Abstract: In order to further study the failure mechanism of deep rock mass under the dynamic effect of excavation and blasting,the deformation characteristics,energy laws and failure model of skarn were investigated for the first time under the medium to high strain rate and the combined action of high static stress and frequent dynamic disturbance with an experimental system of coupled static and dynamic loads based on the SHPB device. The results show that the elastic modulus of rock increases with the increase of impacts and then it decreases,at the same time,the maximum strain exhibits an overall trend of decreasing first and then increasing. The elastic modulus drops sharply and the maximum strain shoots up when the last impact comes. The energy consumption per volume of rock is negative,which indicates that the rock samples exhibit a characteristic of energy release under impact dynamic action because a great much elastic strain energy stored in rock samples under high static stress action is released by the disturbance of impact dynamic action. The energy release per volume of rock increases first and then decreases with the increase of impacts. The skarn samples which have compact structure and high strength show a failure mode of splitting.
Abstract: The effects of early-age frozen pressure,negative temperature,and early-age load and negative temperature coupling on the strength,chloride diffusion and acoustic emission characteristic of freezing shaft wall C60 concrete were studied,and the internal microcracks were analyzed by scanning electron microscopy(SEM). It is found that the earlier the early-age load applies,the greater effect it has on the 28 d compressive strength of the concrete. But when the external load is applied 3 d later and the load level is less than 40% of the day's strength,the 28 d compressive strength of the concrete is almost not affected. A negative temperature environment of the freezing shaft wall can delay early concrete hydration,and antifreeze speeds up the development of concrete hydration and strength. Under the early-age load and negative temperature coupling effect,the 28 d compressive strength and durability of the concrete decrease,the chloride diffusion coefficient increases apparently,the concrete permeability changes from middle to high,the internal microcracks and deficiencies lead to advancing the active phase of acoustic emission,and the concrete presents apparent plastic deformation.
Abstract: To achieve good indoor living environment,improve the quality of staff living environment in refuge chambers and provide a basis guidance of design for the future,based on numerical simulation software FLUENT,the survival area under the way of air pressure supply was used as a research object,the main disturbance source was analyzed,and a three-dimensional model was set up with two kinds of air pressure supply pipelines. Air distribution in refuge chambers was visualized through the control equations,the RNG k-ε turbulence model and the finite volume discrete method in combination with SIMPLE algorithm. In the condition of air pressure supply,the layout of a uniform gas pipeline with nine air holes was determined as the optimal design scheme,and the volume fraction distribution regularities of oxygen and carbon dioxide were obtained. The feasibility of this numerical simulation was verified with field test.
Abstract: In order to effectively enrich phosphorus in converter slag,phosphorus enrichment was studied by TiO2 modification,the TiO2 modification process was discussed according to thermodynamic analysis,and the phosphorus-rich phase was separated from experimental slag by magnetic separation. It is found that CaSiTiO5,CaTiO3 and high phosphorus solid solution(n'C2S-C3P) form by a continuous reaction of n2CaO·SiO2-3CaO·P2O5(nC2S-C3P for short,n>n') solid solution precipitated in the slag and TiO2at 1623 K. The early precipitated solid solution(nC2S-C3P) decreases with the increasing TiO2 content,even disappears. If the addition of TiO2 increases or is excess in the slag,the high phosphorus solid solution(n'C2S-C3P) that forms by the above mentioned reaction will continue to react with TiO2 to produce CaSiTiO5 and CaTiO3,and then phosphorus content in the phosphorus-rich phase increases.Through magnetic separation under a magnetic flied intensity of 350 mT,the amount of collected non-magnetic substance in the slag modified by TiO2 increases by 23.84% compared with the original slag,the distribution ratio of P2O5 enlarges from 0.96 to 2.92,the amount of separated non-magnetic substance is 65.43% of the total of the modified slag,74.46% of phosphorus in the modified slag is entered into collected non-magnetic substance,and thereby most phosphorus is recycled.
Abstract: Lead citrate was prepared by the reaction of lead oxide and citrate. The effects of dissolution time,dissolution temperature,sodium citrate concentration,and the addition amount of citric acid on the dissolution rate of lead citrate in sodium citrate solution were investigated. Experimental results show that,dissolution temperature,sodium citrate concentration,and the addition amount of citric acid are the main influencing factors. Increasing the dissolution temperature or the sodium citrate concentration can significantly improve the dissolution rate of lead citrate. The dissolution rate of lead citrate has a positive linear relation with the dissolution temperature,and the fitted linear equation is Y=0.76 + 0.63T. Adding citric acid can inhibit the dissolution of lead citrate.
Abstract: Characterization of TiN precipitation during Ti-IF steel solidification was analyzed by thermodynamics and the solidification segregation model. It is found that TiN inclusions cannot precipitate in liquid steel before solidification. In the earlier stage of solidification,TiN precipitates at low temperature in solidified steel. When the solid fraction reaches to 0.64,TiN can precipitate in solid steel around the solidification front at higher temperatures,due to the increased enrichment of Ti and N. However,at the end stage of solidification,TiN can not only precipitate in solidified steel,but also in molten steel,for the segregation of Ti and N is getting serious. TiN distribution in the Ti-IF slab was observed by scanning electron microscopy(SEM). The results show that the number and size of TiN precipitates vary a lot from the slab surface to the center. The TiN size is increasing from the slab surface to the center,from 1-2 μm to 5 μm,and it is maximum in the area of 70 to 80 mm from the slab surface. In the middle of the slab in thickness,the TiN size is large,with an average size of 5 μm; while in the center of the slab,the TiN size is getting smaller again,with an average size of 3 μm. The TiN denseness is high in the surface layer of the slab,but decreases significantly in the center and middle. The precipitation moment,the size and number of TiN precipitates are closely related with the segregation of Ti and N and the solidification rate.
Abstract: In situ tensile tests in a scanning electron microscope(SEM) were carried out using single-edge notched specimens for two types of steels:a pure high-strength steel(HSS) composed mainly of ferrite and a small amount of pearlite,and a wheel steel composed mainly of pearlite and a small amount of proeutectoid ferrite. Regardless of the specimen thickness meeting the plane strain condition or not,the process of deformation and cracking for the pure HSS starts at ferrite slip,then continuously propagates and finally results in ductile fracture; the small amount of pearlite has nearly no impact on the overall deformation process; and the fracture surface is composed of dimples. However,for the wheel steel,when the specimen thickness is thin,which means that it does not meet the plane strain condition,plastic deformation occurs firstly in proeutectoid ferrite,even though its amount is very small,and then microcracks initiate and grow along the interface of proeutectoid ferrite and the pearlite colony,and finally evolves into discontinuous microcracks. The fracture surface fractograph presents both dimple and quasi-cleavage characteristics. For a wheel steel specimen with the thickness meeting plane strain condition,plastic deformation and cracking mainly occurs in the pearlite colony,which results in cleavage fracture.
Abstract: The effects of austenitizing procedures,deformation temperature,deformation rate,deformation amount and inter-pass time between deformations on the volume fraction of static recrystallization and the residual strain ratio of non-quenched steel C38N2 for crankshafts were carefully investigated by hot simulation tests,quantitative metallography and transmission electron microscopy. Experimental observations show that,the volume fraction of static recrystallization increases and the residual strain ratio decreases when the deformation temperature,deformation rate,deformation amount and inter-pass time between deformations rise. The situation is opposite when the austenite grain size increases,but they change inconspicuously. In addition,the volume fraction of static recrystallization decreases gently when the austenitizing temperature rises below 1250℃. However,it sharply decreases when the austenitizing temperature rises above 1250℃. A mathematical model of the relationship between the volume fraction of static recrystallization and deformation parameters was derived by linear fitting and least square method. Besides,a mathematical model of residual strain ratio concerning the deformation rate term was obtained by modifying the existent mathematical model,and it fits the experimental results better.
Abstract: The oxidation and carburizing mechanisms of Cr35Ni45 type pyrolysis furnace tubes serviced for different time(as-cast,1.5 a and 6 a) were systematically investigated by scanning electron microscopy(SEM),electron probe and X-ray diffraction(XRD).Compared with original uniform microstructure distribution,there are three zones including an oxidation layer,a carbide depletion zone and a carbide-rich zone at the subsurface region of the Cr35Ni45 tube inner wall after long time service. The oxidation behavior of the Cr35Ni45 tubes at high temperature consists of the external oxidation of chromium and the internal oxidation of silicon,and the outer oxidation layer is greatly affected by repeated destruction and reformation in decoking. The carburizing behavior of the Cr35Ni45 tubes mainly results from coking on the inner wall surface,and repeated destruction of the outer oxidation layer can aggravate this carburization. But due to auto-remediation of the outer oxidation layer,carburization of both the serviced tubes is at a lesser degree. Also,repeated destruction and reformation of the outer oxidation layer cause the depletion of Cr,the increase in critical concentration of C in the subsurface of the inner wall and carbide participation at the below region,leading to the formation of a carbide depletion zone and a carbide-rich zone.
Abstract: The effects of Mn,Cr and Ni on the solidification mode and nitrogen content of as-cast stainless steel were studied by smelting experiments. The key influencing factors on nitrogen content were explored. The coefficients of interaction between alloying elements and nitrogen were analyzed in molten steel and solidified steel. The results show that the nitrogen content is determined by both the solubility of nitrogen in molten steel and the solidification mode. When the solubility of nitrogen increases and the solidification mode changes according to the sequence of F→FA→AF→A,the solid solubility of nitrogen in the primary crystal enhances and the emission of nitrogen gas lessens during solidification. With the increase of Mn content,the nitrogen content increases monotonically.However,the nitrogen content varies with the Cr and Ni content in the above processes non-monotonically. The content of Mn does not change the solidification mode which is always FA,and the interaction coefficient is-0.0286,similar to that in molten steel; whereas the increase of Cr and Ni changes the solidification mode according to the routine of F→FA→AF→A and FA→AF→A,respectively,the interaction coefficients between alloying elements and nitrogen in the steel are not a fixed value,ENCr=-0.046 and-0.011,ENNi=-0.011 and 0.033,respectively.
Abstract: The cavitation erosion behavior of Cr32Ni7Mo3 N hyper duplex stainless steel in both distilled water and artificial seawater was investigated by a magnetostrictive-induced cavitation facility. The micrographs of damaged surfaces after cavitation for different intervals of time were observed by scanning electron microscopy(SEM). The cumulative mass loss curves and cumulative mass loss rate curves of specimens were drawn by measuring the weight loss. The polarization curves and free-corrosion potentials of specimens were measured by electrochemical workstation in the static state and in the cavitation erosion condition. A comparison of cavitation erosion resistance was performed between the material and SAF2205 steel in artificial seawater. The results show that cavitation damage firstly occurs in the ferrite weak areas and ferrite-austenite phase boundaries,then gradually expands to the ferrite phase,and the ferrite phase dissociates off at last. Its failure mode is cleavage brittle fracture. As the cavitation erosion time prolongs,the austenite phase microhardness value increases because of slip lines generating more. During the entire cavitation,the microhardness value of the austenite phase in artificial seawater is higher than that in distilled water. When the ferrite phase is largely destroyed,austenite phase damage begins to happen and drop off. Its failure mode is ductile failure. So the existence of austenite delays fracture expanding to the entire material surface. In artificial seawater,the interaction of both cavitation erosion and corrosion leads to material failure acceleration,and the cavitation erosion resistance of Cr32Ni7Mo3 N steel is better than that of SAF2205 steel.
Abstract: A sol-gel method was applied to prepare ZrO2 and Al2O3 coatings on stainless steel(SS304) substrates and to seal the anodic oxidation films of an aluminum alloy. The high-temperature oxidation resistance of as-prepared ZrO2 and Al2O3 coatings was investigated by cyclic high-temperature oxidation tests. The corrosion resistance of the sealed anodic films was investigated by electrochemical impedance spectroscopy(EIS) and exfoliation corrosion method. The experimental results indicate that the high-temperature oxidation resistance of the ZrO2 and Al2O3 coatings is improved with the increasing of coating thickness,and the corrosion resistance of the sealed anodic films is also improved with the increasing times of sealing processes. However,the impedance value and corrosion degree of the sealed anodic films change slightly after more than 8 times of sealing processes. The corrosion resistance of the anodic films sealed with Al2O3 sol performs a little better than those with ZrO2 sol with the same times of sealing processes.
Abstract: The effects of AC current density on the corrosion behavior of X65 steel in concentrated carbonate/bicarbonate solutions were studied by potentiodynamic polarization curve measurement,immersion testing and the surface characterization technique. When the AC current density increases,the passive region significantly narrows,the pitting potential negatively shifts,the passive current density increases,and the corrosion of X65 steel accelerates. At low AC current density(100 A·m-2) the passive current density,the pitting corrosion degree and the corrosion rate slightly increase with the increasing of AC current density,but at high AC current density(≥ 100 A·m-2),they increase rapidly.
Abstract: Hot-pressed boron carbide and aluminum foams were connected by epoxy resin to prepare bilayer composite materials.The ballistic resistance of the composite materials was investigated by ballistic testing using the materials as target plates. Armor piercing projectiles,7.62 and 12.7 mm in caliber,respectively,were used as test projectiles. The impact velocity was probably of the order of 820 m·s-1and the shooting distance was 10 m. It is found that the composite materials have good ballistic resistance to 7.62 mm-caliber armor piercing projectiles,with the protecting factor in the range of 5.06 to 5.12.
Abstract: A special die of precision forging was designed for gear shafts. Metal forming and flow in the forging process were studied by finite element method and forging trials. The cause of tooth filling defects in the precision forging was analyzed:filling of the tooth corner is one of the key influence factor of a sharp rise of forming load. The forging die cannot bear the high load of fully corner filling due to its special structure. Based on the analysis of corner filling,chamfered relief and annulus relief were proposed for the precision forging. Finite element method was used for simulating the two relief processes and the conventional precision forging of gear shafts. It is shown that the two relief processes can both reduce the resistance of metal flow into the tooth corner,ensure well filling of the tooth corner and low forming load. Moreover,chamfered relief is better than annulus relief in the precision forging. Forging trials proved the validity of finite element simulation.
Abstract: To cope with the high NOxemission problem of W-shaped radiant tubes,the influence of diluents in two-stage air combustion on the NOxemission of W-shaped radiant tubes was investigated numerically. Calculation results coincide well with data obtained from experiments. The analysis was carried out for 3 cases:different diluents,stepwise dilution,and diluents together with high temperature air. Compared to diluting with N2,diluting with CO2 produces less NOx. It can reduce the NOxemission blow 4 ×10-5 by increasing the diluted volume fraction under the condition of ensuring flame stabilization. By stepwise dilution,the secondary air contributes more to NOxreduction than the primary air. The NOxemission can be controlled under 1 × 10-4 by increasing the diluted volume fraction,even if the temperature of preheated air reaches above 1000℃.
Abstract: The effects of influencing factors such as gas flow rate,liquid flow rate,CO2 volume fraction,absorption temperature and their interactions on the percent conversion η and the volumetric overall mass transfer coefficient in gas phases KGaeby diethanolamine(DEA) aqueous solution were systematically studied by using orthogonal experimental design and statistical analysis. The impact significance of these influencing factors was estimated. It is found that gas flow rate,liquid flow rate,CO2 volume fraction,absorption temperature,the interactions between CO2 volume fraction and gas flow rate,between absorption temperature and liquid flow rate,and between absorption temperature and gas flow rate have remarkable effect on η; however,gas flow rate,liquid flow rate,CO2 volume fraction,absorption temperature,the interactions between gas flow rate and CO2 volume fraction and between gas flow rate and absorption temperature have distinguished influence on KGae. With the increment of gas flow rate,η decreases,while KGaeincreases.η and KGaeincrease as the liquid flow rate increases,but they decrease as the CO2 volume fraction increases. The impact of absorption temperature on η and KGaeis approximately parabolic.
Abstract: The hysteretic characteristic was introduced into the activation functions of neurons,and a forward hysteretic neural network was proposed. In combination with the Kalman filter algorithm,the hysteretic neural network was applied to wind speed forecasting. A change rate series of wind speed was constructed according to the original wind speed time series. Forecasting analysis of both the series was performed with the hysteretic neural network,these prediction results were fused using the Kalman filter algorithm,and thus the optimal estimated results were obtained. Simulation results show that the hysteretic neural network has more flexible structure,better generalization ability,and better prediction performance than the conventional neural network. The prediction performance can be further improved by Kalman filter fusion.
Abstract: Mining method selection was handled as a system engineering problem with multi-objective decision-making. First,a comprehensive multi-objective decision-making index system for mining method optimization was built in consideration of technical feasibility,economic benefit,resource utilization,labor productivity,safety and environment factors. Then,the analytic hierarchy process,fuzzy judgment matrix and Delphi method were used to get three groups of single weights for the decision-making index system.On this basis,a group of reasonable combination weights were determined through Kendall nonparametric test and Spearman rank correlation analysis. This provides a better solution for weight distribution in multi-objective decision-making,and can improve the rationality and scientificity of weight-determining methods for the decision-making index system. Finally,Jinshandian iron mine was taken as a case study on mining method selection,and the optimal mining method,sublevel open stope with backfill,was determined by this combination weight and fuzzy multi-objective decision-making method.
Abstract: This article focuses on the stability of networked control systems(NCSs) with variable sampling and time delay. NCSs are modeled as an equivalent input delay system. By introducing a novel Lyapunov functional with discontinuities,linear matrix inequality(LMI) based sufficient conditions are derived for the exponential stability of the closed-loop system. By solving these LMIs,we can find a positive constant that determines an upper bound between a sampling instant and the subsequent input update instant,which guarantees the stability of the closed-loop system. Numerical simulation examples show that this method is efficient and less conservative than existing results in the literature.
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
