Abstract: Central composite design (COD) experiments were performed to investigate the effect of stope temper-ature, cement-to-tailings mass ratio and the mass fraction of solid phases in the backfill slurry on the backfill strength characteristics and slurry flow properties for an alpine mine. Response surface regression models of backfill strength, slurry slump and the cost of filling materials were established by the substitution of a polynomial for the implicit limit state equation. Taking the desirability of the above regression models as inputs, the overall desirability of the back-fill slurry's performance was calculated by a weighted geometric average algorithm. The filling mix parameters were optimized by the method of nonlinear multi-objective based on the overall desirability criteria, and the optimal cement-to-railings mass ratio and slurry transportation concentration were obtained for the alpine mine in different temperature situations. It is found that at the stope temperature less than 5℃, the overall desirability of the backfill slurry is in the range from 0.4 to 0.5 when the mass fraction of solid phases in the backfill slurry is 70% and the cement-to-tailings mass ratio is 1:6. Under that condition, the backfill slurry meets the challenge of low temperature and the overall desirability primary keeps invariable with the change in temperature. But at the stope temperature higher than 5℃, the overall desirability improves significantly with the temperature increasing, and it raises fastest when the mass fraction of solid phases in the backfill slurry is 65% and the cement-to-tailings mass ratio is 1:6.
Compassion experiments of tailings were carried out with a self-made deep cone model, and the compaction effects were investigated under the conditions of dynamic compaction and static compaction. When the rotational speed is 0.05 to 0.80 r·min-1, the limit mass fraction of tailings is in the range of 67.41% to 70.73%; under the same conditions, it is only 55.82% for static compaction. Dynamic compaction has a higher compaction because excess water can move up through the water-guiding rod, but static compaction mainly relies on the gravity. The extrusion process of tailings can be simulated by theoretical extrusion models:the static compaction behavior corresponds to a simple spatial structure, while a cone structure for the dynamic compaction behavior. The theoretical value of unit sedimentation height calculated by the two kinds of models is 29.32%, and the test result is 28.81%, 0.51% lower than the theoretical value.
Abstract: This article reports the microscopic properties of polyurethane and expansive cement jelly composite material (PD composite material) as well as their impacts on the sealing performance of boreholes. Simulated experiment of the coal mine drilling sealing process was carried out, and FEI QuantaTM 250 environmental scanning electron microscopy was used for analyzing the microstructure of polyurethane and PD composite material, together with the combination, penetration and development of these two materials with the coal wall. It is found that the permeability coefficient of PD composite material is approximately 1/48 of that of polyurethane. Polyurethane has a cellular network structure and larger internal porosity, and there exists a blank area between polyurethane and the hole wall. However, PD composite material has a smaller internal porosity, and the tight structure makes the combination of PD composite material with the hole wall more compact. Compared with polyurethane, PD composite material is easier to overcome gas pressure and water resistance and then gradually infiltrate at the fracture zone around the borehole. Moreover, PD composite material can continue to develop in residual cracks and holes around the borehole.
Abstract: Intensive steel samples were taken from industrial beats at various time in a ladle furnace during BOF-LF-CSP process. The compositions, size distribution and change in number of inclusions in the samples were statistically analyzed by using an ASPEX scanning electron microscope. It is found that the number density and area fraction of inclusions in the samples sharply increase after Al addition. Then the number density has little changes while the area fraction obviously decreases during the period between 20 min-refining and soft blowing before Ca treatment. At the end of refining, the inclusions are mainly MgO-Al2O3 spinels containing little amounts of CaO. Both the number density and area fraction increase after Ca treatment, and the typical inclusions at this moment are calcium-aluminates and CaS due to excessive Ca treatment.
Abstract: An oxide dispersion strengthened (ODS) ferritic steel with the nominal composition of Fe-12.5Cr-2.5W-0.4Ti-0.02V-0.4Y203 (designated 12Cr-ODS,% by mass) was produced by powder metallurgy. Its microstructure and mechanical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical properties testing. Quantitative calculations were performed to find out the contribution of different strengthening mechanisms to the yield strength of the steel. SEM and TEM observations show that the steel exhibits equiaxed ferritic grains, its average size is 1.5 μm, and oxide particles of different sizes appear quite homogeneously distributed in the matrix. Tensile testing results indicate that the steel has superior tensile strength with the high yield strength of 738 MPa at room temperature. Orowan strengthening, work hardening effect of reinforced particles, dislocation strengthening by thermal expansion mismatch, and grain boundary strengthening are the main strengthening mechanisms of the steel. The theoretical yield strength is 750 MPa, which is in good agreement with the experimental data.
Abstract: Two kinds of 6 mm hot rolled plate steels, (0.22/0.17)C-(1.91/1.85)Mn-(1.32/0.94)Si, which have different precursor microstructures were heat treated by the critical region reheating, quenching and medium temperature isothermal processes (named T1 and T2). After the processes, a multiphase microstructure, which is composed of ferrite, bainite, martensite and well-distributed retained austenite (primarily distributed in prior austenitic grain boundaries and phase boundaries), was obtained for both of the steels, The microstructures of the steels in different heat treatment stages were characterized by scanning electron microscopy, X-ray diffraction and electron backscatter diffraction. It is found that making use of different precursor microstructures can well lead to the regulation of morphology, proportion and carbon content of the reversed austenite during the process of critical region reheating, and then achieve the regulation and control of the multiphase microstructure by the subsequent quenching and medium temperature isothermal processes. After the process of T1, 0.22C steel which has a martensite precursor microstructure can obtain a multiphase mierostructure with acicular-like ferrite as the matrix, and its product of strength and elongation is greater than 30 GPa.%. After the process of T2, 0.17C steel which has a ferrite + martensite precursor microstructure can obtain a multiphase microstructure with block-like ferrite as the matrix, and its product of strength and elongation is greater than 27 GPa.%.
Abstract: To study the thermal aging of the nuclear primary pipe material Z3CN20-09M, accelerated thermal aging experiments were performed at 300, 350 and 400℃ for 30000 h. Charpy impact energy and nanohardness of ferrite phase were tested for samples with different thermally aged time. Taking Charpy impact energy as the standard of thermal aging embrittlement, the thermal aging activation energy of the material was obtained to be 51.962 kJ·mol-1 by the fitting method. Meanwhile, the thermal aging parameter P was used to describe the kinetics of thermal aging embrittlement with Charpy impact energy. Finally, the Charpy impact energy and nanohardness of the material during 40 operation years at the actual operation temperature were estimated by the thermal aging activation energy and the thermal aging kinetics. The predicted results show that the toughness of the material decreases fast in the early 5 years, and then undergoes a slowly-decreased operation process.
Abstract: Tensile tests at different temperatures were performed on a Gleeble-1500 hot simulator to investigate the hot plasticity of the third generation of automobile steel (TG steel). The fracture morphology and fracture mechanism were analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). It is found that the strength of the steel decreases with temperature rise. The curve of hot plasticity consists of three segments:the first brittle zone, the high-temperature plastic zone and the third brittle zone. The curve in the third brittle zone contains two relative minimum points. In the temperature range of 800 to 1300℃, the microstructure of the steel is austenite, and the fracture mode is ductile fracture. Due to dynamic recrystallization, large plastic deformation occurs before the material breaks off, big and deep dimples form on the fracture surface of samples. At 750℃ there is a uneven distribution of ferrite along austenite grain boundaries, the fracture mode is interface fracture, and the fracture surface includes both holes caused by cohesive failure and the part like stones caused by crack enlargement along austenite grain boundaries. The plasticity of the steel at 650℃ deteriorates, and the quasi-cleavage of ferrite leads to a minimal value in the curve of hot plasticity again.
Abstract: The fracture of a 22Si2MnCrNi2MoA drilling rod near the internal thread was analyzed in term of the microstructure, inclusions and fractograph by means of optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Fatigue crack initiation and propagation in the drilling rod were studied. It is found that the fracture of the drilling rod is not induced by the abnormal microstructure and inclusions. Instead, because the wall thickness of the drilling rod near the internal thread is obviously uneven, the area with a thinner wall thickness tends to be the weak load-bearing point under the continuous stress of high frequency, serious outside consumption and internal friction existing simultaneously. Thus fatigue cracks are likely to emerge in the area preferentially. After that, the drilling rod ruptures in the area and eventually fractures. Furthermore, this fatigue failure is originated from the inside surface of the drilling rod and it belongs to the fatigue fracture with many crack sources. The morphology of the zones around the crack sources is dimple fracture, but the morphology of the zones of crack propagation is a mixed type with dimple and intergranular fracture.
Abstract: Nanocrystalline Ni coatings with (111), (200) and (220) textures were respectively pulse-electrodeposited on brass. Scanning electron microscopy (SEM) was used to observe their microstructures, X-ray diffraction (XRD) analy-sis was adopted to identify the texture degree, and the anodic polarization curves and electrochemical impedance spectra were tested to investigate the corrosion resistance of the pulse-electrodeposited Ni coatings in 3.5% NaCl solution. An obvious difference in corrosion resistance exists among the coatings with different textures. The coating with (220) texture exhibits the worst corrosion resistance, with the corrosion current density of about 1.23μA·cm-2 and the coating polarization resistance of 2.09 kΩ·cm2; the coating with (200) texture has the best corrosion resistance, with the corro-sion current density of about 0.15μA·cm-2 and the coating polarization resistance of about 27.32 kΩ·cm2; the coating with (111) texture shows a corrosion resistance in between. The difference of surface island microstructures incurred by growth textures might be the reason for the different corrosion resistances of the as-deposited Ni coatings.
Abstract: With the rapid development of high-speed rails, high-strength aluminum alloys are widely used in the lightweight design, but the service safety assessment of gear boxes in high-speed trains needs to be improved in China. An acoustic emission tensile test system was built for high-speed train gearbox shells made of aluminum alloys. After training and recognition by a BP neural network, acoustic emission signal was used for characterizing tensile damage in the materials and warning the materials service status. The research provides a method of nondestructive real-time characterization and warning for damage in aluminum alloys.
Abstract: In combination with a moving mesh technique and a level set function, the corrosion behavior of AZ31 magnesium alloy with a continuous β phase network and the discrete β phase around the a phase in a sodium chloride solution was investigated by finite element method. The distributions of potential and the concentrations of chloride ions and magnesium ions on the interface of magnesium/chloride solution during the corrosion progress were obtained by solving the Nernst-Planck function. The feasibility of this simulation method was validated with scanning ion-selective electrode experiments. Simulation results show that when the β phase is a discrete distribution around the a phase, the corrosion rate of the a phase adjacent to the β phase is the highest, a indented corrosion pit form at this place and chloride ions are enriched, which leads to the acceleration of the corrosion rate of the a phase. Finally, the β phase is removed from the alloy into the solution. However, when the β phase is a continuous distribution around the a phase, the solving process tends to be halted after the a phase is totally dissolved and only the continuous β phase is exposed to the chloride solution. Results of scanning ion-selective electrode experiments indicate that this simulation method can predict the electrochemical corrosion of magnesium alloys well.
Abstract: Rhodium nanoparticles (Rh NPs) were successfully fabricated on indium tin oxide (ITO) substrates through an electrochemical route. Capping agents, supporting electrolytes and electrochemical parameters were found to significantly affect the morphologies and sizes of the products in this process. Variously shaped Rh NPs including quasi-spherical nanoparticles, nano-islands and nanoplates were obtained by tuning the aforementioned parameters. Further research on the application of the Rh nanoislands-modified ITO in surface enhanced Raman scattering (SERS) indicates that it serves as an effective SERS substrate.
Abstract: TiO2-SiO2 composite aerogels with different contents of SiO2 were synthesized through a sol-gel route with tetrabutyl titanate and tetraethyl orthosilicate as the raw materials. In combination with solution aging and pinhole drying processes, monolithic TiO2-SiO2 composite aerogels were prepared via ambient drying, and their microstructure and the physicochemical properties were studied by scanning electron microscopy, BET method and X-ray diffraction analysis. It is found that the composite aerogels have low density, high specific surface area and show uniform element distribution of Ti and Si. With the increase of SiO2 content, the density of the composite aerogels decreases gradually, the specific surface area and the porosity increase, and the phase transition temperature to anatase rises. By calcination at high temperature, the composite aerogels change into anatase structure. The photocatalytic properties of the calcined samples were investigated by degradation experiments of the aqueous emulsion of crude oil from the Bohai Sea. The experimental results show that the photocatalytic degradation efficiency of the calcined sample increases with the mole fraction of SiO2 increasing till 30%, but it decreases when the mole fraction of SiO2 is above 30%. The best photocatalytic performance is acquired when the calcined sample contains 30% SiO2, with the catalytic degradation efficiency for 90 min being up to 95%.
Abstract: To solve the problems of environmental pollution caused by blast furnace slag and desulfurizationsintering flue gas (FGD) ash, a composite cementitious material was prepared using steel slag, sintering FGD ash and cement clinker. The results show that with the amount of sintering FGD ash increasing, the strength of the cementitious material increases firstly and then decreases. When the oxidation temperature of sintering FGD ash is 550℃, the oxidation time is 30 min and the added amount is 5%, the cementitious material achieves excellent reaction performance. The strength of the cementitious material can meet the requirement of 52.5R cement strength in Chinese IndustrialStandards GB 1344——1999.
Abstract: A three-dimensional simulation model was built to investigate the temperature field of the heating segment of a bright annealing muffle furnace. Based on the actual structure of the muffle furnace as well as the annealing speed and heating curves of steel strips, the equivalent heat flux was proposed in this model to characterize heat exchanges between the protection gas and steel strips in the muffle furnace. Then the combustion model for the transport and reaction of gaseous components, the radiation heat transfer model and the k-ε two-equation turbulence model for turbulent flow in the muffle furnace were adopted respectively. The SIMPLE method was used to solve the model. Simulation results by the model are consistent with the measured temperature values of characteristic points in an SUS304 stainless steel strip during the bright annealing process. The temperature, velocity and flow fields in the muffle furnace were obtained by this model. It is shown that the distribution of temperature on the muffle tube surface is relatively even, and only the zone of the burner has a higher temperature. The muffle tube is approximately uniformly heated since the combustion gases flow along the muffle tube spirally. With the injection quantity (inlet velocity) increasing, the temperature in the muffle furnace rises gradually; however, when the injection quantity is above a limit, the temperature in the muffle furnace begins to drop.
Abstract: A new spectral correlation density method based on kurtosis energy is proposed in this article. In the method the kurtosis of every slice along the cyclic frequency axis is calculated and used as the weight coefficient to evaluate the modulation ability of the corresponding cyclic frequency, and then the fault feature is effectively extracted by energy accumulation of the cyclic frequency. Compared with the traditional spectral correlation density (CSD) method, the proposed method has great performance of reduction the influence of multiple-frequency harmonics on the characteristic fault frequency, so the fault feature is extracted more clearly and accurately. Simulation signals and the fault signals from the outer ring of a rolling bearing in a low-speed and heavy-duty test bed have been analyzed by CSD, the proposed method and resonance demodulation. The analysis results prove that the proposed method is effective.
Abstract: A six-bar full-compliant mechanism was designed, and its pseudo-rigid-body model was established, which shows that it is composed of two compliant slide mechanisms. Deformation analysis of the full-compliant mechanism was performed according to the pseudo-rigid-body model, and a theoretical formula of force and displacement was deduced for the pseudo-rigid-body model. An example was presented to embody the full-compliant mechanism, and its relationship of force and displacement was numerically analyzed using ANSYS software. Meantime, a physical model of this example was manufactured for experimental measurement. By comparing the results of theoretical calculation, simulation analysis and actual measurement it can be concluded that the results of the three methods are basically the same, indicating that the theoretical derivation and analysis of the formula is correct, the simulation analysis is precise, and the design of the example is feasible to achieve the design goal.
Abstract: In order to make mutual coordination in the main process of steelmaking, continuous casting and hot rolling, improve the production plan level and enhance resource allocation benefits in steel enterprises, a unified model was applied to describe the rolling plan, charge plan and cast plan. Meantime, object functions during various plans were integrated from the perspective of universality to connect the production plan in each stage. The model was solved to make the integrated planning by a designed co-evolutionary algorithm based on a multi-agent system. Model test was performed in a steel enterprise according to its production plan, and the simulation results show that the model is effective.
Abstract: Based on studies on the existing three-dimensional (3D) ear reconstruction method and morphable model theory, considering the unique structure of human ears, a novel 3D ear reconstruction method was proposed, which is based on the 3D ear morphable model. First, ear feature points on the contour were located by the perpendicular bisector method. Then, the dense match of 3D ear samples based on physiological characteristics was realized by a hierarchical triangle mesh method. The generalized Procrustes analysis was performed, and the ear shape alignment was achieved accurately and automatically in the 3D space. Finally, the 3D ear morphable model was trained by using 3D ear data from the University of Notre Dame (UND) 3D ear dataset. This method can reconstruct the corresponding dense 3D model using only one 2D ear image. Extensive experimental results on UND collection J2 dataset and USTB ear image database for reconstruction show that the Drooosed method is effective and advantageous.
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
