Abstract: This article aims at the influence of fault structure on permeability-improved effect and coal-bed deep-hole cumulative blasting safety. The dependence of crack generation and growth upon fault was analyzed on the base of theoretical analysis, numerical simulation and field test. The effect of fault on blasting safety was discussed from two aspects of gas occurrence and blasting energy propagation. Numerical simulation results demonstrate that fault affects blasting crack growth and stress wave propagation. Field test shows that permeability-improved effect in the fault-affected zone is 1.6 times better than that in no fault-affected zone, and that the fault zone, which easily causes punching phenomena, has important influence on blasting safety.
Abstract: A coupled heat transfer and reaction kinetics model was established to study the lithium production efficiency and reduction rate of lithium production retorts. Numerical simulation of the pellet reduction process by this model was performed to obtain the time distributions of pellet temperature and reduction rate, and the effect of effective heat transfer coefficient outside the retorts on the pellet reduction process was analyzed. It is found that the low thermal conductivity of pellets and the chemical reaction equivalent heat sink are the main factors affecting the pellet reduction process. In the beginning of the reaction, heat transfer is the main controlling factor, but in the later, reaction kinetics is the controlling factor. The effective heat transfer coefficient outside the retorts has less influence on the pellet reduction process. Enhancing the heat transfer coefficient inside the retorts is an effective way to improve the production efficiency.
Abstract: AISI M3:2 high speed steels with or without niobium addition were prepared via spray forming, then subjected to forging processes. The effects of Nb on the microstructure and properties of the high speed steels were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It is found that Nb addition can refine the microstructure of the as-deposited steels and decrease the size of M2C eutectic carbides. The amount of MC carbides in the as-deposited steels increases with increasing Nb content. The tempering resistance and second hardening ability of the high speed steel are improved by Nb addition. With a 1% Nb addition, lots of bulk Nb-rich primary MC carbides can form, which becomes the main cause of the reduction in bending strength and impact toughness of the high speed steel. However, the best mechanical properties can be achieved in the presence of 0.5% Nb.
Abstract: A C-Si-Mn-Cr-B hot stamping steel was designed to improve its comprehensive properties. The continuous cooling transformation (CCT) curves and phase transformation rules of 30SiMnCrB5 hot stamping steel were measured and studied by thermal dilatometry. The microstructure morphology and mechanical properties of 30SiMnCrB5 steel sheet after rolling, annealing and hot stamping simulated were analyzed by scanning electron microscopy, transmission electron microscopy and tensile testing. The orientation relationship between martensite variants and parent phases in the hot-stamped steel sheet was determined by pole figure contouring. It is found that the critical cooling rate of 30SiMnCrB5 hot stamping steel is 5℃·s-1 with good hardenability which inhibits the formation of pearlite and bainite effectively. The hardness of full martensite is more than 600HV. The microstructure of the hot-stamped steel sheet is composed of lath martensite and retained austenite, which accounts for 6% to 8% and distributes between martensite laths by film. The strength and ductility of the hot-stamped steel sheet are matched well with a tensile strength of about 1800MPa and a total elongation up to 10%. The orientation relationship between martensite variants and parent phases in the hot-stamped steel sheet is closer to the N-W orientation relationship, which the 12 variants do not appear wholly in prior austenite.
Abstract: Virgin as-cast Cr35Ni45Nb tubes were carburized firstly by low-pressure vacuum carburizing at 1080℃. Then the carburization behaviors and corresponding phase evolution mechanisms in the inner wall were systematically investigated through X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. It is found that the major controlling factor during the carburizing process varies from diffusion control to diffusion and surface reaction integrated control. In general, the diffusion process is accompanied by heterogeneous or multiphase reactions. Compared with the original microstructure and morphology, several newly formed zones appear including bulk carbide scale on the external surface, subsurface depleted zone, lamellar carbide zone, regular geometric carbide zone, diffusion region and weakly affected region. All of these regions display a layering distribution including M7C3, M7C3-M23C6 mixed zone and M23C6. In addition, the formation of surface carbide scale promotes Cr depletion in the subsurface, leading to subsequent depletion of chromium carbides; the cause of lamellar carbides is the low permeability of carbon in the high-nickel-chromium alloy and the blocking effect of precipitates to diffusion.
Abstract: Striated surface textures with different incline angles were manufactured on stainless steel surfaces by electrical machining． The tribological properties of two different texture samples were tested with a tribometer ( UMT-3) ． The friction coefficient of the friction pairs was investigated under dry friction and oil lubrication conditions. The influence of the incline angle of striated surface tex-tures on the friction behavior was analyzed. It is found that the friction coefficient experiences a process of first decrease and then in-crease when the ball sliding on the textured surfaces, that is, the existence of striated surface textures leads to friction coefficient fluctu-ation. Compared with the vertical striated surface texture, the incline striated surface texture results in obvious friction coefficient fluc-tuation, and the fluctuation amplitude relates to the textural incline direction. When the direction of friction is the same as the textural incline direction, the fluctuation amplitude is greater than that in the opposite direction.
Abstract: A finite element model of Q345B ultra-heavy plate rolling was established and the effect of temperature gradient on the strain in the plate core was investigated during the rolling process. The grain size after austenite recrystallization was calculated and compared with tradition processes. The result of simulation was proved by large specimen plane stain experiment and indicated that the process with temperature gradient is favor of strain increasing in the plate core, and the maximum of increment is 61.35%. The calculation and experiment proclaim that the grain size in the plate core is refined by temperature gradient rolling, moreover, increasing the mechanical properties of the ultra-heavy plate.
Abstract: The fretting wear behavior of Inconel600 alloy for steam generator heat exchange tubes at different displacement amplitudes was investigated with a SRV IV fretting tester. The effects of displacement amplitude on the friction coefficient and wear volume were analyzed. The worn surface and subsurface morphology were observed by optical microscopy and scanning electron microscopy, and the tribological transformed structure was observed by transmission electron microscopy. It was found that the friction coefficient and wear volume increased with the displacement amplitude, and the fretting wear mode gradually transformed from mainly adhesion of the partial slip regime to absolutely slide of the gross slip regime. The wear mechanism correspondingly gradually changed from adhesive wear to a combination of oxidation and delamination wear. Microcracks were observed at the junction of the adhesion zone and the slide zone and in the whole slide zone of the wear scar. The oxygen distribution density in the adhesion area was almost the similar as the matrix located outside the wear scar, and oxidation mainly occurred in the sliding zone. Severe plastic deformation appeared just under the wear scar, resulting in its nanolization. The grain size in the tribological transformed structure layer was about 100nm, much smaller than 15 to 30 μm of the original grain size.
Abstract: Surface tension is one of the major parameters for mineral wool production, and it may influence burdening and processing parameter selection. The surface tension of melts for mineral wool production using blast furnace slag as a major material was systematically investigated by experiment measurements and model forecasting. Firstly, a series of surface tension values of SiO2 (40%-60%)-Al2O3 (5%-20%)-CaO(20%-30%)-MgO(5%) quaternary systems were measured, and they showed in the range of 350 to 500 m·m-1. Then in combination with data from reports in literature, an artificial neural network (ANN) model was constructed to calculate the surface tension of melts in an extension system of SiO2 (35%-60%)-Al2O3 (5%-20%)-CaO(20%-45%)-MgO(0-10%). The average error of the developed model is 9.32%, proving a higher accuracy for predicting the surface tension of those melts in the extension system.
Abstract: It is emergent to study and develop new ceramic (glass) matrix composites with high thermal conductivity. Improving the bonding condition of the interface between the matrix and reinforcement is an important way to increase the thermal conductivity of these composites. Based on copper plating and controlled oxidation of diamond particles and Cr-coated diamond particles, diamond reinforced glass matrix composites were successfully synthesized by spark plasma sintering (SPS). Their micro-morphology, interface bonding condition and thermal conductivity were investigated. It is shown that diamond particles are distributed in the glass matrix uniformly, while the Cu/diamond interface and Cr/Cu interface are the weakest bonding interface in the two types of composites, respectively. The thermal conductivity of these composites increases with increasing diamond content. The thermal conductivity of the diamond/glass composites decreases with increasing Cu coating thickness; because of chemical bonding between Cr and diamond particles and Cr diffusion in Cu coatings, the thermal conductivity of the Cr-coated diamond/glass composites increases with increasing Cu coating thickness. When the diamond particle size is 100 μm, the diamond volume fraction is 70% and the Cu coating thickness is 1.59 μm, the Cr-coated diamond/glass composite has the highest thermal conductivity about 91.0 W·m-1·K-1.
Abstract: The slot-type porous plug used for injecting pulverized coal into the ladle through a bottom position is an extremely important element for desulfurization during hot iron pretreatment, and it makes great effect on the trouble-free operation of this desulfurization technology. With the help of the Eulerian—Eulerian model and the particle dynamic theory, a three-dimensional model is constructed to evaluate the velocity, pressure and concentration fields of gas—solid two-phase flow in the slot of a porous plug. It is found that the concentration nonuniform length in the slot is about 250mm, the acceleration length is always less than 250mm, and the maximum difference in pressure is 2350 Pa on condition that the particle size is 20 μm. The result of industrial application shows that the desulfurization efficiency of coal injection through the bottom position is about 15% higher than that by the top lance.
Abstract: The effects of electromagnetic stirring on the flow field and level fluctuation were researched for 260mm×300mm bloom molds by combining the finite element method with the finite volume method. The simulated magnetic field is consistent with measured data in a real plant. Molten steel swirls in the horizontal section and forms two pairs of recirculation zones with opposite circulation directions in the longitudinal section. When the current and frequency increase, the maximum tangential velocity increases, and the level fluctuation of the free surface aggravates. For 260 mm×300 mm bloom continuous casting of bearing steel, the reasonable current and frequency of mold electromagnetic stirring are 300 A and 3 Hz, respectively.
Abstract: As a crucial device of steel mills, the draught fan plays a key role in converter dedusting and gas recycling, and thus it is significantly essential to predict the remaining useful life (RUL) of the draught fan. In this paper, a Wiener process-based degradation model is constructed based on vibration data analysis for a draught fan in the Handan steel mill. An analytical expression of the probability density function (PDF) of RUL is derived on the concept of the first hitting time (FHT). A parameter updating scheme is deduced on the basis of the maximum likelihood estimation (MLE) algorithm for the RUL online prediction of the draught fan. Comparative studies with existing models show that the proposed method can predict the RUL of the draught fan in real time with a higher accuracy and less uncertainties.
Abstract: Hybrid energy storage systems (HESS) play an important role in electric vehicles. This paper mainly focuses on a hardware-in-the-loop (HIL) test bench for testing the performance of HESS. The scenario of an induction motor and a DC motor was proposed. The induction motor was used as a traction motor while the DC motor worked as the load and moment of inertia of the vehicle. Speed control was implemented on the induction motor while torque control was applied to the DC motor. The speed, torque and power of the traction motor were obtained from a simple drive cycle based on real parameters. The motor speed was given as a reference of the induction motor while the load torque was used as a reference of the DC motor. The speed control system of the induction motor and the torque control of the DC motor were analyzed and designed. Meanwhile, the speed control system of the induction motor was modeled. Adaptive fuzzy neural-network control was proposed to achieve high accuracy due to the low accuracy of PID control. Simulation and experimental results agreed with the proposal. The test bench follows the reference speed and reference torque well.
Abstract: Zirconium powder is widely applied as high-energy fuel for it has not only a faster burning speed but also a stronger burning heat. Flame comes into being from the combustion of zirconium dust cloud with a lot of zirconium particles suspending in the air. A transient flame propagation experimental system was established to study the flame temperature and flame propagation speed characteristics of zirconium dust cloud in a vertical pipeline. The results indicate that the maximum flame temperature and the maximum flame propagation speed of zirconium dust cloud have the same changing trend at thermocouple positions, i. e., both their values increase firstly and then decrease with the increasing concentration of zirconium dust cloud. The maximum flame temperature reaches 1777.81℃and the maximum flame propagation speed is up to 39.7 m·s-1 when the concentration of zirconium dust cloud at 0.625 kg·m-3. But when the concentration exceeds 0.625kg·m-3, both the maximum flame temperature and the maximum flame propagation speed decrease. The main reason is that zirconium particles occur incompletely burning owing to rich fuel combustion in the pipeline.
Abstract: A mathematical model of the optimum route for transporting goods and materials during a disaster period was built by using the graph theory and multi-objective optimization method. For the simple case of a dual-objective optimization, an approximate and fast algorithm was proposed based on the heuristic algorithm and then we extended the promotion to other transportation route optimization problems, which contain 3 and more than 3 optimization goals. The dynamic network routing problem was transferred into a static network routing problem by introducing the time-expanded graph in dynamic network flow analysis, which can provide an appropriate method for selecting the optimum route of transporting emergency goods and materials. The purposes of the algorithm are to call Dijstra algorithm to calculate the model by constructing several decision support functions and to find the optimal solution in the search space constituted by the auxiliary functions, so the algorithm is a fast and approximate algorithm. The algorithm was tested in a random road network and a real road network, and the results are consistent with theoretical analysis in the text. The test results show that the algorithm has a better effect in solving the multi-objective route optimization problem of transporting emergency goods and materials and its solution efficiency is higher.
Abstract: Based on a synchronous machine in an AC—DC—AC variable frequency speed-regulating drive system, a new power supply method of phase-shifting combination is proposed by a detailed study on the impact of power grid harmonics. With regard to the auxiliary motor drive system of a hot-rolling mill, the grid side harmonic rate and waveform distortion rate are quantitatively analyzed when the parameters of the power load, LC filter, pulse-width modulation circuit and transformer change. Simulation results show that the power supply method with the reasonable parameters3 design of the drive system can drastically reduce the grid side harmonic interference that the total harmonic distortion is suppressed within 4.0%. This study provides an effective method for the design of a factory drive system and a reactive power compensation system as well as the fault diagnosis of an electric drive system.
Abstract: To overcome the limitation of mobility models for the closed-form analysis of capacity and delay in mobile ad hoc networks, the paper introduces a new probability theoretical framework in order to extend a memory-less independent and identically distributed mobility model to a more realistic random waypoint mobility model with certain memory, which solves a series of complex probabilistic problems caused by the way of local move in the random waypoint mobility model. The two-hop relay algorithm with packet redundancy is also investigated and then the accurate closed-form expressions of capacity and delay are obtained. Simulation results demonstrate the efficiency of the proposed probability theoretical framework and prove the accuracy of the closed-form theoretical expressions.
Abstract: To develop fast and efficient methods to cluster mass document data is one of the hot issues of current data mining research and applications. In order to ensure the clustering result and simultaneously improve the clustering efficiency, a document clustering algorithm was proposed based on searching a document pair with minimum similarity for each other and its distributed parallel computing models were provided. Firstly a document similarity measure was presented using a vector space model (VSM); then bisecting clustering was raised combining the bisecting K-means and the proposed initial cluster center selection approach to find the optimized cluster centroids by once partitioning; finally a distributed parallel document clustering model was designed for cloud computing based on MapReduce framework. Experiments on Hadoop platform, using real document datasets, showed the obvious efficiency advantages of the novel document clustering algorithm compared to the original bisecting K-means with an equivalent clustering result, and the scalability of parallel clustering with different data sizes and different computation node numbers was also evaluated.
Abstract: The base reaction of CFG pile composite foundation with non-uniform pile arrangement was numerically calculated by applying interaction analysis software that can consider the isoparametric elements of medium plates on a limited compressible foundation, and it was compared with that of uniform natural foundation and CFG pile composite foundation with uniform pile arrangement. The results show that if the piles are placed more densely at the core tube area than the external frame column area, the maximum settlement and the raft3s relative deflection are obviously smaller than those of the uniform pile arrangement. The base reaction distribution of non-uniform pile arrangement is quite different from that of uniform pile arrangement and it correlates well to the modulus of the composite earth layer:the base reaction is the largest and distributes evenly, nearly a linear distribution, within the extent of 1 time the slab thickness surrounding the core tube area; the effective transfer range of load is 2.5 times the slab thickness, and the base reaction gradually decreases within the extent from 1 time to 2.5 times the slab thickness surrounding the core tube area; the base reaction reaches minimum outside 2.5 times the slab thickness and distributes uniformly, almost following a linear distribution. On the whole, the base reaction shows a basin-shaped distribution.
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
