Abstract: This paper summarizes current developments and ongoing research of MgO-C bricks, both at home and abroad, and especially analyzes antioxidant and low-carbon aspects. A future research direction regarding MgO-C bricks was proposed based on the discussion. Specifically, the property improvement of traditional MgO-C bricks through component optimization and structural design, the development of a new antioxidant, improvement of MgO-C bricks in low-carbon methods, and evaluation of corresponding properties, were proposed.
Abstract: Prediction and prevention of rock burst in project is difficult because of its paroxysm and sudden destructiveness. Determining how to predict the time, place, and intensity of rock burst is one of the main engineering problems that must be solved via geotechnical engineering. Increasing number of experts from the field of underground mining and construction are applying new monitoring techniques and methods to study rock burst for its effective prediction. In the model experiment, the entire process of structuretype rock burst was remotely monitored via the laser Doppler vibrometer. Based on the dynamic theory and energy conservation law; the natural vibration frequency was used to analyze the elastic coefficient of the shear plane. The experimental results show that the incompatible weakness of structural plane is a necessary condition for the occurrence of rock burst, and the spatiotemporal difference of the structural plane strength is the main factor that determines the immediate or the time-delayed rock burst. Slow weakening of the structure causes time-delayed rock burst, whereas rapid weakening causes immediate rock burst. During the whole process of rock burst, the weakening rate of rock mass structure is determined using the natural vibration frequency, and the dissipated energy of the structure occupies merely 0.06% of the rock elastic energy. Thus, most of the elastic energy is released in the form of kinetic energy, and the rock is ejected with high velocity. Furthermore, the incompatible weakening characteristics of rock burst structural planes can be analyzed using the analysis of the frequency decline rate. Therefore, the new monitoring index of dynamic characteristics such as natural vibration frequency improves the understanding of evolution characteristics of rock burst and plays a significant role in the early warning of rock burst in underground engineering.
Abstract: In the vibration based structural health monitoring (VBSHM) field, the modal frequency of a structure is commonly used as an indicator for the global health condition of the structure. However, field measurements have shown that the modal frequency of a bridge varies with structural anomalies and the operational and environmental actions, e. g., temperature and traffic loading. Moreover, the latter variation usually exceeds the frequency shifts induced by the small and medium structural anomalies. To highlight the anomaly-induced frequency changes, the variability of modal frequencies of bridges with the operational and environmental actions must be investigated, and then, the action-induced frequency variations need to be eliminated. According to the periodic characteristics of the six-year monitoring data of the Donghai Bridge, this research identified the main actions that affected the modal frequencies of the first vertical/lateral bending modes and torsional mode of the girder of this bridge, and further, it compared the relative contributions of actions to the variability of frequencies through the partial correlation coefficients and the proposed cyclic averaging method. The results show that the modal frequencies of the Donghai Bridge vary at cycles as 1 a, 1 week, 1 d, and 12.42 h, which coincide with the inherent predominant cycles of structural temperature, traffic loading, wind loading, and sea levels, respectively. Structural temperature and traffic loading are the most influential factors for the frequency variation, and their relative importance is different for each individual cycle. The results also show that the cyclic averaging method can effectively separate the components in periods of 1 a, 1 week, and 1 d and can disclose the inherent correlation between actions and modal frequencies. This study helps in enhancing the understanding of the frequency variability for operational bridges and may lead to a more reliable evaluation of structural performance.
Abstract: Notable contributions to our improved understanding of jacked pile behavior in sand have been achieved through instrumented model pile tests in laboratory test chambers, at elevated g-levels in the centrifuge, and in the field. In recent years, research focusing on pile behavior in clay has declined. Consequently, predictive methods for pile capacity have not advanced beyond those provided in American Petroleum Institute (API 2000) recommendations, which were based on research conducted in the early 1980s. This paper re-focuses attention on the shaft capacity of jacked piles in clay. Three centrifuge scale pile tests were performed in kaolin clay in the drum centrifuge at the University of Western Australia. The tests were performed in pre-consolidated blocks of kaolin, and were subsequently spun in the centrifuge at three different g-levels of 50g, 125g and 250g respectively. The piles were equipped with total pressure sensors located at different depths and were installed by jacking into samples of reconstituted kaolin clay. The kaolin clay samples were prepared to measure the range of the cone penetration test end resistance (qt), undrained strengths (su-Tbar), and overconsolidation ratios (OCRs). These pile tests were used to investigate the lateral stress changes (σr) developed along the pile shafts during pile installation and equalization. In addition, the change in the value of lateral stress (Δσr) and the changes in pile shaft resistance during the pile tension test were discussed. The characteristics of the jacked pile in the clay with different over-consolidation ratios (OCRs) were revealed. Furthermore, the centrifuge data were subsequently used to examine the current design methods for the evaluation of the shaft capacity of displacement piles in clay. The centrifuge test results show that during the pile penetration, a strong dependence of lateral stress on the relative depth of the pile tip (h/B) develops, and the total radial stress, as measured in a particular soil horizon, is observed to decrease as the relative depth of the pile tip (h/B) increases (where h is the height of the sensor above the pile tip, and B is the diameter of the pile). Based on the cone penetration test during the investigation, it is observed that the lateral stress developed on a displacement pile is strongly depended on the cone penetration test end resistance (qt) and the relative depth of the pile tip (h/B). It is shown that the empirical method allowing for a dependence of shaft friction on qt, and h provides good estimates of the shaft capacities measured in centrifuge experiments. The research results have certain theoretical and engineering significance for pile construction and bearing capacity design in the soft soil region.
Abstract: Due to the rapid construction of tunnels in China, problems that are associated with both quality and safety have become apparent. Therefore, the control and treatment of various tunnel defects are gradually becoming a primary focus during both construction and operation of tunnels. Further, a ground penetrating radar (GPR), which is based on the ultra-high frequency pulse electromagnetic wave theory, provides advantages such as efficiency and convenience. Further, GPR has been extensively used to perform nondestructive detection of tunnel defects in order to ensure sufficient quality and safety. To improve the efficiency and reliability of the GPR detection process, a novel method that identified tunnel defects using the GPR images in an intelligent manner was proposes based on the multidimensional analysis of GPR reflections. Six typical identifying features of defect signals were initially extracted based on time domain, frequency-domain, and time-frequency domain analyses. Further, automatic identification of the horizontal distribution of the defect was obtained by searching for all the defect signals using a classification model constructed by a support vector machine, which was used for training the model with the typical features. Furthermore, by calculating the depth distribution of defects according to the first intrinsic mode function (IMF1) component envelope of the defect signals, intelligent identification of tunnel defects can be achieved. A comparison between the results of the intelligent and artificial identification mechanisms when applied to a tunnel backfill measured GPR data depicts that the intelligent method illustrates a strong ability to identify defects in GPR data. Further, only a few errors are produced:the identification rate and accuracy of test data are 100% and 78.6%, respectively, which satisfies the engineering application requirements. This method can be used to intelligently identify the defects in different types of GPR data in tunnel engineering. Furthermore, the results of this study can provide some hints about the design of intelligent identification algorithms that can be applied in other areas of GPR detection with various detection target types.
Abstract: In geotechnical and mining engineering, numerous particle matters are involved in scientific and technical problems. Recognition and quantification of the structure and distribution of force chain networks using photoelastic experiments, for instance, are significantly important in understanding the internal mechanism of mesoscopic mechanics and studying the macroscopic mechanical behavior. Based on the algorithm of the mean square value of color gradient (G2), the correlations of G2 with the contact force (F) of different sizes of round and square particles were established and combined with digital image processing technology. A method was proposed for identifying particles in images and distinguishing square particles from round ones, and force chain structures and force chain distributions were obtained in photoelastic images. Using fully mechanized caving mining as an example, the proposed method was verified, and it elaborated the formation and characterization of mining-induced stress in a top-coal caving mining face. The study shows that F monotonically increases with increased G2, and larger particle sizes correspond to a faster growth of F. The contact forces of singular particle distribute primarily between 0.5 and 1.5 times average contact force. Also, the average contact forces in square particles and Φ12 mm circular particles are higher and mainly occur in strong force chains, whereas average contact forces in Φ10 mm and Φ8 mm circular particles are lower and primarily occur in weak force chains. In top-coal caving mining, force chains in top-coal and overburden strata are mainly displayed in tree-like forms. Strong force chains, which extend in a vertical direction, transmit majority overburden loads, whereas lateral-developed weak force chains play a role in supporting strong force chains. In the vicinity of the top-coal outlets, because of the lateral movement of particles toward the mined area, the weak force chains in top coal disappear, resulting in the strong force chains becoming weaker or completely disappearing.
Abstract: Magnetic coating magnetic separation method was proposed to separate pentlandite from serpentine, which is difficult to separate them using flotation. Results show that under certain physical and chemical conditions of slurry, the pentlandite recovery increases with the amounts of magnetite increasing, while the recovery of serpentine remains at a low level, indicating that their separation could be realized. The separation results of the artificial mixtures show that with addition of 5% magnetite, a concentrate of 19.89% Ni with a recovery of 92.46% and MgO mass content of 4.72% are obtained. The results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrate that quantities of magnetite particles adhere to the pentlandite surfaces whereas the surface of serpentine is not clearly coated by the magnetite. The Zeta potential analyses and DLVO calculations suggest that with the addition of sodium hexametaphosphate (SHMP), the Zeta potential of serpentine reverses from positive to negative while those of pentlandite and magnetite are not affected significantly. Thus, it made the interaction of magnetite-serpentine become repulsion while that of magnetite-pentlandite remain attraction. Consequently, magnetite particles selectively adhere to the surface of pentlandite and enhance its magnetism, resulting in the magnetic separation of pentlandite from serpentine.
Abstract: Sinter ore is one of the main materials of blast furnaces in China, and the productivity of the blast furnace and the economic and technical indicators of the ironmaking process are directly influenced by sinter yield and quality. Therefore, the ore-blending process should be optimized based on the high-temperature characteristics of iron ore to improve the sinter yield and quality and the energy efficiency of the ironmaking process. The liquid phase fluidity of iron ore is a vital characteristic of high-temperature sintering, since a suitable liquid phase fluidity of blended ores produces a sintered body with a stronger bonding strength. In this paper, by simulating the contact state of the iron ore particles and the calcareous flux particles in the actual sintering adhering fines, the FactSage thermodynamic calculation and the visible micro-sintering tests were conducted to study the liquid phase fluidity indexes of different iron ores and the major melt formation characteristic factors that influenced the liquid phase fluidity of iron ore under fixed CaO ratio conditions. The results show that the rule of liquid phase fluidity of iron ores under a fixed CaO ratio is different from the rule of liquid phase fluidity of iron ores with fixed alkalinity. According to the fitting relationship between the calculation results by Factsage software and the testing results of liquid phase fluidity index of the 9 kinds of iron ores, the formed melt content of iron ore is the most important melt formation characteristic factor that affects liquid phase fluidity. The formed melt content and the liquid phase fluidity index are directly related, and the coordination mechanism of liquid phase fluidity of iron ore is based on the principle of linear superposition of the formed melt content. Furthermore, the content of gangue minerals affects the liquid phase fluidity of iron ore to some extent. The liquid fluidity index decreases greatly with increased SiO2 content, leading to lower formed melt content, while the liquid fluidity index slightly increases with increased Al2O3 content.
Abstract: Coal is one of the most important energy sources in our society. However, there have been increasing environment concerns regarding coal utilization. The high-value application of low-rank coal has an important significance for broadening the energy pathways, improving energy efficiency, and solving environmental problems. In this study, thermal dissolution coals (TDCs), which have low ash and high volatility, were extracted from four types of low-rank coal by N-2-methyl-2-pyrrolidinone (NMP). The combustion characteristics of TDCs were investigated by thermogravimetric analysis, and the structure variation law of raw coals and TDCs were compared using Raman spectra. The results show that the ash content and fixed carbon of TDCs significantly decrease, whereas the volatile content and high heating valve increase. The H/C atomic ratios of KL, GD, and ZS TDCs are higher than those of raw coals, whereas XB has a lower H/C atomic ratio than that of raw coal. The ratio of peak intensity (ID/IG) and peak area (AD/AG) values of KL, GD, and ZS TDCs are greater than those of raw coals, indicating that as the ordering degrees of these TDCs decrease, the structure deficiencies and combustion reactivity increase. In contrast, XB coal showed opposite results.
Abstract: The preparation of ceramic materials is a new way of utilizing steel slag. It is important to investigate the influence of different sintering atmosphere on steel slag ceramics, which is of great significance in promoting the application of steel slag ceramic technology. In this paper, 20% of steel slag and 80% of clay were used as the main raw materials under different atmospheres, namely, air and nitrogen, and were prepared into steel slag ceramic bricks. The ceramic bricks'crystal phase evolvement and performance were analyzed, and the effect of partial oxygen pressure on the oxidation of Fe2+ in the steel slag ceramics was investigated quantitatively. The results show that under air conditions, the Fe2+ in raw materials is oxidized to form the hematite phase, and the compressive strength and water absorption of sintered samples were 310 MPa and 3.7%, respectively, which is better than those of sintered samples under nitrogen conditions. Under nitrogen condition, the Fe2+ in the raw material is kept unchanged to form hercynite and pyroxene, and the size and quantity of pores in the sintered samples are greater than those under air conditions. This contributes to its poor mechanical properties. The critical range of the oxygen's partial pressure for the transformation of Fe2+ and its crystals is 0.5% -0.75%. When the partial pressure is less than 0.5%, a black or brown ceramic sample can be obtained and is mainly composed of hercynite and pyroxene. When the partial pressure exceeds 0.75%, Fe2+ begins to oxidize to Fe3+, hematite begins to form gradually, and its color changes from a brown or brownish red color. Increasing oxygen partial pressure in the sintering environment is an effective way for avoiding black core in the sintered steel slag brick.
Abstract: A 3D semi-cylindrical physical model of COREX shaft furnace was established, and the initial position and evolution process of dust accumulation in the bustle pipe of a shaft furnace were investigated through this model. The effects of discharging rate, gas flow rate, and non-normal operation condition on dust accumulation in the bustle pipe were also studied. The results show that the initial position of dust accumulation in the bustle pipe is in the 8#-12# slot region, located before the supporting tube of AGD beam. The dust blockage is first formed in the packed bed near the slot and then blocks the slot and grows into the bustle pipe if the growth velocity of the blockage region is greater than the descending velocity. Finally, dust accumulation can be observed in the bustle pipe. The dust accumulation is still growing in the bustle pipe, and the edge of the dust pile could develop to the far side; thus, the other slots would be gradually clogged by dust. Moreover, the results confirm that with increased discharge and gas flow rates, dust accumulation in the bustle pipe is greatly hindered. In contrast, under non-normal operation conditions, the dynamic balance of dust blockage is broken, and dust accumulation in bustle pipe is easily formed.
Abstract: To study the surface integrity of 20CrMnTi gears for form grinding by a microcrystalline corundum wheel, a grinding experiment on 20CrMnTi gear was performed. Furthermore, the effects of wheel speed, axial feed rate, and radial feed on tooth surface roughness, hardness, microstructure, and residual stresses of the surface/sub-surface were studied. The mechanism of the damage caused by grinding and micro-cracks was discussed. The results show that the effect of radial feed on the surface roughness is the most significant. The wheel speed is then the second most significant, and the axial feed rate is the least significant. In addition, an excessive grinding temperature leads to grinding burns, which the quenching burns cause the surface hardness to increase by 5% -20%, and the tempering burns cause the surface hardness to drop by varying degrees. The surface/subsurface structure is composed of a white layer, dark layer, and bulk material, with the white layer on the top and the bulk material being on the bottom. The white layer is composed of a dense martensitic structure, carbide, and retained austenite. The increase in the wheel speed and radial feed then increases the residual tensile stress caused by grinding. Surface residual compressive stress decreases and gradually changes to tensile stress. When the final residual tensile stress is greater than the breaking strength of the material, the surface produces micro cracks, compromising the integrity of the surface.
Abstract: The effect of SO42- on the passive and pitting behavior of 316L austenite stainless steel was investigated in a Cl--containing solution using potentiodynamic polarization tests, electrochemical impedance spectroscopy tests, potentiostatic polarization tests, and galvanostatic polarization tests. In addition, scanning electron microscopy was used to observe the pitting morphology. The results show that the increased SO42- concentration increases the passive region of 316L, makes the pitting potential more positive, and decreases the current density, indicating an improved pitting resistance. However, the pitting morphology shows a more complicated trend, and the roughness of the pits increases with the increased SO42- concentration after pitting occurred.
Abstract: Electrohydrodynamic jet 3D printing is an emerging and promising technology of microand nano-scale additive manufacturing with a low cost and high resolution, as well as a wide range of printed materials. However, due to the high printing speed and small standoff height between the nozzle and the substrate, it is especially difficult to directly observe and measure the printed patterns. Furthermore, there are many process parameters that affect the printing accuracy and quality, among which each parameter is coupling and interacting. This paper proposed a method of controlling the accuracy and quality of printed patterns based on the regulation of the shape and size of the Taylor cone by varying the process parameters. A theoretical model was then derived and established that describes the relationship between the line width printed with process parameters, printed material, and used substrate. Through the systematic experimental study, the influences and rules of the printing process parameters on the Taylor cone and printed patterns were revealed; Furthermore, the ideal jet printing window for the same nozzle was optimized. Finally, the feasibility and validity of the experimental results were demonstrated by the typical engineering cases, and a pattern of minimum line width of 3 μm was achieved with the nozzle diameter of 60 μm. The proposed method and experimental results provide a basis for further improving the accuracy, quality, and stability for electrohydrodynamic jet 3D printing, and the method offers a feasible solution for simplification and easy operation of actual 3D printing.
Abstract: In both Eye-in-Hand and Eye-to-Hand robotic visual controls, problems such as limited field of view or tracking target loss remain. Thus, online measurement cannot be performed within a certain distance and a certain degree, and a closed-loop control cannot be constructed. Based on Eye-in-Hand visual control and the theoretical shortest measuring distance Lmin, a visual servo combining the closed-loop and open-loop controls was proposed. When above Lmin, an iterative compensation method was proposed to adjust the attitude with the online measured data. In contrast, when below Lmin, a feed-forward compensation for relative linear motion was integrated to improve the positioning accuracy, estimating the error by the data determined by actually moving the path of the robot record by the visual system. As shown by several experiments, this method can effectively enhance the position accuracy.
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
