Abstract: The dynamic response of underground caverns under open blasting loads was simulated with FLAC3D software.On the basis of data from seismic waves measured with an IDTS3850 tester,blasting vibration parameters in the case of the maximal charge amount of explosives and the shortest blasting distance were calculated with Sadowsky's empirical formula.By conversion of the velocity-time history into the stress-time history and by use of the Fish function built-in FLAC3D software,dynamic loading was carried out by inputting the dynamic load-time history at boundary nodes or internal nodes.After comparison between the dynamic simulation and static analysis of plastic zones,displacement and stress,the corresponding impact of dynamic loads on the stability of caverns was assessed.It is shown that blasting vibrations can magnify the vertical displacement of caverns,especially in intersect zones,and on the other hand,the stress concentration under static action is alleviated when a dynamic load is applied.Besides,it also aggravates the wall fall of cavities,but cannot result in overall destruction.
Abstract: The properties and morphological structures of three types of coal rocks were experimentally analyzed with MTS815.03 servo-control rock mechanical test system and S250Mk3 scanning electronic microscope.The micro and meso-damage mechanisms of the coal's strength and deformation characteristics were studied with using the theory of damage mechanics.It is shown that the micro and meso-damage variable has great influence on the coal's macroscopic mechanical parameters.The original damage variables of No.3 coal seam in Baodian Colliery and No.3 coal seam in Xuchang Colliery,which both belong to carboniferous-permian Yanzhou Coalfield,decrease by 68.5% and 50.6% compared with No.3 coal seam in Xinhe Colliery,the uniaxial compressive strengths increase by 224.8% and 109.9%,and the elastic moduli increase by 147.3% and 66.9%,respectively.With decreasing damage variable,the uniaxial compression failure gradually changes from plastic to brittle.Macroscopic mechanical properties of the coal rocks are closely related to micro and meso-damage.
Abstract: Full stress-strain tests and acoustic emission measurements under uniaxial compression,triaxial compression and pore water pressure were carried out on coal samples with an MTS815.02 rock mechanics test system.It is shown that the triaxial strength and residual strength increase with the increase of confining pressure but reduce with the increase of pore water pressure.In the testing range of low confining pressure,the elastic modulus has great change with confining pressure.Under different testing conditions,the acoustic emission behaviors of coal samples have great differences.Under uniaxial compression test,there are all acoustic emission events at each stage,but under triaxial compression and pore water pressure,the acoustic emission events are smaller before yielding and tend to be active after yielding.The acoustic emission energy of coal samples under uniaxial compression is the largest.With the increase of pore water pressure,the released acoustic emission energy decreases step by step in the process of deformation.
Abstract: Experiments on acoustic emission characteristics of rock and concrete samples were carried out with a servo-hydraulic test system and a smart acoustic monitoring device.Based on these experiments,the relationship between damage variable and acoustic emission(AE) parameter was investigated,and the results showed a linear correlation between them.By using the damage constitutive model based on Weibull distribution and the empirical relationship of damage variable versus acoustic emission number,the coupling models of acoustic emission parameter versus stress and strain were formulated.Parameters in the models can be determined according to the geometric boundary conditions of the full stress-strain curve and the curve of damage variable versus acoustic emission number.The process for acquiring these model parameters is simple and easy to use.A comparison between the results of the coupling models and the measured data by uniaxial compression testing for rock samples and concrete samples proves that the coupling models can better reflect the relations of acoustic emission parameter versus stress and strain.
Abstract: Based on the nonlinear thermo-elastic theory,a constitutive equation with variable properties was established in consideration of the expansion force of pore ice,and the relationships of the uniaxial compressive strength and the mechanical parameters with temperature were proposed in the drying and low-temperature condition and the saturated freezing condition.Mechanical properties of granite under uniaxial compression were discussed according to compression experimental results of granite in both the conditions.It is shown that the compressive strength under the saturated freezing condition is greater than that under the condition of drying and low temperature,and their difference increases with decreasing temperature.The compressive strength in the same state increases with decreasing temperature,and the growth rate gradually decreases.The additional strength is mainly caused by thermal effects of the rock matrix,and the expansion force of pore ice has relatively little effect.The elastic modulus of granite increases with decreasing temperature in both the conditions,but the change of Poisson's ratio is little.
A rotor was added to the experimental apparatus,making the apparatus more similar to an in-situ high-capacity thickener.With solid handling capacity per unit area and underflow volume concentration as two evaluating indicators of tailings thickening effect,the influence of some factors on tailings thickening effect was investigated using a uniform design method.It is shown that there is a positive correlation between the solid handling capacity per unit area and the flocculant's dosage,and the best feed volume concentration is 6.56%.The underflow volume concentration is of positive correlation with feed volume concentration,residence time and the flocculant's dosage,respectively.Through analyzing the settlement curve with a Cage settlement model,it is concluded that the speed limit layer is typically the separate layer of the transition region and the compression region.Based on experimental results and tailings handling capacity daily,the minimum diameter of a thickener is 14 m.
Abstract: In order to clarify the function of quartz in chalcopyrite bioleaching,quartz with particle sizes less than 43 μm was used to prepare a slurry system with chalcopyrite and pyrite for studying the effect of the mass concentration of quartz on the bioleaching efficiency of chalcopyrite.It is shown that the bioleaching of chalcopyrite can be improved by the addition of proper amount of quartz with finer particle sizes.Under the addition of 50 g·L-1 quartz whose particle size was less than 43 μm,the largest leaching rate of chalcopyrite is 54.09%.Based on the analysis of oxidation-reduction potential,pH values,Fe2+ and Fe3+ mass concentrations and the results of scanning electron microscopy and energy dispersive spectroscopy,quartz benefits the bioleaching of chalcopyrite,and this phenomenon mainly presents a decrease of bioleaching delay time.Moreover,new precipitates generated in the leaching process can be adsorbed by quartz,which reduces the hindrance of precipitation during chalcopyrite bioleaching.
Abstract: The treatment of Gacun complex silver copper concentrate with high Pb,Zn,Ag and Sb by a fluidized roasting synthetic reclaiming process was studied.The process consists of desulfurization by roasting,two-stage countercurrent leaching of copper and zinc with sulfuric acid,leaching of antimony and silver with chloride,leaching of gold with sodium chlorate,and transformation of lead with ammonia bicarbonate,and it can reclaim synthetically valuable elements well.Agglomerating of the concentrate can be avoided through controlling air surplus coefficient to be only 1.1,linear velocity in the hearth to be 0.25 to 0.35 m·s-1 and roasting temperature to be 600 to 630℃.The desulfurization ratio was 49.68% and the concentration of SO2 in smoke reached 5.5%,which meet the requirement of producing sulfuric acid in commercial production at these operating parameters.
Abstract: Changes in temperature of vanadium-titanium magnetite sintering feed at different depths during mineralization processes were studied by measuring the temperature values of different sintering layers.Two quantitative parameters,flame front speed and mineralization front speed,were defined to evaluate the inhomogeneous degree of vertical sintering.The results show that the flame front speed and mineralization front speed decrease with increasing layer depth,indicating that there is a serious structural change in the lower region of the sintering feed bed and the sintering permeability deteriorates.Promoting the charge segregation and increasing the mean diameter and thermal intensity of quasi-particles in the lower region of the sintering feed bed are of great importance for enhancing the sinter productivity.Simultaneously,mineralogical analysis of sinters at different sintering layers show that the vanadium-titanium magnetite sinter ore consists of magnetite,hematite,calcium ferrite,dicalcium silicate,perovskite,and vitreous mineral.With the layer depth increasing,the contents of magnetite,dicalcium silicate and perovskite increase,while the contents of hematite and calcium ferrite decrease.
Abstract: According to the Maxwell electromagnetic field theory,electromagnetic fields during mold electromagnetic stirring for 240 mm×280 mm bloom casting were simulated by means of ANSYS software.The distributions of magnetic fields and electromagnetic force as well as the effects of string parameters on magnetic field characteristics were analyzed.It is shown that the rotary magnetic field generates electromagnetic force in the mold region,which made molten steel whirl at the horizontal section.The characteristic of the magnetic field along the mold vertical direction was large in the middle and small at the end of the mold.The simulation results of magnetic induction density were consistent with the measured ones.Final,the optimized M-EMS parameters of the current intensity of 350 A and the frequency of 3 Hz for 45# steel blooms were proposed and the results indicates that the quality improves obviously.
Abstract: After gas nitriding three layers are formed on the surface of medium carbon railway axle steel from the exterior to interior,they are oxide layer,nitride layer and N-diffusion layer respectively.The effect of the three surface layers on the rotary bending fatigue properties of the steel was investigated in a very high cycle regime.Compared with the fatigue strength of untreated specimens,the strengths of nitrided specimens with the oxide layer,the specimens from which the oxide layer was removed and the specimens from which the nitride layer was removed greatly increased step by step.Nitrided specimens without the oxide layer fractured from the position between the compound layer and diffusion layer at the subsurface;while the ones without both the oxide and nitride layers fractured from the matrix.Through fractography and fracture analysis,the effect of the three surface layers on the fatigue properties was clarified in a very high cycle regime.
Abstract: The morphology,distribution and components of precipitates in Q960 steel under the conditions of the same composition,rolling technology and quenching process but different tempering temperatures were systematically investigated by using transmission electron microscopy(TEM),energy dispersive X-ray spectrometry(EDX) and a multi-function internal friction device.A law was proposed for describing the effect of tempering temperature on the structure characteristics of the precipitates.It was shown that the decrease of carbon solution content in martensite was greater when the tempering temperature was less than 400℃,but it was very slow when the tempering temperature was higher than 400℃.In addition,a large number of small parallel θ-carbides dissolved and were finally replaced by Cr carbides which precipitated along martensite lath boundaries.With the tempering temperature increasing,Nb,V and Ti composite carbon and nitrogen compounds grew up and their shape evolved from a square to an oval.
Abstract: The thermal expansion coefficient,high-temperature yield strength and Young's modulus of hot-rolled X70 pipeline strips were tested with a thermal expansion instrument and a thermal simulation test machine Gleeble3500.The temperature field,bainitic volume fraction and residual stresses in the hot-rolled strips during laminar cooling were calculated with the finite element software Marc when the coiling temperature is 500,550 and 600℃,respectively.It is shown that stresses in the strip edge exceed the yield strength of the steel at the same temperature in the earlier water cooling stage,leading to edge waves;but in the end of water cooling,stresses in the strip edge exceed the yield strength again and generates plastic deformation,which causes center waves.Reducing the coiling temperature is in favor of completing bainite transformation and decreasing residual stresses in the hot rolled strips on the assumption that the properties of X70 pipeline steel are ensured.
Abstract: Corrosion behaviors of steel in simulated concrete pore solutions with different pH values were investigated by means of a galvanostatic pulse method(GPM).The polarization resistance of steel was derived from time constant and double layer capacitance in GPM.The time constant value of passive steel is higher than that of active steel,while the double layer capacitance of passive steel is relatively lower than that of active steel.The better anti-corrosion capacity in the final corrosion period confirms that the steel exposed to CP solution(pH 13.6) has a better passive film than that exposed to CH solution(pH 12.5),but there is not any passive film on the steel exposed to CN solution(pH 11.0).The addition of SO42- and SiO32- into CP solution increases the polarization resistance,promoting the passivation of steel,especially in the corrosion period.Finally,the polarization resistance values measured by GPM were compared with the results of linear polarisation resistance(LPR) and electrochemical impedance spectroscopy(EIS).It is found that the correlation is acceptable for these electrochemical methods in evaluating the corrosion rate of steel in simulated concrete pore solutions.
Abstract: Fatigue crack propagation laws of aluminum alloys under Ⅰ-Ⅲ combined loading were investigated by finite element simulation and fatigue crack growth experiment,and the stress intensity factors under various loading conditions,the energy field around the crack front and the radius of the plastic zone were obtained.The effects of mode Ⅲ loading on the energy field around the crack front and the stress intensity factor under mode Ⅰ loading were analyzed on the basis of studies on mode Ⅰ loading.Numerical results show that under the condition of Ⅰ-Ⅲ combined loading,the stress intensity factor decreases with the increasing of mode Ⅲ loading,but the radius of the plastic zone near the crack increases.Mode Ⅲ static loading can slow down fatigue crack propagation,and to some extent,the fatigue crack growth rate under combined Ⅰ-Ⅲ loading decreases with the increasing of mode Ⅲ static loading.Mode Ⅲ cyclic loading can speed up fatigue crack propagation,and to some extent,the fatigue crack growth rate under Ⅰ-Ⅲ combined loading increases with the increasing of mode Ⅲ loading.
Abstract: Metal-particle-dispersed piezoceramics are a new type of 3-0 piezoelectric composite.The volume fraction of metal particles has large effect on the piezoelectric properties of the composite.In combination with that metal particle dispersion can result in a change in orientation distribution of the electric domain in piezoceramics,the influence of the volume fraction of metal particles on the piezoelectric properties of the composite was calculated according to the effective medium theory based on Green's function.It is shown that the effective piezoelectric properties of the composite decline with the volume fraction of metal particles increasing.The theoretical calculations are basically consistent with reported experimental results,indicating that this method enables us to accurately forecast the relationship between the structure and properties of the piezoceramics/metal composite.
Abstract: The light aging performance of nano-SiO2 particle composited polyurea coatings were tested by ultraviolet accelerated aging and surface morphology observations.The corrosion resistance to seawater of the coatings was measured by soaking in a 3.5% NaCl solution.Field emission scanning electron microscopy,corrosion potential measurements and electrochemical impedance spectroscopy(EIS) were used to analyze the corrosion resistance of different coatings.The results indicate that the corrosion resistance of aromatic polyurea coatings increases significantly by compositing the nano-SiO2 powder.After the compositing,the corrosion potential improves from-40 mV to 60 mV,the EIS modulus increases approximately one magnitude,the accelerated aging stage delays about 120 h,and the life of the coatings in the 3.5% NaCl solution increases by 600 h roughly.
Abstract: Fe3O4 magnetic nanoparticles were prepared by means of ultrasonic emulsification and then the Fe3O4 magnetic fluid was made by dispersing these particles into water with chitosan as surfactants.The influences of the molar ratio of Fe2+ to Fe3+,ultrasonic time and the amount of chitosan on the magnetic properties of the magnetic fluid were investigated.The results show that ideal Fe3O4 magnetic nanoparticles can be obtained under the condition that the molar ratio of Fe2+ to Fe3+ is 1:1.5 and the reaction temperature is 70℃ when dropping ammonia.The prepared magnetic fluid has high specific saturation magnetization and stability when the volume of the 1% chitosan solution is 50% as large as the total volume of the mixed Fe3O4 solution and the ultrasonic time after dropping chitosan is 7.5 min,which are in favor of coating the magnetic particles with chitosan.
Abstract: The effects of substrate pretreatments,such as modifying the substrate with ZnO nanoparticles,drying the substrate with highly pure nitrogen and soaking the substrate with hydrochloric acid,on the growth of ZnO micro/nanotube arrays were systematically investigated by using a hydrothermal method.The relationship between substrate surface characteristics and the growth of ZnO micro/nanotube arrays was discussed based on ZnO microstructure.It is indicated that ZnO micro/nanotube arrays with different sizes,morphologies and distributions can be obtained on indium-tin oxide(ITO) substrates pretreated by highly pure nitrogen and hydrochloric acid,respectively.The growth mechanism of ZnO micro/nanotubes showed that the Zn-atom surface termination of ZnO played the key role for formation of the micro/nanotubes.
Abstract: The forming process of light area reduction shafts by cross wedge rolling was simulated with the analysis software ANSYS/LS-DYNA.Surface and central qualities of light area reduction rolled pieces were analyzed in comparison with those of conventional area reduction rolled pieces.It is found that the ovality of the light area reduction rolled piece exceeds that of the conventional area reduction rolled piece under the same process parameter condition.Compared with the conventional area reduction rolled piece,the light area reduction rolled piece is more prone to central defects due to its both larger mean stress and maximum principal stress at the central point.Some measures to improve surface and central qualities of the rolled piece were proposed.Rolling experiments were carried out and the results demonstrate that forming light area reduction shafts by cross wedge rolling is feasible.
Abstract: The concept of safety factor with two-indexes of reliability and confidence levels was presented by introducing the confidence level index.Based on the reliability theory,new formulae of safety factor with two-indexes of reliability and confidence levels were derived to take the sample size of experimental data into account and to determine the safety factor value from small sample test data for structural reliability design.The new safety factor was applied to two sets of experimental results,demonstrating the practical and convenient use of the proposed technique.It is shown from these examples that the safe factor can be obtained realistically according to small sample test data using the new formulae.
Abstract: The effects of gas components such as O2,SO2 and HCl,the existence of fly ash,and temperature on mercury speciation were investigated.It is shown that high temperature is positive to mercury oxidation in most of the simulated flue gas system except for the N2-SO2 system.The existence of O2,SO2 and HCl in the system separately improves the oxidation process,and among them HCl performs the best.When both SO2 and HCl are in the system,the oxidation efficiency of HCl decreases due to the reaction between SO2 and HCl.Fly ash provides,reaction media and catalysts for the mercury oxidation reaction,and consequently,the existence of fly ash in the simulated flue gas can increase mercury speciation.
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
