Abstract: Surrounding rock structures of steep seams and gently inclined seams are different. Basic roof and immediate roof of horizontal section top coal caving were beside the working face in steep seams. A judgment criterion of roof destruction was attained by analyzing tension to basic roof. According to the judgment criterion, it was verified that only one part of overlying strata was loaded to exposed rock board. There is unloaded arch structure in overlying strata. The unloaded arch structure bears most weigh of overlying strata and effects later strata behavior of the working face. It is pointed out that the unloaded arch structure is a dynamic expansion structure. It will move towards roof as original balance of arch was broken and keeps a new balance. The scope of arch is a process constantly to expand from balance to instability.
Abstract: Underground excavation is an unloading process, which not only results in the change of stress distribution in surrounding rocks, but also gives rise to the change in rock properties. In order to analyze the stability of slope and optimize the design, studies on the change in mechanical properties of rocks, due to unloading process caused by excavation in an open-pit mine, must be carried out. In uniaxial loading and unloading process, the damage process in rocks was tested by ultrasonic wave and acoustic emission, in which the damage development was dynamically measured by acoustic emission and the damage degree was quantitatively estimated based on ultrasonic wave. The result shows that new damage can be induced in both loading and unloading processes. The damage development and its evolution process can be dynamically measured by monitoring of acoustic emission, and the level of damage evolution can be quantitatively estimated by the signal characteristics of ultrasonic wave.
Abstract: With tabia which is composed of saline soil, lime and crushed stone as an example of backfill engineering, a series of experiments of physical and mechanical properties were carried out to investigate the compressive strength and contributing factors of tabia. The settlement of the modified saline soil as foundation material was monitored. The settlement monitoring results show that this tabia replacement method is practical for ground treatment.
Abstract: The bearing behavior and reinforcement mechanism of a composite bolt pile was studied through numerical calculation with the FLAC soft. The composite bolt pile was successfully used in several ground-reinforcing engineering. The results of numerical simulation and engineering monitoring show that the bearing behavior of the composite bolt pile is improved in comparison with a single bolt pile, the effective factor and bearing capacity of the pile are obviously enhanced.
Abstract: An Al-Ti-B master alloy was prepared by the reaction of complex halide salts with molten aluminum at high temperature and the thermodynamics principle was analyzed. The effect of extrusion process on microstructure was studied by comparing the microstructure after squeezing with the as-cast microstructure. It is found that TiAl3 blocks become smaller and smoother after extrusion, and recrystallization happens when squeezing, which results in homogeneous distribution of TiB2 particles. Besides, the precipitation of TiAl3 and TiB2 in aluminum melt was investigated by stewing experiment and the factors affecting deposition were described. The methods to slow or impede precipitation of second-phase particles were put forward, and the optimized extrusion process and the addition of proper rare earth were emphasized.
Abstract: Suitable feedstock was obtained after analyzing the rheological properties of silicon carbide ceramics. SiCp package box performs used in pressure infiltration experiment were manufactured through powder injection molding and debinding-pre-sintering process. Experimental results showed that the feedstork with 65% SiCp load and 70% PW (paraffin wax) + 29% HPDE (high-density polyethylene) + 1% SA (stearic acid) had the best injection properties in the wide ranges of temperature and shear rate. The injection part with no defects could be manufactured at suitable injection parameters. The debinder was successfully removed from the injection part by solvent and thermal debinding process. SiCp package box preforms with good appearance, enough strength and proper porosity were obtained by pre-sintering process at 1 150℃, which was up to the request of following pressure infiltration experiment to fabricate SiCp/Al composites package boxes.
Abstract: 93W-5.6Ni-1.4Fe cemented carbides were sintered by spark plasma sintering method, in which the sintering temperature ranged from 1100℃ to 1180℃ and the holding time was 5 min. The properties such as density, hardness and bending strength of the samples sintered at different temperatures were tested, and field spray scanning electron microscopy was used to investigate their appearance and rupture behavior. The results showed that 93W-5.6Ni-1.4Fe cemented carbides with high density were sintered by SPS at low temperature. Besides grain size could be controlled, the hardness and the bending strength could also be improved.
Abstract: The effects of oxygen on the magnetic properties of Sm (Co, Fe, Cu, Zr)z permanent magnets were studied. SEM, EDS and TEM approaches were used to analyze the microstructure of the permanent magnets. The factors that affect the magnetic properties were discussed. The results indicate that the magnetic properties remain excellent and are not affected when the oxygen content is less than 0.32% in mass fraction. The magnetic properties begin to decrease when the oxygen content is between 0.32% and 0.4%, evidently deteriorate when the oxygen content is above 0.4%, and almost vanish when the oxygen content is more than 0.7%. The particle size of the magnets decreases while more Sm2O3 begins to separate from the magnets gradually. The main factors that affect the magnetic properties are the increase of non-magnetism phase and the decrease of the useful Sm content of the magnets.
Abstract: A new designed piezoelectricity sensor system was equipped to detect the impact pressure of collapsing cavitation bubbles induced by a spark-generated system for understanding the dynamic of collapsing bubbles on metal surface. The bubble collapsing process was described and analyzed, and the second bubble collapse theory was verified. The dynamic energy of the two stages of bubble collapse was given. More important, the impact pressure and the impulse were determined and calculated at different distances between the collapsing bubble and the metal surface, and the two characteristics were compared.
Abstract: Using Pt-Ru/C and Pt/C as anode and cathode catalysts, the membrane electrode assembly was prepared and a single direct methanol fuel cell system was installed. The electrochemical performance of a direct methanol fuel cell (DMFC) at different technological parameters such as methanol flow, methanol concentration, methanol temperature and humidifying air temperature was investigated by means of steady-state galvanostatic and potentiostatic polarization. The experimental result shows that the output current density and power density were 68 mA·cm-2 and 14.8 mW·cm-2 respectively with ambient air as cathode oxidant when the working temperature was 25℃ and the output voltage was 0.22 V. The four technological parameters significantly affected the performance of a direct methanol fuel cell. In the experiment, the optimum technological parameters were the methanol flow of 2 mL·min-1, the methanol concentration of 2 mol·L-1, the methanol temperature of 30℃ and the humidifying air temperature of 40~60℃.
Abstract: With plasma as heat source, Fe-based alloy powder was cladded on the surface of 16Mn steel and the microstructure and phases of the clad coating were analyzed. The thermal cycle characteristics of plasma cladding and the cladding process were discussed. The heat-affected zone was studied and divided into three zones, i.e., overheated zone, perfect phase transformation zone and imperfect phase transformation zone. In the overheated zone, the microstructure was coarse, Widmanstaten structure generated and the hardness fell down. In the perfect phase transformation zone, the microstructure was refined, and hardness was higher. In the imperfect phase transformation zone, part phase transformation generated, and the microstructure was nonhomogeneous. The Widmanstaten structure in the overheated zone made the heat-affected zone brittle.
Abstract: A kind of composite material of 316L stainless steel and Y2O3 partly stabilized zirconia (Y-PSZ) was prepared by powder metallurgic process. The effects of the content and size of 316L grains on the microstructure, relative density and hardness of the composite were investigated. The results showed that the relative density, shrinkage ratio and HRC value of the sintered samples decreased with the increase of 316L content. When the content of 316L kept constant, the relative density, shrinkage ratio and HRC value of the sintered samples decreased with the increase of 316L particle size. The relative density value was in the range from 92.5% to 95.5% in the present research conditions.
Abstract: The edge cracking causes of hot rolled strips produced by CSP were investigated by optical microscope (OM), scanning electron microscope (SEM), transmittion electron microscope (TEM) and energy-dispersive X-ray analysis (EDX). The results indicated that deep oscillations of thin slabs were the origin of the edge cracks of hot rolled strips and AIN precipitates around the prior austenite grain boundaries due to intensive cooling rate rendered the slabs more susceptible to cracks. After seven rolling stands, the transverse cracks of the slabs would propagate to serrated edge cracks, even drop-out type cracks of hot rolled strips.
Abstract: Nonlinear thermal coupling FEM was used to investigate the temperature field and thermal deformation of roll sleeve during twin-roll strip casting. The distribution disciplines of casting roll temperature and hot deformation were figured out in the steady casting stage. The influence of casting velocity on the distribution disciplines of casting roll temperature and hot deformation was analyzed. It is concluded that during the steady casting stage, the casting roll temperature only fluctuated on the surface of the casting roll; however at the core, the temperature was fairly stable. The lower the casting velocity, the larger fluctuation amplitude was.
Abstract: With special supporting structure for heavy loading, a bottom main drive spindle's breakage appears in strip production of the R2 roughing stand in a 2250 mm hot strip mill. Based on the Marc software package, a 3-dimensional finite element model was constructed to analyze the combined bend and torsion stress state of a bottom main drive spindle in the R2 roughing mill. Under different loading situations of torsion, bending or both them, the results of finite element analysis show that the stress in the special supporting area is greater 60% than that in other normal areas of the spindle in different computing cases. It is also shown that torque is the main reason leading to cracking and breakage of the spindle. The maximum stress in the main drive spindle supporting area after replacing original hollow structure with improved solid structure is reduced by 21%. The reinforced main drive spindle was successfully applied in production of the roughing mill.
Abstract: A vibration suppressing approach for the rolling mill drive system was put forward, which adopt the complex compensative control based on H∞ filter and load observer, on the analysis of a two-mass electrometrical model with two-loop drive and engineering practice. Besides the conventional load observer loop, a pseudo roller speed loop was added by means of the roll speed observer value from H∞ filter constructed by soling the EVP problem of LMI. Compared with the conventional state observer and load observer method, the proposed method loosed the suppose condition of the conventional observer method, and combine the compensations from the load observer and state observer to accomplish integrated vibration attenuation of the motor and roller. Simulation proved that the method achieved better vibration attenuation effect on both the motor and roller than the traditional load observer method.
Abstract: In order to improve the shape control performances of hot strip mills and the shape quality of strips and to reduce production consume, special contour technologies of work rolls and backup rolls were developed for this type of hot strip mills whose work rolls can shift axially, on the basis of large amount of finite element simulations. Relevant shape control models were also set up, including the shape setup control model in process control system (LEVEL 2), the bending force feedforward control model, the crown feedback control model and the flatness feedback control model in basic automation system (LEVEL 1). After several complicated processes such as setup of off-line models, on-line programming, and debugging were finished, roll contour technologies and shape control models were stably applied in an industrial wide strip hot rolling mill. The production data showed the control precisions of profile and flatness, with the crown deviation in the range of ±18μm and the flatness deviation less than ±25 IU, were over 93% and 94%, respectively. And at the meantime, schedule free rolling was realized.
Abstract: An optimization method based on blind number was presented with blind number expressing the uncertain variables in optimization and in combination with the traditional optimization algorithm which based on the real variables. In the microscopic point of view, the relation between design variables and optimization parameters was analyzed and described, and the blind number solution was provided. The blind number solution not only provided the values for design variables, but also provided the evaluation of reliability of the optimization object in optimal condition when the design variables had different values.
Abstract: Based on the multidisciplinary design optimization, a multidisciplinary variable coupling design optimization method for non-hierarchic systems was presented, and its basic ideas and working principle were given. To handle the coupling between subsystems, a coupling function was established by the ideal point during system-level coordination, which was used to coordinate independent optimization of the subsystem and finally obtain the global optimal solution. The method was proved by being used in the design of a comb-finger microaccelerometer.
Abstract: There exists noise signal in the kinetic experiment of desulfurization of flue gas with rare earth oxides by means of isotherm thermogravimetry because of experimental conditions. The contributing factors of the denoising of thermogravimetric signal were discussed by the Daubechies (N=3) function of wavelet transform and Matlab software. The results showed that different rules of threshold and methods of threshold have little effect on denoising, but the number of decomposition layers play an important role in denoising. The optimal number of decomposition layers could be obtained when the rate of signal to noise changed slow. The signal represented the kinetics process of the isotherm thermogravimetric experiment truly after denising.
Abstract: Taking parameter variation into account, a new model of the induced electromotive force relation of a permanent magnet synchronous motor (PMSM) was presented. Two kinds of induced electromotive force observers with high precision, differential and non-differential, were established. The stability and astringency of the induced electromotive force observers was proved. The effect of parameter variation on their position estimation was analyzed. For a sensorless vector control system, the interior permanent magnet synchronous motor for instance was systematically simulated. The results show that the induced electromotive force observers have excellent performance.
Abstract: A kind of linear discrete-time system with multirate control setting was studied and a controller design method was presented for the system. By using discrete-time lifting technique the multirate discrete-time system was reduced to a single-rate system. And then a discrete integrator was introduced by applying state vectors augmentation. Based on the standard linear quadratic optimal prev/ew control theory, the desired preview controller was obtained.
Abstract: A sealed inverse-auction method of resource allocation for computational grids was proposed considering the dynamic, heterogeneous and autonomous characteristics of computing resources in the computational grid environment and the advantages of economics mechanism applied to solve the problem of resource management. A grid service market framework for resource allocation in the computational grid environment was described. A sealed inverse-auction mechanism was presented, where centered on users, and driven by user's needs. The aim was to maximize the total system utility while the QoS requirement of users were fulfilled. Bayes equilibrium point and strategy, efficiency and utility in the Bayes equilibrium state were discussed. A utility function-based resource allocation arithmetic was presented.
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
