Abstract: The models of rock mass with different joint states were established by using particle flow code (PFC) numerical simulation procedures, and then their biaxial test was simulated. The effects of intermittent joints on the rupture forms and mechanical properties of rock mass were numerically analyzed from three aspects of rock bridge length, joint length, and dip angle. The failure mode of rock bridges is mainly tensile-shear failure because of the extension of wing cracks, but the failure mode of the models can be concluded to be the extension of wing cracks and secondary cracks and the failure of rock bridges, exhibiting obvious creep properties and ductile failure. The peak strength and elastic modulus are less influenced by the change in length of rock bridges; however, compared to the length of rock bridges, the mechanical properties of the jointed rock samples are more sensitive to the length of intermittent joints. As far as models with the different dip angles of intermittent joints are concerned, the initial rupture forms of the models are different, the failure mode of the model with the dip angle of 0° is the extension of wing cracks and secondary cracks, but the middle rock bridge has not been run through, and the initial crack strength and peak strength of the model with the dip angle of 15° is maximum.
Abstract: To obtain brittle shear character parameters, acoustic emission accompanied with triaxial stress-strain test was applied to monitor the initiation and expanding of micro cracks in rock material. Theoretical analysis and data processing were carried out based on the theories of fracture mechanics and general rock mechanics, relations between the feature strength of three stages and the stress state were obtained, and a method was proposed for analyzing the brittle shear failure of rock material. The relationships of the Mohr-Coulomb strength theory, Griffith strength theory and Hoek-Brown criterion with the brittle-shear coupled strength model were discussed. Strength analysis of mixed granite in Shuichang slope was carried out by the brittle shear failure model, and the result of comparison shows strong correlation between test data and theory values.
Abstract: An activity model of vanadium slag was established according to the coexistence theory of slag structure. The influences of vanadium slag compositions and temperature on the activities and activity coefficients of FeO and V2O3 were analyzed based on the model. The effects of vanadium slag compositions and temperature on the distribution behavior of V between slag and semi-steel at the end point of vanadium extraction by converter were studied by experiments and calculation. It is shown that the activity and activity coefficient of FeO, which are at magnitudes of 10-1 and 100 respectively, increase with the increase of FeO and MnO contents but decrease with increasing V2O3, SiO2 and TiO2 contents in the slag; the activity and activity coefficient of V2O3, which are at magnitudes of 10-2 and 10-1 respectively, show opposite trends compared with those of FeO under the same conditions. The mass fraction of V usually ranges from 0.02% to 0.06% in semi-steel, increases with the increasing of temperature and V2O3, SiO2 and TiO2 contents but decreases with increasing FeO content in the slag. The distribution ratio of V between slag and metal phase is in the range of 100 to 500, decreases with increasing temperature and SiO2 and TiO2 contents but increases while the content of FeO in the slag increases. There is a critical V2O3 content that makes the distribution ratio of V between slag and metal phase reach maximum, the theoretical value is 23.77% and the experimental one is from 15% to 20%.
Abstract: High-temperature modification by iron tailings was performed to study its influence on the volume stability and cementitious properties of steel slag. The mineral constituents and microstructure of steel slag after the high-temperature modification were analyzed via X-ray diffraction (XRD), scanning electronic microscopy (SEM) and energy dispersive spectrometry (EDS). It is found that the content of f-CaO obviously decreases and the cementitious properties of steel slag improve through the high-temperature modification. Compared with raw steel slag, the mass fraction of f-CaO in steel slag decreases from 4.84% to 1.82% after modification with 20% iron tailings at 1 250℃ and the activity index increases up to 5.6% after 28 d. With an increase in the mass fraction of iron tailings from 10% to 30%, silicate mineral phases such as manganolite, akermanite and calcium magnesium pyroxene form in the modified steel slag. The high-temperature modification promotes the decomposition of RO phase, in which FeO transforms to magnetite (Fe3O4) simultaneously.
Abstract: The anode electrochemical behavior of N80 steel in different concentrations of chloride and bicarbonate solutions was studied by potentiodynamic polarization curves and dynamic electrochemical impedance spectroscopy (DEIS). It is found that N80 steel is passivated without Cl- when the concentration of HCO3- exceeds 0.03 mol·L-1. Cl- can greatly improve the critical value of passive concentration of HCO3- and the passive film is seriously damaged meanwhile. In the anode region, the pitting potential drops, the passive current density increases, and the passive potential region narrows with Cl- addition in the solution with the same HCO3- concentration. DEIS results correspond with the potentiodynamic polarization curves. According to the relationship between the polarization potential and electrical components in the equivalent circuit, the roughness and compactness of the passive film decrease with Cl- addition, and the increase in passive current density depends on the decrease in charge transfer resistance mainly.
Abstract: A deposition model of 15 particles onto a substrate was established using the finite element program ANSYS/LS-DYNA. Based on the multi-particle deposition model, the deposition behavior and morphology as well as the interface characteristic were predicted for different particles/substrate cases. Al and Cu coatings were prepared by cold spraying. The cross section of the coatings and the characters of particle deformation were observed by scanning electron microscopy and compared with the simulated results by the multiparticle deposition model. The results demonstrate that the multi-particle deposition model can predict the effect of process conditions on the deposition behavior, microscopic characteristic, and interface morphology for different particles/substrate cases. When the impact velocity is low, particle deformation is not sufficient, which easily results in holes at the junction of particles; however, the holes disappear gradually with increasing impact velocity. Compared with particles, for a hard substrate, the coatings/substrate interface is smooth, which weakens the interlock; while for a soft substrate, the substrate deforms severely to form jet-like metal, which squeezes into particles to increase the bonding.
Abstract: Scanning electron microscopy (SEM) and compressive tests at room temperature and elevated temperatures were used to investigate the effect of Ni/Ti atom number ratio on the microstructures and mechanical properties of Ni42+xTi50-xAl4Hf4 (x=0-7) alloys. It is found that Ni42+xTi50-xAl4Hf4 alloys are composed of NiTi and Ti2Ni phases. The size and volume fraction of Ti2Ni phase decrease rapidly and the precipitation strengthening effect weakens with increasing Ni/Ti values. At room temperature when the Ni/Ti ratio increases, the compressive yield strength (σ0.2) and Vickers hardness (Hv) of the alloys decrease, but the ductility increases. At elevated temperatures, for the alloys of Ni/Ti < 1, the precipitation strengthening of Ti2Ni phase plays the major role, resulting in a decrease of σ0.2 with increasing Ni/Ti values; but for the alloys of Ni/Ti > 1, the solid solution strengthening effect of Hf improves, and the uniform distribution of Ti2Ni is more favorable for the strength, leading to the increase of σ0.2 with increasing Ni/Ti values. The high-temperature yield strength is asymmetrical with a deviation from stoichiometry (Ni/Ti=1).
Abstract: The constant electric conductivity curves of solid solutions in the SrTiO3-La0.3Sr0.7TiO3-(La0.3Sr0.7)0.93TiO3 ternary system were obtained by estimating the electric conductivity of the solid solutions by a mass triangle model. Some typical compositions of the solid solutions were selected to verify the calculated results. The experimental values are consistent well with the predicted ones, demonstrating the feasibility of a mass triangle model in predicting the electric conductivity of mixed conductor.
Abstract: TiN-coated SiC particles were prepared by the combination of alkoxide-hydrolysis and ammonia-nitridation. The coated composite powder was consolidated by spark plasma sintering. The results indicate that alkoxide-hydrolysis in combination with ammonia-nitridation is a suitable technique to produce TiN-coated SiC particles. The TiN film is thin and continuous, and the TiN particle size is about 30 to 80 nm, which is favorable to improve the densification and enhance interfacial bonding between the reinforcement and the matrix. The electric conductivity of (SiC) TiN/Cu composites is in the range of 15.5 to 35.7 m·Ω-1·mm-2 and decreases with increasing SiC content. The TiN film and the formation of a TiN network in the matrix contribute to the enhancement of electric conductivity. Additionally, the electric conductivity of the composites is more close to data predicted by the P. G model.
Abstract: A three-dimensional finite-element thermal-stress model of slab continuous casting molds was conducted to predict the deformation of copper plates and the effect of cooling structure on the deformation. It is found that the deformation behavior of copper plates is mainly governed by cooling structure and thermal-mechanical conditions, the deformation amount is related to the geometry of the cooling system, and a small deformation mutation occurs in the copper-nickel boundary. The maximum deformation at the hot surface centricity of the wide face locates at 100 mm below the meniscus, but that of the narrow face locates at the meniscus and the terminal of water slots. There are significant curvature fluctuations on both sides of the copper-nickel boundary of the narrow face. The maximum deformation at the hot surface centricity increases up to 0.05 mm with a thickness increment of 5 mm for copper plates, and the impact is not obvious from the nickel layer and water slots; the maximum deformations are only depressed 0.01 and 0.02 mm with the increments of 1 mm nickel layer thickness and 2 mm water slot depth, respectively.
Abstract: Establishing an accuracy relationship between the convective heat transfer coefficient and cooling process is the key to improve the laminar cooling control model. The convective heat transfer coefficient and corresponding surface temperature were calculated by the finite difference method and the inverse heat conduction method. The effects of cooling water jet flow rate on the heat transfer coefficient and surface temperature was investigated when the cooling water jet flow rate varied from 0.9 to 2.1 m3·h-1. It is found that the convective heat transfer coefficient is a nonlinear function of the surface temperature during laminar flow cooling. Within a distance of 70 mm from the stagnation line, the cooling flow rate has no effect on the heat transfer coefficient and surface temperature. But outside 70 mm, the heat transfer coefficient ratio becomes smaller with increasing distance from the stagnation line. It is also shown that relatively good agreement is obtained between the calculated and measured curves.
Abstract: This article focuses on the ellipse problem in two-roll cross wedge rolling the hollow shafts with uniform inner diameter. Numerical simulation by a finite element method was performed to study the forming process and the stress-strain conditions of the hollow parts. It is found that the mismatching between radial compression and axial flow leads to easier tangential metal flow and growing up in the circumferential direction, which is the main cause for forming the ellipse. The study is useful to choose proper process parameters in two-roll cross wedge rolling the hollow parts.
Abstract: The measurement principle of a transient hot-plane method was introduced to improve the service temperature of the method. The sample temperature distribution of a filmless plane heat source during heating process was simulated based on the finite element method. The experimental apparatus was established and practical measurements for the thermal conductivity and thermal diffusivity of materials were made at an environment temperature of 27 to 829℃. The results show that the transient hot-plane method is effective for measuring the thermal conductivity of materials in a high temperature environment, which is applicable to actual measurements.
Abstract: A comprehensive mathematical model of pressure swing adsorption (PSA) for separating and enriching coal-mine ventilation air methane (VAM) was established, which based on the mass and momentum conservation laws. A typical experimental process for VAM separation and enrichment in an axial-flow adsorption bed was numerically studied using active carbon pellets. The detailed distributions of gas concentration and adsorbance in the bed were obtained, and the calculated results are in good agreement with the experimental ones. The methane separation and enrichment processes in different cases were contrastively studied by varying the adsorption pressure, desorption pressure and desorption temperature to reveal the PSA characteristics for VAM separation and enrichment.
Abstract: A CO2 process emission model was built to calculate the CO2 emission of iron and steel plants for total and each process. The total emission of a specific plant with the productivity of about 8 million tons per year is 15.61 million tons and the emission intensity is 1.85 t CO2 for per ton of steel. Calculation results show that the order from the highest emission to the lowest one is BF, coking, sintering, rolling, BOF, flux roasting, and pelletizing process; the BF process and coking process account for 58.83% and 11.25% of the total emission, respectively. The general emission factor (GEF) and carbon saturation index (CSI) were proposed to evaluate the relationship between energy consumption and CO2 emissions in iron and steel making. It is found that the reduction of CO2 emissions results from not only energy saving but also the CSI reduction; the CSI has a significant relationship with the energy structure, and the higher percentage of energy with a higher total CO2 impact coefficient in the energy structure (coke for example) will results in a higher CSI, which has negative effect on the reduction of CO2 emissions. Developing eco-industrial parks, optimizing the energy structure, and enhancing the energy transform function of iron and steel making all have significant benefit on the reduction of CO2 emissions.
Abstract: This paper focuses on the dissemination characteristics and the influence factors of warning in a social network. Under the guidance of complex adaptive systems and complex network theories, a dissemination model of warning by using the multi-agent software of Repast was built based on ER random network and WS small world network. A simulation was performed at different settings of social network structure and selection rules in source nodes. By analyzing the simulation results the dissemination efficiency of warning is obviously improved when the clustering coefficient is high or the source nodes are at a high level of connectivity.
Abstract: A generalized predictive control (GPC) law with a disturbance observer was presented for an induction motor. A controlled auto-regressive integrated moving average (CARIMA) model for the drive system of an induction motor was established by analyzing the dynamic equation. The proposed generalized predictive control law aimed to make the actual speed at the next sampling time tracking to the reference speed with optimal characteristics, and the load torque was considered as an unknown disturbance, which could be estimated by a nonlinear observer. In combination with a direct torque control system, the GPC algorithm was applied to configure the torque reference. The stability of the system can be achieved by simple design parameters. Simulation and experimental results prove the effectiveness of the proposed controller.
Abstract: A design scheme of a novel ternary adiabatic JKL flip-flop was presented by research on multi-valued logic, adiabatic circuits, and the structure and working principle of ternary flip-flops. In the scheme, firstly, the theory of three essential circuit elements was taken as the guide, the component-level expressions of the ternary adiabatic JKL flip-flop were derived, and the corresponding circuit structure was realized by adopting MOS transistors with different thresholds. Secondly, an adiabatic novenary asynchronous counter was further designed by applying the ternary adiabatic JKL flip-flop and the ternary adiabatic literal circuit. Finally, HSPICE simulation results verify that the proposed circuits have correct logic function. Compared with a conventional ternary JKL flip-flop and a novenary asynchronous counter, the average energy consumption of the designed circuits is both saved more than 75%.
Abstract: Multiple indirection arrays often exist in one iteration, which is involved in irregular loop applications. A formal description of the hypergraph arrays was presented to solve this problem. Besides, three hypergraph-based data reordering algorithms (hypergraph-based non-repetitive coding data reordering algorithm, hypergraph-based backtracking search data reordering algorithm, and hypergraph-based partition first and then backtracking data reordering algorithm) and two hypergraph-based iteration reordering algorithms (hypergraph-based non-repetitive coding iteration reordering algorithm and hypergraph-based backtracking search iteration reordering algorithm) were put forward. Experiments were performed on computational fluid dynamics, which was a representative irregular application. It is indicated that data locality is improved by the single reordering algorithm, with the execution speed increasing by 25.4%. The combination of the data reordering algorithm and the iteration reordering algorithm demonstrates the best performance, with the average hit rates of level- 1 and level- 2 cache reaching 91.7% and 96.5%, respectively
Abstract: According to the features of digital images, a kind of three-dimensional scrambling and encryption algorithm was proposed based on two-dimensional scrambling transformations in a finite integer domain, affine transformations, and integer lifting transformations. This algorithm applies to images with any length and width or at any length-to-width ratio. The feasibility that some parameters of the transformation matrix are negative integers or decimals is taken into account, and the method of parameter setting is explicitly shown. Real number is used in the algorithm, which expands the space of parameters, scrambles the pixel positions and changes their values, makes the scrambling result better, increases the periodicity of scrambling, and improves the security of digital image transformations.
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
