Abstract: The success of the shale gas revolution in America largely depended on the breakthrough in the key technologies of horizontal drilling and hydraulic fracturing. Because of this, America's energy crisis was greatly relieved. With more and more people focusing on the exploration of shale gas and tight oil, the novel technologies on how to choose, calxy or transport fracturing proppants catch more and more attention. Three common kinds of traditional proppants (sands, ceramics and resin-coated sands) as well as the novel fracturing types (self-suspending, ultra-high-strength, ultra-light-weight and novel rod-shaped proppants) were reviewed. The future potential applications are explored and the analysis could be valuable for researchers and engineers to exploit unconventional oil and gas reservoirs in China. High-property, multi-function, mini-size and smart modification are predicted to be the primary development tread for proppants.
Abstract: Triaxial compression testing was performed on an MTS 815.03 rock testing machine and acoustic emission data were collected by using a DISP acoustic emission test system. An experimental comparison was done between rock mass specimens having a weak structure plane with steep dip angle and rock specimens. The strength of the two kinds of specimens gradually increases with the increase of confining pressure, and the failure mode changes from brittle to ductile. Sliding failure along the structural plane occurs in the rock mass, while shear failure in the rock. With the increase of confining pressure, the elasticity modulus, deformation modulus, peak strain and peak strength of the two kinds of specimens increase. Moreover, the elasticity modulus, deformation modulus, and peak strength of the rock mass are lower than those of the rock, but the peak strain is higher. The internal friction angle of the rock mass is lower than that of the rock, but the cohesive force is higher. With the increase of confining pressure, acoustic emission events in the peak stress stage are far more than those in the other stages, and the acoustic emission events of the rock mass are more than those of the rock. The results of study show that the weak structure surface results in the lower mechanical properties of the rock mass, so it is a key factor in site selection for a high-level radioactive waste geological disposal repository.
Abstract: Based on the self-made servo-controlled seepage equipment for thermal-hydrological-mechanical coupling of coal and rock, a loading and unloading experimental study was performed by increasing the axial compression and decreasing the confining pressure in consideration of the actual mining method. The mechanical characteristics and permeability evolution rule of coal were analyzed and studied under loading-unloading conditions. The results show that during the process of loading and unloading, the faster the loading rate of axial stress, the longer the platform of the stress-strain curve near the peak, and the larger the peak stress, axial strain and circumferential strain, while the smaller the volume strain. The deformation moduli at different loading and unloading rates exhibit the trend of rapidly decreasing first and then slowly decreasing. When damage occurs, the deformation modulus rapidly decreased and then is nearly constant. Under that condition of the same axial strain, the deformation modulus increases with the decrease of loading and unloading rate. The relations of deviatoric stress and coal permeability with strain can be divided into three stages in the whole test process:initial compaction and elastic stage, yield stage, and post-failure stage. During the process of loading and unloading, the slower the loading and unloading rate is, the larger the coal permeability and volume strain become when the axial stress of coal samples reaches the peak value.
Abstract: A model of cumulative blasting was established to study the mechanism of crack propagation and permeability increasing under cumulative blasting in a coal seam. The forming mechanism of shaped charge jet, the propagation characteristics of stress wave and detonation wave, the stress distribution characteristics of coal elements, and the mechanism of crack extension under cumulative blasting were investigated by theoretical analysis and numerical simulation. It is found that the propagation characteristics of detonation wave promote the forming of cumulative jet, and change the propagation characteristics of stress wave and the stress distribution characteristics of coal elements significantly. The stress peak values of coal in the major and minor cumulative directions are 1.10-1.29 times that of coal in the non-cumulative direction, and the stress peak value of coal in the major cumulative direction increases from 0.85 times that of coal in the minor cumulative direction to 1.06 times in the range of blasting effect, slowing down the attenuation rate of the stress peak value of coal and increasing the crack propagation velocity. Besides, field experimental results of cumulative blasting in a coal seam indicate that the average concentration of extracted gas after blasting is 1.58 times that before blasting, and cumulative blasting can promote crack propagation effectively.
Abstract: The effects of SiO2, Al2O3 and MgO on the hydration of lime were investigated by isothermal calorimetry, and the results were validated by 5 types of lime used in the sintering plant. It is found that the total hydrating heat of lime has positive relationship with CaO content, and decreases with increasing SiO2, Al2O3 and MgO contents. The contents of SiO2, Al2O3 and MgO also have important effect on the hydrating speed of lime. When the mass fraction of SiO2 increases to 1%, the hydrating speed of lime dramatically decreases, and then slowly drops with increasing SiO2 content. A small amount of Al2O3 has no significant effect on the hydrating speed of lime, but when the mass fraction of Al2O3 is more than 2%, the hydrating speed of lime sharply decreases. With the increase of MgO content, the hydrating speed of lime significantly decreases.
Abstract: To explore the coalescence, growth and settling behavior of metallic Fe droplets under the dynamic oxidation condition, the effects of oxidation time, air stirring intensity and pure oxygen oxidizing on the coalescence of metallic Fe were investigated in this paper. The changes in temperature and viscosity of the molten slag were studied during the dynamic oxidation process, and the settling speed of metallic Fe was calculated. It is indicated by lab and 1200 kg pilot-scale experiments that low valence titanium is oxidized by blowing the oxidizing gas. As the temperature increases, the viscosity of the slag decreases, which accelerates the coalescence, growth and settling of metallic Fe droplets. With a longer oxidizing time, low valence titanium and (FeO) finally almost vanish, and metallic Fe droplets are oxidized, resulting in the decrease of metallic Fe recovery. The judgment of the oxidation end point depends on the (FeO) and low valence titanium content.
Abstract: Slag oxidability, steel composition and inclusions were analyzed by slag sampling and steel sampling from the BOF endpoint to the tundish for studying the influence of ladle slag oxidability on the cleanliness of ultra low carbon steel. The results show that by ladle slag treatment after BOF tapping, T. Fe content in top slag decreases from 19.18% to 4.68% when getting in RH, indicating that the reduction of slag oxidability is obvious. The reduction of T. Fe content in slag leads to the reduction of[O] content in steel. For some heats with low T. Fe content, the average oxygen-blowing amount is large, and then the[O] content before Al deoxidization is relatively high. The relationship between the T. Fe content of RH end slag and the number of inclusions is linear, but meanwhile there is no obvious relationship between the number of inclusions after RH and the[O] content before Al deoxidization. The (CaO)/(Al2O3) ratio of ladle slag influences the Al2O3 absorption ability. The number of inclusions will be large if the (CaO)/(Al2O3) ratio of the slag is not reasonable. The defects of hot rolled sheets significantly decline with the reduction of slag oxidability.
Abstract: Nitriding reaction of Mn pellets prepared under different conditions was investigated with a self-made air-proofed nitriding system. The effects of Mn particle size, pelletizing pressure and binder content on the nitriding reaction were studied, and the real-time variation curves of temperature and Mn pellet mass were measured. The results show that with the decrease of particle size from 16-40 mesh to 60-80 mesh, the time for the pellet center temperature reaching peak (tp) shifts from 164s to 101 s, the maximum temperature increment at the pellet center (ΔTmax) increases from 147 ℃ to 233 ℃, and the conversion ratio at 1 h rises from 90, 81% to 93.64%. With increasing pelletizing pressure from 266 MPa to 443 MPa, tp decreases by 89 s, ΔTmax increases by 22 ℃, and the conversion ratio at 1 h rises from 91.59% to 94.92%. With the increase of binder addition from 1 g to 3 g, the conversion ratio at 1 h drops from 92.90% to 89.80%. The data points of the conversion rate and the nitriding time can be approximately fitted with the probability density function of the log-normal distribution.
Abstract: The effect of cooling intensity on the carbide segregation and solidification microstructure of an H13 as-cast ingot with Mg addition was studied during the electroslag remelting process. The solidification microstructure and the carbide characteristics of the steel were analyzed by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analysis. The results show that the solidification microstructure of the ingot consists of martensite, retained austenite and primary carbides. Carbides in the electroslag remelting ingot are V8C7, MC, M23C6 and M6C. With the increasing of cooling intensity, the size of carbides in the edge of the electroslag remehing ingot decreases, the distribution of these carbides becomes more homogeneous, but the types of carbides remain unchanged. Increasing the cooling intensity improves the modification of inclusions by Mg. The formed MgO. Al2O3 arising from Mg treatment provides preferred nucleation sites for TiN. These complex inclusions promote the heterogeneous nucleation of primary carbides, consequently refining primary carbides.
Abstract: To solve the detection problems of slab surface defects by conventional image recognition algorithms, this article introduces an improved multi-block local binary pattern algorithm which considers the image's pixels. In this algorithm, the original image is divided into several small regions, each small region is equally divided, and the average gray value is calculated. Then the local binary pattern algorithm is used. Five different kinds of 1697 samples gathered from a production line of slabs were examined, including cracks, scratches, indentations, dents, and no defect. The recognition rate reaches 94.9%, while the recognition rate of the traditional local binary pattern method is 89.1%. The results show that the proposed algorithm has the characteristics of high precision, better robustness and noise immunity.
Abstract: For 12-ram-thick hot-rolled X70 pipeline steel strips coiled at 500 ℃, a coupled thermomechanicalphase transition model in the laminar cooling process was established by MARC finite element software, and then the changes in temperature field, stress, strain, volume fraction of phase transformations and warping degree in the duration of laminar cooling were calculated at two kinds of cooling water ratios. The results show that the maximum warpage of the strip edge is 21.84 mm because of different strain values of the upper and lower surfaces resulting from different cooling rates in the thickness direction in the early stage of water cooling at a water ratio of 1.25. The steel plate will gradually restore straight in the later cooling process. However, the warpage of the strip edge is still -9 mm at the beginning of coiling due to the plastic deformation in water cooling and the different bainite contents in the thickness direction at finishing cooling. Uneven cooling between the upper surface and the lower surface is the fundamental reason of warping. Under the condition of ensuring the performance of X70 pipeline steel, the residual warpage of the strip edge is only -0.58 mm at the beginning of coiling when the water ratio is adopted to be 1.58. The proper water ratio can greatly reduce the strip's transverse warping in the laminar cooling process.
Abstract: The isothermal transformation kinetics of experimental steel was studied by the thermal expansion method. Uhrafine bainite was obtained by austempering at low temperature. The microstructure was quantificationally analyzed by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that microstructure of the experimental steel is composed of a large number of uhrafine lath bainite ferrite and thin film austenite. The spacing of the bainitic lath is about 60 nm and the hardness is about HBW 610 by austempering at 210%. The final microstructure and properties depend on the temperature and holding time for austempering. The holding time for fully transformed bainite increases at a lower austempering temperature.
Abstract: A self-made gas-solid erosion testing apparatus driven by shock wave was used to investigate the wear properties of 1Cr9Mo steel commonly used as manufacturing materials in the coal chemical industry, and SiO2, Al2O3 and SiC particles were chosen as erosive particles. Combined with the surface morphology analysis of eroded specimens, high-speed erosion wear characteristics were studied under different conditions involving impact velocity, impact angle, particle hardness, particle size, and specimen temperature. The results show that when the temperature is 20 22 and 400 22, the erosion rate of 1Cr9Mo steel reaches its maximum value within an impact angle range of 15° to 25°, and the wear properties are characterized as ductile metal. At low impact angles the cutting of particles is the main mechanism; but at large impact angles the erosion mechanism is the exfoliation of platelets around the pits from the material surface, which is produced by the vertical impact of particles to the material surface. When the velocity exponent of 1Cr9Mo steel ranges from 2.3 to 3.2, the erosion rate is much dependent on particle hardness. Under the same erosion conditions, the erosion rate caused by Al2O3 and SiC particles is an order of magnitude higher than that caused by SiO2 particles for they have higher hardness values. With the increase of particle size, the erosion rate increases first and then falls. The erosion rate caused by SiO2 particles at 400 ℃ increases significantly, and the maximum erosion rate is 3 times as large as that at 20 22.
Abstract: In order to improve the thermoplasticity of lean duplex stainless steel, the precipitation law and mechanism of lean duplex stainless steel 2101 (LDX2101) and duplex stainless steel 2205 (DSS2205) were studied in hot rolling. It is found that LDX2101 is susceptible to nitride precipitation at phase boundaries compared with DSS2205, which causes microcracks and results in the thermoplasticity of specimens worsen. According to relevant thermodynamic data, the equilibrium solid solubility formulas of Cr2N precipitation in LDX2101 and DSS2205 were deduced, and total solid solution temperatures of Cr2N precipitation were calculated through Thermo-Calc software and experimental data. Meanwhile, the Wagner interaction coefficient was introduced to consider the influence of Ni, Mn, Mo and Si on the equilibrium solid solubility product formula. The results show that the total solid solution temperature of Cr2N precipitation in LDX2101 is around 100 ℃ higher than that in DSS2205. The calculation results and experimental results are in good agreement. The finishing hot roiling temperature must be above the total solid solution temperature in the practical production process to prevent Cr2N precipitation. Otherwise, the nitride precipitation is prone to produce at phase boundaries, which influences the thermoplasticity of the materials.
Abstract: The effects of no light, half-day light and all-day light on the corrosion behavior of Q450NQR1 weathering steel in the wet-dry cycle condition were examined by corrosion mass loss, scanning electron microscopy, X-ray diffraction and linear polarization tests. The results indicate that light significantly affects the corrosion process in the wet-dry cycles. In the early stage of steel corrosion (before 48h), the corrosion rate from fast to slow is followed by half-day light, no light, and all-day light; but in the later period (72-96 h), the corrosion rate is ordered by half-day light, all-day light, and no light. The corrosion morphologies are obviously different. The corrosion products are silt-shape distribution in no light condition and particulate distribution in light condition, while they are particle-distributed with finer particles and smaller pores in all-day light condition. X-ray diffraction results show that the corrosion products are the same, but the contents are different in the three conditions. By linear polarization tests, the polarization resistance is obtained in the order from fast to slow of no light, half-day light, and all-day light at 96 h, which is well consistent with the order of corrosion mass loss rate.
Abstract: To study the reaction characteristics of iron-based oxygen carriers, a one-dimensional mathematical model was developed for the reduction process of iron-based oxygen carriers in moving beds based on the unreacted shrinking core model. In this model, the multi-stage reduction between iron-based oxygen carriers and H2/CO was considered. The average error of gas species concentration between the simulative and experimental values is 6.92%, and the average error of reduction is 11.16%. The results show that the final reduction rate of iron-based oxygen carriers is about 23%, with the main reactions including the first-stage reduction and the second-stage one, whose reduction rate is 95% and 40%, respectively. A higher reaction temperature, suitable diameter of oxygen carrier particles and suitable gas-solid ratio are helpful to improve the depth of reaction and enhance the utilization efficiency of syngas and iron-based oxygen carriers. The recommended particle diameter is 1 to 2 mm.
Abstract: For violent vibration of the sink roll device of a hot-dip galvanizing line, an incomplete liquid-solid coupling method based on the wet modal was studied, the vibration modal of the device was numerically simulated, the natural frequencies and vibration modes were discussed, and the vibration test was performed. The partial mode of the sink roll changed the assembly relationship in bearings, and the clipping appeared in the time domain waveform of measured signals, indicating that crashing and friction existed in the sliding bearings. The frequency of the peak in the amplitude spectrum was 45.05 Hz, close to the fourth order frequency and mode, which showed that the fourth order natural vibration of the device was dominant. The double-frequency vibration was caused by nonlinear vibration of liquid-solid coupling. The main cause of sidebands near the peak in the amplitude spectrum came from the continuous action of the zinc liquid flow field. The numerical analysis and experimented research have significant correlation, and the incomplete solid-liquid coupling method can be effectively applied to engineering practice.
Abstract: In order to implement straight-line trajectory tracking control for unmanned parafoil vehicles (UPV), a variable-gain robust backstepping control method was proposed based on a simulation object. A variable-gain baekstepping tracking controller was designed against the trajectory tracking error model, and proper design of gain parameters eliminated a part of complicated nonlinear terms and avoided higher derivatives in traditional backstepping methods so as to make the controller simpler and to be beneficial to engineering realization. The robust feedback compensation term designed according to the Lyapunov theory improved the system's robustness while ensuring its stability. In addition, the controller was applied to UPV planar straight-line trajectory tracking control. The simulation experiment illustrates the good robustness of the proposed controller and the accurate tracking ability in straight-line trajectories.
Abstract: A support vector data description (SVDD) was proposed to be introduced in the monitoring, diagnosis and optimization of processes. Firstly, the SVDD monitor model was established to obtain the control limit based on normal samples. Then, the contribution chart was used to diagnose outliners exceeding the control limit in statistics to find the main causes of abnormal production. Finally, the process parameter optimization was performed by the adjacent point replacement. The proposed method was applied to the process of cold rolled sheets. The results show that this method has a higher detection rate than traditional T2 PCA during the production process monitoring, and can optimize the process parameters to make it return to the controlled state.
Abstract: To overcome the defects of the depth estimation of buried structures by the empirical method, a new method to estimate the depth based on the reflected waveform characteristics of buried targets was put forward by extracting few points from the reflected waveform. Accuracy analysis was performed in consideration of waveform distortion. The resuhs show that on ideal undistorted ground penetrating radar (GPR) data, the proposed method is accurate in estimating the depth and the horizontal position of buried targets, as well as the electromagnetic wave speed. An average error of 55.202% occurs in depth estimation based on distorted waveform data even though the estimation result of wave speed is accurate as before. So the method is corrected to confirm the depth of buried targets using the estimated wave speed and the two-way travel time of the reflected wave from the structures when facing distorted GPR data, and the accuracy of estimation satisfies the requirements of the GPR method. This method is more satisfactory and robust compared with the empirical method.
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
