t-test of statistical analysis, respectively. The methods proposed can be new approaches for predicting the backfill strength.
Abstract: In order to solve the high pressure and serious worn problems at some sections in a low stowing gradient backfilling pipeline, this article introduces a new solution of spiral pipes to regulate the resistance and pressure. The regulator of increasing resistance and its implementation plan are analyzed by using the CFD technique. An amended formula for calculating the stowing gradient is presented by adding spiral increasing resistance based on the simulation. It is shown that, when the transportation speed is 2 m·s-1, the unit-height resistance of the spiral pipe can be 10.1 to 16.8 times that of the straight pipeline. This apparatus can fully guarantee the continuous conveying of slurries, and it can also increase the resistance and reduce the pressure effectively. The amended formula can figure out the effective stowing gradient of the backfilling pipeline with spiral apparatus more accurately.
Abstract: Simulation experiment was performed on the performance of concrete exposed to sulfate attack and dry-wet cycles. Changes in ultrasonic velocity and acoustic emission activities for concrete at different erosion periods were tested by uniaxial compression test. The damage mechanism was analyzed by environmental scanning electron microscopy (ESEM), energy-dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). The results show that at the beginning of loading for concrete after 60 d and 80 d erosion, the specimen exhibits a significant compaction phase. The longer the concrete is exposed to sulfate attack and dry-wet cycles, the earlier the sudden drop in ultrasonic velocity occurs. For concrete after 40 d erosion, the active zone of acoustic emission is narrow during the loading process. The problems of stress concentration and a sudden release of energy tend to occur at the weak position caused by erosion in concrete, and a sharp increase in acoustic emission events appears in advance under sulfate attack. By means of a mathematical model, the damage model of concrete was established based on the cumulative ring-down count of acoustic emission as a variable, which reveals the relations of sulfate attack, load and damage for concrete in complex underground environments. During erosion time, the expansions caused by ettringite and gypsum and the swelling of sodium sulfate crystallization result in the evolution of micro-destruction, leading to the different macroscopic properties of corroded concrete.
Abstract: The technical feasibility of desulfurization, denitration and dioxin removal from sintering flue gas processed by blast furnace was discussed in theory. The reduction thermodynamics of sulfur dioxide and nitrogen oxides as well as the conditions for dioxin decomposition in a blast furnace were analyzed. The effects of blast with sintering flue gas instead of air on the theoretical flame temperature (TFT), blast volume, gas in hearth, top gas and sulfur content of hot metal were investigated. The results show that sulfur dioxide and nitrogen oxides can be reduced in the BF interior, and the lowest equilibrium volume fractions of sulfur dioxide, nitric oxide and nitrogen dioxide are 1.84×10-13%, 3.08×10-11% and 3.72×10-21%, respectively. Favorable thermodynamic conditions for dioxin decomposition are found in the blast furnace. Sulfur dioxide and carbon monoxide in sintering flue gas have little effect on the TFT, while nitrogen oxides can slightly increase the TFT. The TFT decreases by about 40.5% with a 1% increase in carbon dioxide volume fraction of sintering flue gas, but the thermal state of a hearth can be improved to the normal level by reducing the humidity and increasing the oxygen enrichment of blast. The blast volume, gas in hearth and top gas decrease with increasing carbon dioxide content of sintering flue gas. As the carbon dioxide content of sintering flue gas rises, the carbon monoxide and hydrogen contents of gas in hearth and the carbon monoxide, hydrogen, carbon dioxide and water contents of top gas increase, but the nitrogen contents of gas in hearth and top gas decrease. The sulfur quality content of hot metal is proportional to the sulfur dioxide content of flue gas and it is raised to 0.025% when the sulfur dioxide content increases to 2000 mg·m-3. The BF production can proceed smoothly with sintering flue gas blast instead of air through comprehensive operating measures, achieving the purpose of desulfurization, denitration and dioxin removal.
Abstract: The gas-liquid inteffacial area has significant influence on kinetic processes, such as heat transfer, mass transfer and physiochemical reactions in two-phase flow. A new method for getting this parameter is introduced to compute the inteffacial area with the numerical simulation results of two-phase flow. Referring to the idea of a piecewise linear interface calculation (PLIC) method, it uses a plane in each cell to approximate the real curved interface between two phases, these planes are then categorized into five types according to the volume fractions of the target fluid and their gradient vectors in each cell, and the inteffacial areas are respectively calculated by different equations for different plane types. This method is applied in analyzing the numerical simulation results of a copper converter. It is shown that this method can extract the interfacial area of any spatial region effectively in a two-phase flow system and can be used in analyzing the features of kinetic processes quantitatively in a two-phase dispersion system. Moreover, by using the computed interfacial area, the oxygen utilization ratio is calculated and the "highly efficient reaction zone" in the bath is recognized. The results agree with practical data and experience, indicating the accuracy of the proposed method in some extent.
Abstract: Based on a moving boundary approach, a three-dimensional dynamic model is built for 2400 mm ~400 mm wide-thick slab molds by using ProCAST to realize the coupling simulation of flow field, temperature field and stress field. The results show that the position of the lower recirculation zone moves to the slab center by the effect of the solidified shell, which reflects the real flow condition of molten steel in the continuous casting mold. The liquid on the free surface flows from the narrow surface to the nozzle, the velocity increases first and then decreases, and the maximum velocity is about 0.21 m·s-1, which occurs at 0.7 m from the nozzle. The center of the narrow face shell at the mold exit is the thinnest and increases from the center to both sides gradually, and the minimum thickness is about 10.4 mm. The wide face shell influenced by water flow impact grows more Unifornl than the narrow face, the wide face shell thickness near the corner is 18.9 ram, and the center thickness is 27.6 mm. The stress change trend of the slab shell is almost consistent with temperature, demonstrating that the initial solidified shell stress is mainly thermal stress. The effective stresses on the wide face and narrow face rise along the drop direction of mold height, and the maximum stresses of the slab corner, wide faee center and narrow face center are about 200, 100 and 25 MPa, respectively.
Abstract: The effects of vanadium on the microstructure refinement of automobile beam steel with a yield strength of 700 MPa were investigated by Gleeble-3500 Thermo Simulator, scanning electron microscopy, transmission electron microscopy and electron back-scattered diffraction. The results show that a mixture structure of acicular ferrite and granular bainite can be obtained in a cooling rate range of 2 to 7℃·s-1. It is recognized that the volume fraction of granular bainite increases and the microstructure can be refined by adding vanadium. After the addition of vanadium, the size of M/A islands decreases obviously. Compared to the V-free steel, high angle grain boundaries in the V-bearing steel increases by 18.2%, indicating a potential improvement in toughness. No VC precipitation is observed in the tested steel due to low carbon content, so it can be deduced that V in the solid solution can promote the bainite transformation and refine the microstructure.
Abstract: The effects of two different thermomechanical control processes (TMCP) including medium temperature slow cooling and medium temperature isothermal treatment after roiling on the microstructure and mechanical properties of Si-Mn series bainitic steel were investigated in this paper. The mechanical properties of the steel were studied by a tensile testing machine, the microstructure was characterized by means of scanning electron microscopy and electron backscatter diffraction, and the amount of retained austenite in the steel was determined by X-ray diffraction analysis. The results show that, as the starting slow cooling temperature after rolling rises, the tensile strength, hardness and tensile strain hardening exponent n increase, the elongation rate and the impact toughness decrease, and the yield-strength ratio decreases first and then increases. When the isothermal time after rolling extends, the tensile strength and the yield-strength ratio of the steel first decrease and then increase, but the elongation and the impact toughness have a reverse trend. Compared with the isothermal regime, the continuous slow cooling can get better comprehensive mechanical properties, the product of tensile strength and elongation is higher, and the elongation is 20% higher than that of the former.
Abstract: Zn-11%Al, Zn-11%Al-1.5%Mg, Zn-11%Al-3%Mg and Zn-11%Al-4.5%Mg alloy coatings were obtained by dipping pure iron in the alloy bath at 510℃ for different immersion time. The effects of Mg content on the solidification structure of the Zn-11% Al coating and the growth of the Fe-AI intermetallic layer in the alloy coating were investigated by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. The results show that the solidification microstructure of the Zn-11% Al alloy coating is composed of Al-rich phase and Zn/Al ternary eutectic. With the increase of Mg content in the Zn-11% Al-x% Mg alloy, Zn/Al/MgZn2 ternary eutectic, blocky MgZn2 phase and AL/MgZn2 binary eutectic occur gradually. The intermetallic layers in the Zn-11% Al alloy coatings with different amounts of Mg consist of Fe2Al5Znx phase and FeAl3Znx phase, and the thickness of the inter-metallic layer increases with the prolongation of immersion time. The increase of Mg content in the hot dip bath reduces the growth-rate index and the growth rate of the intermetallic layer. At the beginning of the hot dip process, a compact and stable Fe-Al alloy layer in the Zn-11% Al alloy coating form on the iron surface. After immersing for 120 s, the Fe-Al intermetallic layer is instable and broken because of diffusion path movement. Mg element in the Zn-11% Al-x% Mg alloy can significantly delay the time of liquid zinc into the Fe-Al alloy layer, which makes the Fe-Al alloy layer be more stable and compact.
Abstract: The effects of cooling rate and Si on the microstructure and corrosion property of the Zn-5Al-0.1 RE alloy were studied by scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, neutral salt spray test and polarization curves. The results show that Zn-5Al-0.1RE-xSi alloys are composed of primary η-Zn phase and η-Zn + α-Al eutectic structure, and the former is uniformly distributed on the adjacent η-Zn + α-Al entectic cells. The reduction of cooling rate and the addition of Si make the grain size increase and the boundary area per unit alloy area decrease; at the same time, the corrosion resistance is improved. The corrosion resistance of the Zn-5Al-0.1 RE-xSi alloys is dependent on their solidification structure and the relative amount of corrosion products including Zn5(OH)8Cl2·H20 and ZnO.
Abstract: Spherical mesoporous NiO powders were synthesized by a hydrothermal-thermal decomposition method, and their morphology and structure were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption/desorption analysis. The electrocatalytic performance of NiO powders were systematically studied by cyclic vohammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). It is found that the prepared mesoporous NiO powders are in spherical morphology with a specific surface area of 35 m2·g-1 and an average pore size of 15.88 nm. They show good electrocatalytic activity for ethanol oxidation; the oxidation current increases with increasing ethanol concentration and scan rate. The current decay at 0.60 V for 1000 s is as low as 0.075%, indicating good stability. CV, CA and EIS measurements show that ethanol oxidation reaction on the spherical mesoporous NiO is a diffusion-controlled process.
Abstract: A The Ni3Al-alloy and its composites with different Cr3C2 contents were fabricated by a hot isostatic pressing (HIP) technique. The influences of Cr3C2 content on the microstructure, hardness and wear properties of the Cr3C2/Ni3 Al composites were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and wear tribometry. The results show that inter-diffusion occurs between the original Cr3C2 and the Ni3AI particles during the HIP process and the Cr3C2 particles partially transform into M7C3 (M=Cr, Fe, Ni) structures. Under specific friction and wear conditions, the wear resistance of the Cr3C2/Ni3Al composites is significantly improved due to the addition of Cr3C2 particles by about 4-10 times, compared to the Ni3Al alloy. In addition, the cutting and scraping effects of counter-part disks by the Cr3C2/Ni3Al composites decreases with increasing Cr3C2 addition, resulting in a reduction in wear rate of counter-part disks.
Abstract: Static compression experiments were conducted on hollow aluminum honeycomb (hexagon aperture), polyurethane, and aluminum honeycomb filled with polyurethane. The mechanical behavior and energy absorption characteristics of the composite were analyzed. Experimental results show that the stress-strain curve of the composite exhibits three stages:elasticity, yield and compaction. The initial stiffness and yield stress greatly increase co,npared to the hollow aluminum honeycomb. Because of the addition of the aluminum honeycomb, the deformation recovery of the polyurethane decreases by 25%. The maximum energy absorption efficiency of the composite is 1.47 times that of the pure polyurethane, and the composite materials show a better energy absorption efficiency than the pure polyurethane under a larger stress. The maximum energy absorption efficiency of the 1 mm aperture aluminum honeycomb with polyurethane filler is 1.37 times that of the 2 mm aperture aluminum honeycomb with polyurethane filler. The larger the loading rate, the greater the peak value of the energy absorption efficiency and the stress at the time of reaching the maximum energy absorption efficiency are.
Abstract: A modified Johnson-Cook model was proposed based on the true stress-strain data of 316LN stainless steel and it was successfully used to describe the deformation characteristic of the steel at room temperature and low strain rate. By making use of the finite element software ANSYS/LS-DYNA, a numerical simulation of cold roll-forming was performed for AP1000 primary pipes. The influence laws of forming parameters on wall-thickness reduction, such as wall-thickness, relative bending radius and friction, were investigated. An empirical formula of wall-thickness reduction for AP1000 primary pipes was proposed by the numerical simulation method. Furthermore, a full-scale cold-bending experiment of AP1000 primary coolant pipes was carried out for verification, and it indicates that the simulated result is accurate and reliable.
Abstract: Wall thinning occurs at transition shoulders in cross wedge rolling (CWR) hollow parts without a mandrel, which will reduce the mechanical strength of the parts, so improving the wall thickness of the shoulder must be resolved. Based on finite element simulations, the cause of wall thinning during the forming process is revealed. A forming method of the anti-wedge upset roiling is proposed to improve the wall thickness of the shoulder, main factors that affect the increase of wall thickness are analyzed, the method of increasing wall thickness and the optimum conditions are obtained, so that a significant increase in wall thickness of the shoulder is achieved for cross wedge rolling hollow parts. The finite element model is validated bv a rolling experiment.
Abstract: Flow past louvers is common in engineering applications. Self-sustained oscillations caused by the flow configuration lead to periodical pressure fluctuations. Because of that, periodic loads will be applied on circumambient structures continuously and may give rise to fatigue problems. Using a numerical simulation method, self-sustained oscillations caused by flow past a louver are studied in this paper. The numerical results show that when the Mach number is small, the self-sustained oscillations belong to a pure fluid dynamic problem. This phenomenon is induced by generation and propagation of large-scale vortices which are generated from fluctuations of the shear layer. In addition, pressure oscillations generated by this phenomenon contain two significant features:sustainability and periodicity. The frequency of the self-sustained oscillations is spatially uniform. Along the mainstream direction, the amplitude of the self-sustained oscillations sharply increases first and then stabilizes. At the impingement edge, it slightly decreases. With an increasing size of the cavity inside the louver, the variation of the frequency basically remains stable. On the other hand, the amplitude increases gradually and remains stable when the cavity size reaches a critical value.
Abstract: In order to improve the thermal efficiency of radiant tubes, a flat double-P type radiant tube was designed, and five major axis-to-minor axis ratios of 1.0, 1.1, 1.2, 1.3 and 1.4 on the cross section of the center pipe were taken for numerical simulation to investigate the influence characteristics of the degree of flattening on the performance of the radiant tube by using the commercial software FLUENT. It is found that in the case of keeping the heat transfer surface area of the radiant tube invariable, when the degree of flattening increases, the radiant angle factor for the radiant tube and strip steel gradually grows, the radiant heat flow improves, and then thermal efficiency of the radiant tube rises. However, with an increase in the degree of flattening, the surface temperature difference of the radiant tube gradually increases, and the surface temperature uniformity significantly deteriorates after the degree of flattening reaches 1.3. In consideration of the thermal efficiency and surface temperature uniformity of the radiant tube, the better degree of flattening is 1.2. At this degree of flattening the radiation heat efficiency of the radiant tube increases by about 1% compared with that at the degree of flattening of 1.0, while the surface temperature uniformity is almost the same.
Abstract: To effectively solve the scheduling problems of dual-blade cluster tools with parallel processing chambers and reentrancy constraints in semiconductor manufacturing, this article introduces a scheduling method centering on optimal searching. Firstly, according to the optimization search rule (FIFO), a mathematical programming model of 4-chamber dual-blade cluster tools with parallel processing chambers and reentrancy constraints was built to minimize the makespan of the system. Combined with the concept of virtual buffer module, an optimum searching algorithm was proposed based on the robot swap strategy. Finally, simulation experiments were conducted for the proposed algorithm, and the results indicate that the algorithm is feasible and effective.
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
