Abstract: To achieve the effective monitoring of rock failure events in the mine water inrush inoculation process, a moment tensor inversion method based on digital seismology was introduced to process abnormal microseismic events monitored in Hebei Fanshan Phosphate Mine. The vibration displacement field in the mine scale could be expressed as the convolution of moment tensor and Green's function. The moment tensor was linearly inversed through extracting displacement data from the microseismic events and calculating the Green's function (pulse response of transmission medium between the source and sensors). Then, the type of ruptures was distinguished by analyzing the fracture azimuth of microseismic events. As a result, a 3D effect picture of the microseismic monitoring area was built to fit the rock failure surface, predict its development trend, and demarcate the water inrush danger zone preliminarily. Research results show that the moment tensor inversion method can be used to calculate a series of focal mechanism solutions and can reflect the rock failure in the mine water inrush inoculation pocess and development trend effectively.
Abstract: Column leaching seepage processes were detected in a non-contact and non-destructive way by magnetic resonance imaging. Column leaching images were obtained when the flow was stationary and running. Mesoscopic seepage velocity field distribution characteristics and velocity field evolution rules inside pores were studied by analyzing the velocity value distribution, flow velocity distribution uniformity, and relationship between evenness index and spray intensity. The research shows that the velocity distribution has obvious inhomogeneity, and the flow velocity value is not in accordance with the pore size strictly. The flow velocity distribution is similar for different spray intensities. There is a positive correlation between the maximum velocity and spray intensity. A spray intensity threshold can he obtained by analyzing the relationship between velocity field uniformity and spray intensity. The value of 0.7 L·cm-2 h-1 is the intensity threshold of the designated graded distribution. Field applications of dynamic spray intensity can obviously improve the permeability of dumps and the leaching rate of copper.
Abstract: The oxidation kinetics of iron sheet in CO2 -CO mixture was studied by on-line measuring the composition change of the reaction gas using a gas mass spectrometer under different CO2 partial pressures in the temperature range of 1273 to 1473 K. It is found that the oxidation rate increases linearly with CO2 paltial pressure, the rate constant decreases with the increase of COJCO volume ratio, and the apparent activation energy of the oxidation of iron sheet is (137.7±15.8)k J·mol-1. Compared with the results reported, this on-line mass spectrometry analysis can get reliable resuhs, so it can be used to study the gas-solid reaction kinetics.
Abstract: Oxygen in molten steel was removed with liquefied petroleum gas in laboratory. The results show that it is feasible to use liquefied petroleum gas for deoxidation in molten steel to produce high-carbon and high-quality clean steel with VD vacuum smelting assistance. The deoxidation rate is faster with a mixed gas of argon and liquefied petroleum gas than just using a single gas, the oxygen content decreases more significantly and the rate of increase of the carbon content declines. After deoxidation for 8 min, the velocity of deoxidation decreases, and the oxygen content has no significant declination. At the beginning of deoxidation, the carbon content increases slowly; however, while the oxygen content decreases to a certain level the carbon content rapidly increases. Argon does have effect on stirring molten steel, and lead to having a good dynamic condition to facilitate the removal of hydrogen in molten steel.
Abstract: The morphology, size, composition, and number of inclusions in pipeline steel were characterized by scanning electron microscopy and energy dispersive spectroscopy. The characteristics of the inclusions with different Ti/Mg ratios as well as the influence of sulfur content and the number of deoxidation products on the precipitation behavior of MnS were investigated, and the corresponding thermodynamic calculations were carried out. It is found that the core of the inclusions is mainly composed of MgO-Al2O3-Ti2O3, MgO-Ti2O3 or MgO, and then MnS wraps or locally precipitates on them. The inclusions have the average size smaller than 1.3 txm and the number of 300 to 450 mm-2; moreover, their morphology is diverse such as round, polygonal and square. When the Ti/Mg atomic ratio is 0.05 to 0.2, the inclusions are round and small. With the decrease of sulfur content, MnS less tends to precipitate during solidification, its ways of precipitation on the inclusion surface will change from wrapped to local precipitated. A great number of oxides is conducive to the heterogeneous nucleation of more finely MnS on the surface of complex oxides. The Ti-Mg complex deoxidation products are small and dispersed, can become the heterogeneous nucleation core of MnS, and may reduce the harm of MnS and oxides at the same time.
Abstract: A two-dimensional mathematical model of solidification and heat transfer for round blooms was established with ANSYS software, and it was verified by nail-shooting experiment and surface temperature testing. The solidified shell thickness distribution at any fixed location in the casting direction and the position of the solidification end point can be accurately obtained by using this model. Combining the model results with the macrographs of samples, it is found that the shell thickness and the square root of solidification time show a linear relationship in the columnar crystal zone, which fits a solidification square root law. The law is corrected, and the correction term is relevant to the superheat and solidification velocity. The relationship between the shell thickness and the square root of solidification time in the equiaxed crystal zone is not fit for the solidification square root law. It is indirect argument that heat transfer during columnar crystal solidification is unidirectional, but heat transfer during equiaxed crystal solidification is in multiple directions.
Abstract: The cleanness evolution and inclusion distribution of IF slabs in the thickness direction were studied by original morphology analysis, scanning electron microscopy and energy spectroscopy analysis, and total oxygen (T. O) and nitrogen analysis. The average values of mass fraction of total oxygen and N in the slabs in the thickness direction are within 17 × 10-6. The mass fractions of T. O and N in the area within 1/16 thickness from the slab surface are 5% to 10% higher than the average values, in the area between 1/4 thickness from the inner are and 1/4 thickness from the outer arc are 5% to 10% lower than the average values and in other area are close to the average levels. The average size of inclusions is 5.7 txm based on a total of 963 statistical inclusions. Inclusions with the particle size smaller than 5μm account for 60% and with the particle size smaller than 10 txm account for 90%. Al2O3 mainly exits within 5 mm from the slab surface with the size of 2 to 10μm; TiN-Al2O3 and TiN exist in the area from 5 to 80 mm in the thickness direction, and their particle size grows up as the thickness increasing; TiN-TiS and TiS inclusions mainly exist in the area from 80 to 130 mm in the thickness direction with the size of 1 to 5μm. Inclusions from the slab surface to center are mainly Al2O3, Al2O3-TiN, TiN, TiN-TiS, TiS, and MnS in order.
Abstract: After solution treatment at 1300℃ and cold rolling deformation at different reductions, 2205 duplex stainless steel was homogenized at different temperatures for different time intervals. To study the precipitation behavior of σ phase in the steel, the microstructure of specimens was observed by optical microscopy and transmission electron microscopy, and the volume fraction of σ phase in the microstructure was calculated by Image Tool software. The results show that when the steel is homogenized at 950℃, the precipitation time of σ phase is shortened from 30min to 3 rain with the increase of cold rolling reduction from 50% to 85%. As to specimens with a cold rolling reduction of 85%, the volume fraction of σ phase increases from 1.2% to 11.8% when the homogenizing time is prolonged from 3 min to 30 min at 950℃ However, after homogenization for 5 min, the volume fraction of σ phase decreases from 8.9% to 3.6% with the rise of temperature from 875 to 950℃; moreover, when the homogenizing temperature is 975℃, No phase exists in the specimen.
Abstract: The high temperature oxidation characteristics of C-Mn steels containing As or Cu + As were investigated by thermo-gravimetry, scanning electron microscopy, and electron probe micro-analysis. It is shown that the oxidation kinetic curves at 1050℃ obey a linear law in the first 500 s and subsequently change to a parabolic law. The parabolic oxidation rates of the As and Cu-As steels are higher than that of the C-Mn steel. Due to separation of the scale from the matrix, the mass increment of the steels at 1150℃ is smaller than that at 1050℃. Cu and As in the steels could promote solid Fe2SiO4 layer growth. A significant internal oxidation particle layer is observed in the As steel because of As enrichment at the scale/steel interface at 1050℃. The interface is found to be uneven when Cu and As are added to the C-Mn steel, and the number of internal oxides increases with increasing oxidation time and temperature. The oxidation enrichment degree of Cu and As at the scale/steel interface at 1050℃ is higher than that at 1150℃.
Abstract: Slurry wear tests of three designed pipeline steels with the same chemical composition but different microstructures were performed by utilizing a wet sand/rubber wheel abrasion test apparatus. The worn surfaces were further investigated by scanning electron microscopy and 3D white light interference analysis to reveal the wear mechanism and the relation between the microstructure and wear resisting perforumnce. It is found that the mass loss increases with the increase of the micro-hardness difference between two phases in the muhiphase strueture when the predominant wear mechanism is micro-ploughing combined with micro-fatigue. That is due to a misfit of micro deformation between the hard phase and the soft phase. Among the three different muhiphase steels with nearly the same mechanical properties, the wear resistance of the granular bainite-acicular ferrite muhiphase structure is the best, followed by the granular bainite-polygonal ferrite structure, and then the lath bainite-polygonal ferrite structure.
Abstract: M3 high speed steel (HSS) with or without niobium addition was prepared by spray forming, and the effect of niobium on the microstructure of M3 HSS was investigated by scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC) and optical microscopy (OM). Finer and uniformly-distributed grains without maerosegregation appear in the as-deposited HSS, and the addition of niobium tends to shift the precipitation of primary MC-type carbides to a higher temperature. Plenty of refined niobium-containing MC carbides precipitate as isolated sphere particles in the grain boundaries before onset of eutectic reaction. Niobium mainly appears in primary MC-type carbides by consuming carbon, which suppresses the degree of eutectic reaction to a large extent, leading to the decrease in both amount and size of M2C lamella carbides. The refined metastable M2C carbides in Nb-containing HSS can be completely decomposed easily during hot deformation, and the homogeneity of carbides in Nb-containing HSS is improved. The wear-resistant property of Nbcontaining HSS is superior to that of M3 HSS at a lower load or temperature. But this gap is reduced with temperature rise. The main reason is that the large number of refined primary MC carbides can improve the abrasive wear resistance of HSS, but have no effect on its oxidation resistance.
Abstract: Isothermal interrupted hot compression tests of FGH96 superalloy at the two-pass strains of 0.6 + 0.6 and 0.3 + 0.9 were performed on a Gleeble-1500 thermo-mechanical simulator. The hot deformation behavior and microstructural evolution of the superalloy were investigated in the deformation temperature range of 1050 to 1125℃ and the strain rate range of 0.001 to 0.1 s-1. It is found that recrystallization happens during the two-pass hot deformation, and less deformation in the first pass results in less cracks in samples. As the first-pass hot deformation is less, the recrystallization degree increases during the deformation gap with increasing deformation temperature and strain rate. An obviously change is found in the processing map with different strains or different two-pass strains. Under the same deformation condition, when the energy dissipation rate changes with strain, different microstructural evolution rules happen. When the energy dissipation rate decreases with increasing strain, the recrystallization grains coarsen; otherwise, the recrystallization grains refine. But when the energy dissipation rate does not change with strain, coarse grains appear with the energy dissipation rate lower than 20% or a fine grain microstructure appears with the energy dissipation rate higher than 35%.
Abstract: The mierostructure and texture evolution of Ti-6Al-4V alloy under different forging processes on a free forging hydraulic press were investigated by scanning electron microscopy, electron backscattered diffraction and X-ray diffraction. It is found that the microstructures of Ti-6Al-4V alloy under different forging modes, unidirectional forging and cross upsetting and stretching, are nearly the same. The distributions of ct phase and β phase in the difficult deformation zone, small deformation zone and large deformation zone are very similar, while the strain is distinctive in different forging regions. Further observations indicate that, in the edge region with small strain, the slip system is mainly the {0001} basal plane and forms the basal texture, {1120} and {1010} prismatic textures occur in the internal high strain region, while { 1122} and {1011} pyramidal textures appear in the place where the stress concentrates. The two forging processes can both improve the uniformity of deforming textures; in addition, cross upsetting and stretching is better than unidirectional forging.
Abstract: The effects of cold rolling and solution treatment on the texture and mechanical properties of Ti-26Nb-4Zr alloy plates were investigated by X-ray diffraction and tensile testing at room temperature. It is found that a {001}〈uvw> rolling texture appears after 50% cold rolling. With increasing cold rolling reduction, a {121}〈111> and {001} <110> mixed texture forms finally. The 〈110> direction turns from perpendicular to parallel to the rolling direction. After solution treatment at 800°, a {111} <110> recrystallization texture forms and its intensity increases with cold rolling reduction, while the (110) keeps parallel to the rolling direction. Due to work-hardening and refined crystal strengthening, the strength of the cold rolled plates increases while the plasticity decreases with the increase of cold rolling reduction. After solution treatment, the plasticity increases markedly because of the occurrence of recrystallization.
Abstract: Hydration reactions of samples made from skarn-type copper tailings, blast furnace slag, quartz sand, cement clinker and natural gypsum during the process of pre-curing, autoclaving and re-curing were investigated by strength testing, X-ray diffraction analysis and scanning electron microscopy. The influences of calcium and silicon contents on the amount and variety of hydration products generated in the reactions were analyzed and the effects of hydration products on the strength of the samples were discussed. It is found that the strength of autoclaved products in different curing stages depends on the amount and variety of hydration products generated in the curing process, while the amount and variety of them hinge on the amount and existence form of calcium and silicon.
Abstract: A solid surface frequency modulated continuous wave (FMCW) radar signal model was built to solve the range ambiguity problem of wideband and low signal-to-noise ratio (SNR) FMCW signal under severe measurement conditions. Based on prior information, a distanee inversion method was proposed, which contained signal pretreatment, band intercepting, and energy weighting. Actual data processing results show that the SNR of the frequency spectrum rises from-5.55 to 8.32 dB after pretreatment. The index of similarity of the stock level shape increases from 0.46 to 0.71 and 0.79 by band envelope interception and least squares interception, respectively.
Abstract: An optimization of flow control "devices in a 40-t single strand continuous casting tundish was carried out by water modeling experiments and industrial experiments. Three cases were considered during the experiments, i. e, tundish equipped with a turbulence inhibitor, tundish equipped with a turbulence inhibitor and dams, and tundish equipped with a turbulence inhibitor, dams and weirs. The results show that the dams play a much more important role than the weirs in improving the fluid flow characteristics and decreasing the dead volume fraction in the tundish. The average residence time increases firstly and reduces afterward with increasing distance between the dam and nozzle. The tundish equipped with a turbulence inhibitor and dams is the optimized according to these results, and the dead volume fraction reduces to 13.6% from 25.9%. The results of industrial application shows that the T. O and N contents reduce greatly and the mass fraction of macro inclusions in normal slabs reduced to 3.2×10-7 from 8.4 × 10-7.
Abstract: This article introduces the design of symmetrical approximately shift-invariant fractional overcomplete wavelet transforms. First, a design scheme for the symmetrical low-pass filter with minimum-length was proposed, and then the corresponding highpass filters with approximately shift-invariant properties were constructed via Toeplitz matrix factorization, which has a lower computational complexity than other methods. In addition, fractional overcomplete wavelet transforms could he designed with higher vanishing moments through the method proposed. Subsequently, a bearing fault diagnosis scheme was proposed using the symmetrical shiftinvariant fractional overcomplete wavelet transforms. Experimental results show that the bearing faults can be detected effectively using the symmetrical shift-invariant fractional overcomplete wavelet transforms.
Abstract: This article is focused on the non-smooth problem of the semi-supervised support vector machine optimization model. A smooth semi-supervised support vector machine model was established. A general cubic spline function with 2 times differentiable at zero point was deduced by a general three-moment method and was used to approach the non-smooth part in the semi-supervised support vector machine. A new smooth semi-supervised support vector with 1 time differentiable based on the general cubic spline function was constructed, and thus a lot of fast optimization algorithms could be applied to solve the smooth semi-supervised vector machine model. The approximation accuracy of the general cubic spline function to the symmetric hinge loss function was analyzed, and the convergence accuracy of the new model was proved. Numerical experiments show that the new model has a better classification result.
Abstract: An energy model of excess pore pressure generation under vibration loading was adopted to simulate the installation process of composite vibro-stone columns. The interaction between the energy dissipation and hole expansion was taken into account and a reasonable simplification was made in the simulation. The finite difference method was used to discretize the reinforced area and to solve the boundary value problem. A numerical program was developed to simulate the installation process of composite vibro-stone columns. The influence of wicks on the variation of pore pressure for composite vibro-stone columns was discussed in details. Finally, the reinforcement results were compared between traditional stone columns and composite vibro-stone columns. Numerical simulation indicates that the reinforced areas of composite vibro-stone columns are obviously lager than those of the traditional stone column duo to the existence of additional wicks. This reinforcement method is not only suitable for the sand ground but also valid for the silt or siltsand ground.
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
