Abstract: In order to solve the mechanical problems during tunnel-supporting design under the mined gob with a thin roof coal seam, orthogonal experiments with 7 factors and 3 levels including 27 numerical simulations were carried out. The influence of the key factors on the tunnel stability was analyzed and corresponding optimized schemes were chosen according to 3 evaluation standards. The grey-fuzzy theory was utilized to make comprehensive evaluation and overall optimizing design. Cost factors such as supporting expense and construction time were considered during the study. The stress transformation, displacement character and failure mechanism of wall rock after support were analyzed, and a feasible construction plan was established. After utilizing the introduced supporting technique formally in Tianzhu Mining Zone of Yaojie Coal-electricity Inc. in China, favorable economical benefit is brought.
Abstract: A new method of deformational analysis was adopted to carry out the three-dimensional stability analysis of a slope so as to accord with the actual destruction pattern as possible. In the method, the residual thrust method and the principle of optimality were used to construct the critical slip field (CSF) of the slope, which not only is convenient to find out the arbitrary shape of critical slip surface, but also can be used in optimum design at a given safety factor by using the counter-analysis method. Corresponding software was compiled to calculate a mining engineering project, the calculation results agreed with the measured data, and some optimum design schemes were proposed for the engineering project.
Abstract: To deal efficiently with imprecise and uncertain data associated with structural parameters and exciting loads, a multilevel control method was presented for vibration control of structures based on phase plane analysis. The phase plane was divided into many local grid regions, and the trajectory point corresponding to any instantaneous motion state of the controlled mass could be mapped to a grid region. The control force was obtained by distinguishing the motion trend of the controlled mass. Effectiveness of the proposed algorithm was demonstrated through a numerical example which considered a three-storey structure controlled with the active tendon system (ATS) installed in the first storey. Numerical results show that the proposed algorithm results in significant decrease in the seismic response of the structure when compared to the uncontrolled case, and the control performance of the algorithm is also superior to that of the linear quadratic regulator (LQR) algorithm.
Abstract: In order to detect the damage of simple-supported reinforced concrete (RC) beams, experiment set-up for RC beams dynamic test was designed. In the test, the beam was subjected to an increasing static load in the middle to introduce cracks, and the last load step corresponded to failure. After each load step and unloading, the beam crack width was investigated and an experimental dynamic monitoring was performed. The multipie degree-of-freedom dynamic equation of the testing beam was wavelet transformed, and the structural dynamic response expression on multi-scale was acquired. It is shown that multi-scale decomposition of signal comprises more structural damage information. By means of DASP signal processing system, binary wavelet transformation is applied to the dynamic signal of reinforced concrete beams on different damage states. Through analyzing the wave-figure of all frequency scales, the damage of reinforced concrete beams is determined.
Abstract: The structure of fly ash was analyzed to extend its scope of application. The compressive strengths of Na2SiO3 and fly ash blocks modified by four methods were compared to display the chemical reaction speed of fly ash. SEM photographs showed that after mechanical grinding and alkali activation most of the stiff shells of fly ash were destroyed, and MAS NMR of 27Al showed that wide peaks became narrow. MAS NMR of 29Si indicated that Q0 disappeared, the quantity of Q2 increased but that of Q4 decreased. It is concluded that after mechanical grinding and alkali activation, the hard shells of fly ash are destroyed, the polymerization degree of silicon-oxygen and aluminum-oxygen is reduced, and the potential activity of fly ash is enhanced.
Abstract: The microstructure of twinning induced plasticity (TWIP) steel after tensile deformation was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) analysis. The results show that there are 60% annealing twins in TWIP steel before deformation and 32% deformed twins after deformation. The grains with annealing twins deform firstly during tensile deformation. This deformation mechanism of twinning induced plasticity provides specimens' excellent elongation with no-necking phenomenon. The orientation of the first deformed twin originates from the annealing twin's. The interactions between twin and twin, twin and dislocation, and twin and sliding play an important role during deformation. Therefore the effect of twinning induced plasticity is the main deformation mechanism.
Abstract: Based on the dynamic materials model theories, hyperbolic sine equation and two Liapunov stability criteria, the processing maps of T122 heat resistant steel were constructed using the data obtained from isothermal hot compress tests by means of a Gleeble 3 500 simulator. The hot formability of the T122 steel was studied and its relations with microstructure at various temperatures and strain rates were analyzed using the process maps. The result shows that the efficiency of power dissipation increases with the increase in temperature and the decrease in strain rate, The T122 steel exhibited dynamic recrystallization with a peak power dissipation efficiency of 0.2 occurring at the temperature upwards 1085℃ and the strain rate less than 0.37 s-1 The temperature of 1085~1150℃ and the strain rate more than 0.13 s-1 are recommended to set the industrial forming conditions.
Abstract: The changes in strength, hardness and impact ductility of 5CrNiMo steel added different contents of RE La element were investigated. The 5CrNiMo steels with and without RE addition were compared after treated by the same heat treatment process. The result shows that the strength, hardness and impact ductility of 5CrNiMo steel are obviously improved when added a proper content of RE La element; the 5CrNiMo steel with RE La element of 0.033% in mass fraction has the best mechanical properties.
Abstract: The softening behavior of austenite in X70 pipeline steel was investigated on a Gleeble 1500 thermo-mechanical simulator at different deformation parameters by double-pass hot compression testing. The influence of the parameters such as deformation temperature, interval time between passes, strain rate, degree of reduction, and initial austenite grain size on the mechanism of static recrystallization was analyzed. The softening percentage of static recrystallization under different conditions was defined by the 0.2% stress offset method. On the base of experimental data, the value of austenitic static recrystallization activation energy of X70 pipeline steel is 435.3 kJ·mol-1, and a static recrystallization kinetics model to predict the evolution of softening was developed.
Abstract: The corrosion behaviors of carbon steel exposed to CO2-containing water under high temperature and high pressure for different intervals of time were measured by using an autoclave. The morphology and microstructure of the CO2 corrosion scale were investigated by SEM, EDS and XRD, and its formation mechanism was discussed. The results indicate that the corrosion scale is mainly composed of Fe3C and a little FeCO3 in the beginning period (8 h), and with the process of corrosion (after 72 h) it changes to FeCO3. The corrosion scale consists of inner and outer scales. HCO3- penetrates the scale, reaches the scale/substrate interface and reacts with substrate to form the inner scale, while the formation of the outer scale is attributed to the concentration of Fe2+ and CO32- in the solution exceeding the solubility of FeCO3. The grain size of the outer scale is smaller and denser than that of the inner scale. The adhesion intensity between the inner and outer scales is weak but that between the inner scale and substrate is strong.
Abstract: The solidification microstructure of superalloy IN718 and the contents of Nb and Mo in liquid during solidification were investigated at cooling rates of 1, 3 and 6 K·min-1 by SEM and EDS. The liquid density difference and relative Rayleigh number at different temperatures and different cooling rates were calculated. The results show that the contents of Nb and Mo in liquid and the liquid density difference increase with decreasing temperature due to segregation. The slower the cooling is, the heavier the segregation of Nb and Mo is, and the more liquid density difference at the same temperature. The maximum values of relative Rayleigh number exist at 1 330℃ at all the three cooling rates, with the decrease in cooling rate the maximum values of relative Rayleigh number raise dramatically, and freckle tendency increases. Freckles could form in large industrial ingots at a cooling rate less than 1 K·min-1
Abstract: The finite element technique was used to simulate the temperature field and stress held of multilayer diffusion bonding materials TCA/V/Cu/Ni/GCr15 occurring during oil quenching. The effect of martensitic transformation was considered during the simulation. It is shown that stress concentration appears on the adjacent place of interlayer; martensitic transformation in steel layer can alleviate the stress generated in the heat treatment process; the maximal shear stress appears at the edge of Cu layer before the quenching temperature reaching Ms, The reduction in thickness of bearing steel layer can decrease the maximal shear stress in the workpiece, but it cannot eliminate the fundamental source of failure of the workpiece
Abstract: The experimential investigations on out-of-plane compressive characteristics of brazing mild steel honeycomb sandwich structures were conducted by using a MTS 810 material test system. The influences of structural parameters on the compressive properties of honeycomb sandwich structures were analyzed in terms of the measured data. Three deformation stages, i.e., elastic deformation, plastic deformation and densification, are observed on the stress-strain curve. The initial deformation mode depends on the ratio of cell wall thickness to side length (t/a). The yielding mode dominates initial deformation as t/a > 0.042 7, while the buckling mode dominates initial deformation as t/a < 0.042 7. In all structural parameters, the cell wall thickness has a strong influence on the initial compressive strength and peak compressive strength, the cell wall side length in the next place, and both the facing thickness and the height of core have a weak influence.
Abstract: The weak multi-step reduction of stannous acid on hexachloroplatinic acid was utilized to prepare a new type of Pt/C catalyst. The catalyst was characterized by XRD, HRTEM, EDS, DSC and H-adsorption electrochemistry, and its catalytic activity for electro-oxidation of methanol was estimated by cyclic voltammogram and potentialstatic steady-state polarization. The results indicate that Pt/C catalyst prepared by the new method is with high activity for electro-oxidation of methanol which possesses about two-fold mass activity at 0.5 V (SCE) compared with Pt/C prepared by sulfurous route. The stannous method can produce a composite carbon-supported catalyst with Pt metal and Pt oxides co-exiting within nanometer dimension. The oxo composite catalyst could enhance the harmony of the hi-function of Pt during electro-oxidation of methanol.
Abstract: The molten steel corrosion and ultrasonic vibration resistance of a corundum stick, a tungsten alloy stick, a metal Mo stick coated with ZrO2 outside, and a Mo-Al2O3-ZrO2 ceramic metal tube were investigated for ultrasonic treatment of molten steel. The results show that the corundum stick can endure high-temperature molten steel corrosion, but ultrasonic vibration caused it fracture. The tungsten alloy stick could endure huge ultrasonic vibration but end fusion will take place within a short time during the ultrasonic treatment process of molten steel. The metal Mo stick coated with ZrO2 outside had corrosion resistance ability in molten steel during a short time (1-2 min), however, low ability to withstand strong ultrasonic vibration. The ceramic metal tube had the ability to endure not only strong ultrasonic vibration (250 W) but also high-temperature molten steel corrosion, so it could be served as the probe for ultrasonic treatment of molten corrosion.
Abstract: A new method for the preparation of trimanganese tetroxide (Mn3O4) by air direct oxidizing free divalent manganese was made at a certain temperature and pH value varying correspondingly according to the change of manganese ion concentration. The results show that the rate of oxidization of manganese hydroxysulfate is slower than that of manganese hydroxide, and the package of manganese hydroxysulfate is a basic reason for high sulfate content in Mn3O4. In comparison with the method in which Mn3O4 is prepared by air direct oxidizing the hydrolyzates of manganese, the proposed method can efficiently reduce impurity contents of Ca2+, Mg2+ and SO42- in Mn3O4.
Abstract: In order to study dynamic characteristics of an automobile semi-axes cross wedge rolling mill and to improve the whole performance and precision of rolled work pieces, ANSYS dynamic analysis module was used to calculate the natural frequency and vibration styles of the rolling mill, and the dynamic characteristics of automobile semi-axes cross wedge rolling were analyzed. The results indicate that the design of the rolling mill is dependable according to existing parameters.
Abstract: To estimate the rotor position of a permanent magnet synchronous machine by the method of high-frequency signal injection, the basic and high-frequency voltages should be input into the machine simultaneously. The feasibility to realize this idea by a pulse width modulation (PWM) inverter was discussed and simulated. The results show that this method works well with an appropriate ratio of carrier signal to modulation. The inverter's nonlinear behavior was also studied, and its effects only occur in the time domain as the phase currents cross zero. According to this feature, a simple compensation measure was presented and simulation results verified its correctness.
Abstract: In order to research the dynamics characteristics of involute spur gears with asymmetric teeth, a dynamic model based on virtual prototyping was proposed by setting up an equivalent kinetic model for torsional vibration of asymmetric gears. With this model, the time and frequency domains of vibration characteristic were analyzed taking account of the influence of time-variant mesh stiffness and mesh damping in the course of meshing. These results were compared with numerical simulation and experimental results. It is shown that this simulation method consists with the numerical simulation and experimental method.
Abstract: According to the features of coke bed heat transfer in a coke dry quenching (CDQ) chamber, an experimental setup of CDQ chamber heat transfer was established to test the primary parameters such as coke size and cooling gas flow. In order to deal with experimental data effectively, the average heat transfer coefficient was redefined and its dimensionless equation was deduced. The local heat transfer coefficient of coke bed was numerically analyzed based on the inverse heat conduction problem in the single coke. The experimental data show that the change law of average heat transfer coefficient is similar to that of local heat transfer coefficient. Both of them increase with increasing fluid flux and are sensitive to coke size, and the smaller the coke size, the larger the heat transfer coefficients.
Abstract: Robust stabilization for a class of uncertain switched linear systems whose nominal systems have a common Lyapunov function was considered. With the certain restriction of uncertainty, a kind of robust controller of state feedback was constructed by using the completeness condition and common Lyapunov function technique. The closed-loop system still has a common Lyapunov function. The designed controller can guarantee the states of the closed-loop system asymptotically stable at the equilibrium point under an arbitrary switching strategy. Simulation result shows the validity of the designed controller.
Abstract: To expand the application of chaos control and synchronization in the field ot secure commumcation, anti-control of chaos for three-state discontinuous linear feedback systems was achieved by adding a feedback control item under discontinuous state to a kind of n-dimensional unstable linear systems, the basic dynamical behaviors of the chaotic control systems were investigated in detail, and some theorems were given. Numerical simulation and calculating all Lyapunov exponents verify their chaos.
Abstract: In order to solve the resource scheduling problem in service grid environment to guarantee the need of user jobs complete time, an independent matchmaker was introduced into the three-element service grid model. The service grid model was formally illustrated based on the graph theory, and the necessary and sufficient conditions of complete match of user jobs and grid service resources were also proved. A grid services matchmaking system was constructed on the base of sensor feedback. The optimal matchmaking problem of the system was formally illustrated based on the running time weight matrix, and the optimal solution arithmetic was proposed based on the discrete event dynamic system theory. Simulation analysis shows that the arithmetic can improve the QoS (quality of services) performance parameter of the grid services matchmaking system, provide the user jobs completed time guarantee and meet the load balance need of grid service resources.
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
