Abstract: The grain body creep of waste dumps including deceleration creep and constant creep was described by the Burgers model.Using the layered summation method,the vertical filling waste dump was sliced and the bottom part settled under the variable weight load of the overlaid part.The computational formulas of settlement in the waste dump filling dynamic process,post-construction settlement and cumulative settlement were derived from theoretical analysis though the steady and unsteady Burgers creep models.The monitoring data of Qidashan Iron Mine were used as a case of proofing.The results show that the correlation coefficients of fitting with both the unsteady and steady Burgers models are high,and the final settlement value of the former is 5.07 m,while the settlement curve of the latter is divergent,thus the unsteady Burgers model performs better in simulating the real working condition of mine subsidence.The waste dump was divided into ten layers and the settle rate of each layer was calculated by the creep simulation model in Flac3D.The post-construction settlement of the top layers is smaller than that of the middle layers and bottom layers,the settlement of the top layers decreases when getting closed to the upper surface of the waste dump.The settlement of the middle layers is larger than that of the bottom layers,and the fifth layer performs a largest settlement.
Abstract: The inhibition mechanism of iron mineral reduction in laterite nickel ore with the addition of sodium sulfate was studied in the paper.It is found that sodium sulfate can change the reduction process of iron mineral,with FeS and aluminosilicates containing iron generated,and make the content of liquid phase in the roasted ore increase.The increase of liquid phase suppresses the coal gasification reaction,weakens the reducing atmosphere,and inhibits the diffusion of reducing gas at the same time,which is adverse to iron mineral reduction.FeS and aluminosilicates wrapping around FeO restrains the reduction of FeO,and aluminosilicates can react with FeO to generate more liquid phase in the inhibition process,leading to a further inhibition of FeO reduction.
Abstract: This article is focused on the leaching kinetic of copper oxide ore containing carbonate gangue.The effects of temperature,acid concentration,particle size,liquid-to-solid ratio and stirring rate on leaching of the copper oxide ore were determined.The results show that high temperature,high acid concentration,high liquid-to-solid ratio,low particle size and high stirring rate benefit the copper leaching.However,the carbonate gangue leads to a high consumption of acid.In consideration of leaching cost,the proper leaching condition is the temperature of 303 K,acid concentration of 35 g·L-1,particle size of 0.074-0.125 mm,liquid-to-solid ratio of 3:1,and stirring rate of 180 r·min-1.After leaching for 180 min,the copper leaching rate reaches 53.6%.The morphologies of the ore surface before and after leaching were investigated and the results reveal that the carbonate gangue dissolves in the acid solution and CaSO4·2H2O precipitation forms on the ore surface,which limits the development of porosity and cracks.Based on the shrinking core model,the leaching kinetic was analyzed.It is found that the precipitation on the ore surface hinders the leaching reaction.The diffusion across the product layer is the rate-controlling step and the activation energy is determined to be 8.65 kJ·mol-1.
Abstract: The characteristics of commercial pure aluminum and a super high strength aluminum alloy as cathodes in zinc electrodeposition were studied in this paper.In a ZnSO4-H2SO4 system,the electrochemical behavior of the two cathodes was investigated by electrochemical test,the initial nucleation was observed by scanning electron microscopy,and the crystalline orientations of zinc sheets were observed by X-ray energy dispersive spectrometry.The results show that under a current density of 500 A·m-2,the deposition potential and exchange current density of the commercial pure aluminum and super high strength aluminum alloy are -1.541 V,7.74×10-11 A·cm-2 and -1.496 V,6.07×10-3 A·cm-2,respectively.The addition of alloying elements can increase the initial nucleation sites and promote the rate of nucleation,but the increase of nucleation rate can inhibit cathode corrosion by halogen elements.There is no change in the crystalline orientations of zinc sheets after deposition for 3 h.The super high strength aluminum alloy is prone to burn the plate and blister,with a lower current efficiency of only 84.54%.The current efficiency of the pure aluminum is 88.04%,the morphology of deposited zinc is flat and smooth,but the cathode plate is easy to be corroded by halogen elements.
Abstract: Foaming slags at the top at the beginning of deslaggging, in the lower portion at the end of deslagging, and at the bottom after deslagging were taken with a sample scoop at the end of dephosphorization in the converter slag-remaining and double-slag process. The distribution characteristic of bubbles was analyzed by the macro & micro analysis technique. The results indicate that the order of average equivalent diameter of bubbles is the slag at the top > slag in the lower > slag at the bottom, and the order of gas porosity is the slag at the top > slag in the lower > slag at the bottom. The formation process of foaming slags was observed and analyzed. Bubbles collide and coalesce with CO/CO2 moving into the slag. Bubbles in the upper are elevated by bubbles in the lower and the bubbles rises up with buoyancy. The drainage of liquid slag occurs with gravity and the topological structure of bubbles changes. With bubble collision and coalescence, the foaming slag with larger bubbles and higher porosity in the upper and that with smaller bubbles and lower porosity in the lower are formed.
Abstract: To investigate the generation mechanism of oversized DS-type inclusions in low oxygen special steel,a comparative analysis of inclusions was performed on overseas and domestic special steel samples by the automatic secondary electron microscopy ASPEX PSEM explorer.Both the average size and maximum size of inclusions are larger in domestic samples than overseas samples.Particularly,the maximum size of inclusions in domestic samples is several times that in overseas steel samples:24.9 and 13.1 μm in domestic samples and 7.6 and 7.5 μm in overseas samples,respectively.Based on the chemical composition analysis of inclusions in domestic samples,it is found that the oversized inclusions and smaller inclusions have similar compositions.Therefore,the detected DS-type inclusions are endogenous but not exogenous,which can be produced by collisions among inclusion particles.To further study the possible origins of the oversized DS-type inclusions,in-situ observation on the behaviors of inclusions at the solid/liquid interface in low oxygen special steel show that tiny inclusions less than 5 μm can be easily and stably captured by the solid/liquid interface with a total oxygen content of 7×10-6.Moreover,collisions,agglomeration/coalescence and growth of inclusions captured by the solid/liquid interface result in the formation of much larger size DS-type inclusions over >12 μm.
Abstract: M2 steel was melted by a 25 kg high-frequency vacuum induction furnace and was cast to ingots with a cross section of 100 mm×50 mm by the water-cooled copper mould and the sand mould.The effects of cooling rate on the ingot's secondary dendrite arm spacing(λ2),permeability,and size and distribution of grains and carbides were studied.The results show that fast cooling rate can effectively decrease the λ2,permeability and size of grains and network carbides,and improve the distribution and uniformity of network carbides and grains during solidification.The λ2 values of ingots cast with the sand mould and the water-cooled copper mould are 42.5 μm and 21.6 μm,the cooling rate is 1.06 K·s-1 and 12.5 K·s-1,and the permeability is 1.3×10-1 μm2 and 3.5×10-2 μm2,respectively.Fast cooling rate can effectively reduce the center carbon segregation degree.The area fraction of carbides is 0.46 and 0.30 respectively at the center of ingots cast with the sand mould and the water-cooled copper mould,and increases by 38.7%and 2.2% respectively compared with their average values.The average grain size of ingots cast with the water-cooled copper mould and the sand mould is 41.3 μm and 72.6 μm,respectively.Comparing with the sand mould ingot,the grain size at the center of the water-cooled copper mould ingot reduces by 43.2%,and the grain size of the water-cooled copper ingot is more uniform.The relationship between grain size and cooling rate was presented in this paper.
Abstract: The static tensile behaviors of Fe-22Mn-0.7C TWIP steel and Q235 steel between 700 ℃ and 1300 ℃ were investigated by Gleeble-1500 thermo-mechanical simulator.The microstructure characteristic and fracture morphology were observed by optical microscopy,scanning electron microscopy,energy dispersive spectrometry and electron probe micro-analysis.The hot ductility and influenced mechanism were revealed based on the discussion of chemical composition,matrix phase volume fraction,grain size and solidification defects.It is found that the TWIP steel has a reduction in area lower than 40% in the temperature range of 700 ℃ to 1250 ℃,but its tensile strength is higher than that of Q235 steel.Fractographic results manifest intergranular fracture for the TWIP steel.Grain refinement and microsegregation descending in the TWIP steel are beneficial to increasing the hot ductility due to the improvement of matrix homogeneity.Besides,the tensile strength and reduction in area of the TWIP steel increase with increasing strain rate.
Abstract: The hot ductility of a Ti-bearing microalloyed steel was studied at temperatures of 600 to 1350 ℃ by a thermal simulator Gleeble 1500.The fracture morphology and microstructure were observed by scanning electron microscopy and optical microscopy.The precipitate behavior of second phase particles was calculated by the thermodynamic software Factsage.The hot ductility curve shows that SS400 B steel with additional titanium has very good hot ductility during all the tested temperature range,and all the values of reduction in area are larger than 45%.AlxTiyOz generation at high temperature can act as nucleation sites for dimples to promote the ductile fracture.The amount of detrimental Al N can be reduced due to the formation of AlxTiyOz and Ti N.Intergranular ferrite and cementite promote the intergranular brittle fracture.
Abstract: The unique texture evolution and secondary recrystallization behavior of medium temperature reheated grain oriented silicon steel containing copper were analyzed by comparison with those of conventional grain oriented silicon steel and high permeability silicon steel.The results show that to obtain a stronger γ-fiber primary recrystallization texture,which can be easily consumed by Goss grains,recovery annealing and slow heating rate of high temperature annealing are necessary.During the high temperature annealing stage,the strong γ-fiber primary recrystallization texture shows the effects of decreasing the stored energy caused by recovery annealing and increasing the nucleation rate of γ-fiber grains with slow heating rate.The onset temperature of secondary recrystallization exceeding 1000 ℃ and the strong γ-fiber primary recrystallization texture with less non-γ-fiber oriented grains indicate that the secondary recrystallization behavior is dominated by preferred grain growth.As a result,very huge secondary recrystallization grains with smooth boundaries are obtained.The iron loss is increased due to huge secondary grain size characterized in medium temperature reheated grain oriented silicon steel final products,but can be reduced significantly by magnetic domain refinement using laser scribing,compared with that of high permeability grain oriented silicon steel with small secondary grain size.
Abstract: To overcome the challenge of traditional roll forming process and equipment on high strength square tubes at room temperature,hot roll forming process using local induction heating was proposed to produce high strength square tubes.A series of tests including tensile testing,fracture morphology,scanning electron microscopy(SEM) and X-ray diffraction were performed to investigate the effect of hot forming temperature on the microstructure and mechanical properties of high strength square tubes.Experimental results show that as the temperature rises,the mechanical properties of the corners improve significantly.The fracture morphology gradually changes from cleavage fracture at room temperature to ductile fracture.The microstructures at the corners are developed from lath bainite to granular bainite and the polygonal ferrite begins to grow.Moreover,the circumferential and longitudinal residual stresses on the outside surface of the square tubes are reduced and reasonably redistributed.Based on the analyses of experimental results,the optimum forming temperature for high strength square tubes is 650 ℃.
Abstract: A hardness tester was used to make indentations on the hourglass fatigue specimens of axle steel,and notches were machined by electronic discharge machining(EDM).The fatigue limits of both indentation specimens and notched ones were examined and compared with the theoretical values according to the Murakami formula based on material hardness and defect projected area.The fracture surface was observed by scanning electron microscopy.It is found that local work hardening and residual stress caused by plastic deformation of indentations have no significant effect on the fatigue limits in comparison with the predicted values by the Murakami equation.Fatigue cracks originate from the bottom of indentations due to stress concentration effect.The fatigue limits of notched specimens are lower than the calculated values because of secondary notches caused by the high roughness of notch surfaces and the existence of microcracks and micropores within the re-cast layers.Cracks initiate from multiple sites on the bottom of electronic discharge machining notches.
Abstract: By using coal fly ash as a raw material and graphite as a reducer in the protective atmosphere of argon,SiC/Al2O3 composite materials were synthesized by carbothermal reduction.The reaction process of reduction of the coal fly ash was studied,and its influencing factors were investigated.The composition of products obtained at different temperatures was analyzed by X-ray diffraction,and the microstructure was observed by scanning electron microscopy and energy dispersive spectroscopy.The results show that the phases of quartz and mullite in the coal fly ash are almost completely reactive at 1673 and 1773 K,respectively.With increasing temperature,the contents of SiC and Al2O3 increase,and the suitable temperature condition is 1773 to 1873 K.The extension of holding time is good for the formation of SiC and Al2O3,and the appropriate holding time is 3 to 4 h.Increasing the carbon content has positive effect on the formation of SiC and Al2O3,and the optimum molar ratio of C/Si is 4 to 5.In the prepared SiC/Al2O3 composite materials,SiC is homogeneously dispersed in the products,and its granularity is less than 20 μm.
Abstract: This article introduces a new mortar fracture analysis method based on the phase-field method,which is used to analyze the fracture failure in crack interaction of mortar.The non-conserved Allen-Cahn equation was adopted as the system governing equation to study the crack development and interaction in mortar.Both the linear elasticity and phase-field equations were solved in a unified finite element frame work,which was implemented in the commercial software COMSOL.Direct tension test and three-point bending test were performed for validation.It is discovered that the critical load of crack interaction by the phase-field method agrees very well with the experimental results.Research results show that Mode Ⅱ specimen tends to have a longer crack path.
Abstract: To accurately capture micro frictional contact characteristics and intermolecular forces between tires and pavement,the three-dimensional monomer models and the interface contact model of tires represented by isoprene and aggregates represented by silica were established by the molecular dynamics method.The microscopic structure and tire-aggregate contact properties were studied in nanoscale.Simulation results show that polyisoprene molecular chain is in the spiral structure with big molecular gaps,and is easy to generate large deformation under external loading.Conversely,silica is brittle with relatively flat surfaces.In the tie-pavement contact model,silica is the fixed base,and the single-chain polyisoprene is sliding on the top of the silica base at a constant velocity.The surface distance between the silica base and the single-chain polyisoprene is 0.5 nm.Simulation results of tire-pavement contact show that the friction coefficient decreases with the increase of sliding velocity,and the relationship between the friction coefficient and sliding velocity shows good agreement with test results,indicating that molecular dynamics simulation is capable to predict the tirepavement frictional contact characteristics.
Abstract: To get the adsorption data of low-volatile organic compounds,a method for estimating the adsorption isotherm of low concentration and low-volatile organics was proposed based on the Langmuir equation.The desorption activation energy was calculated by a modified temperature program desorption(TPD) model,which is much closer to the intrinsic value,and then the Langmuir equilibrium constant B was obtained.In combination with sorbent characterization results,it was easy to estimate the saturated adsorption capacity.The adsorption isotherm of low concentration naphthalene on SBA-15 was estimated.The desorption activation energy,balance constant,and saturated adsorption capacity are 58.37 kJ·mol-1,0.01149 Pa-1 and 55.11 mg·g-1,respectively.The calculated values are in good agreement with experimental results,and the relative error is about 5%.
Abstract: Aiming at the problem of mismatch between the model and the process for a byproduct coal-gas system in a combined cycle power plant(CCPP) due to frequent changes in working conditions,this article introduces a method for online performance prediction of the CCPP byproduct coal-gas system based on an online sequential extreme learning machine(OS-ELM).Firstly,by analyzing the working principle of each main component in the byproduct coal-gas system and using the fluid mechanics,energy conservation and mass conservation principles,a mechanistic model is established for performance prediction of the byproduct coal-gas system,which essentially consists of scrubbers,centrifugal compressors,and coolers.Further,the OS-ELM and the sliding window technique are also used to correct the error of the mechanistic model,thus we realize the accurate prediction of export parameters and the update of the model in time.Simulation results show that this method can accurately predict the pressure ratio and temperature ratio of the byproduct coal-gas system and track the change in coal-gas system working conditions and the characteristics drift,which meet the needs of actual industrial production.
Abstract: This article is focused on a double-arm and double-manipulator live working robot.The arm motion of the robot for insulator string replacement during the operation process was decomposed.The basic operation dynamic model was established by the Lagrange method combined with the armature voltage equation,the dynamic equations of manipulator 2 were calculated,the manipulator motion trajectory planning method was proposed based on five-polynomial interpolation,and the kinematics equations of manipulator2 each joint were calculated.Robot manipulator dynamics and kinematics simulations were performed in ADAMS environment.The results verify the correctness of the dynamic model,and the joint trajectory planning meets the kinematic requirements.Finally,insulator string replacement experiments of the robot were tested on actual line.The results show that each robot manipulator joint movement obtains a better dynamic performance,which validates that the proposed five-polynomial interpolation manipulator trajectory planning has strong practicability,and can further improve the robot operational efficiency and stability.
Abstract: Specific to the problem of infrared target extraction with blurred edges,this article introduces an extraction method based on a manifold regularized multiple kernel semi-supervised classification model.Firstly,the maximum variance of inter-class(OTSU) method is used to compute the initial segmentation threshold,and the certain target and background areas and the uncertain blurred edge area are determined.Then,local space sets of pixels are constructed in each area,the multiple-kernel functions are used to map the grayscale mean and variance in local space,and the location information feature in local space is obtained by manifold regularization(MR).On the basis of features,a semi-supervised classification model is established to classify the local space sets of pixels in the blurred edge area.Finally,the optimal segmentation threshold is computed.Experiments with comparisons show that this method is efficient and less in time-consuming.
Abstract: To solve the problem of the low efficiency and accuracy of numerical data mining based on the Apriori categorization association rule algorithm,this article introduces a categorization and regression algorithm based on the quantitative association rule tree.The modified quantitative association rule algorithm is adopted to mine numerical datasets to generate an association rule base,and the association rule tree(QART) is reconstructed to realize the categorization and regression prediction.The results show that quantitative association based on the modified Apriori algorithm is helpful for improving the accuracy of categorization and regression and reducing the computational complexity,and the quantitative association rule tree can improve the efficiency of categorization and regression and increase the rule matching speed.
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
