Abstract: For rock specimens with initially random material imperfections in uniaxial plane strain compression, the effects of initial cohesion and internal friction angle on the failure processes were modeled using FLAC. FISH functions were used to generate random imperfections and to remember the number of failed elements. For the intact rock exhibiting the linear strain-softening behavior beyond the occurrence of failure and then the ideal plastic behavior, the failure criterion is a composite Mohr-Coulomb criterion with tension cut-off. The imperfection undergoes the ideal plastic behavior beyond the occurrence of failure. As the strength parameters (initial cohesion and internal friction angle) increase, the stress drop and incremental axial strain from the peak stress to the residual stress increase; the occurrence of shear fractures intersecting the specimen is later and the final number of yielded elements decreases. For the intact rock with higher strength parameters, after all imperfections fail it does not fail immediately; instead, when the axial stress reaches a certain value it starts to yield and the increase in the number of failed elements is less apparent beyond the peak stress. In the loading process, the acoustic emissions are apparent in three stages. The first stage, the second stage and a majority of the third stage appear at pre-peak. Prior to the peak stress and in the third stage, the increase in the acoustic emissions results from the extension, coalescence and propagation of imperfections and the competition among imperfections. Higher strength parameters of the intact rock cause the third stage to be wider and the number of acoustic emissions to be lower, suggesting that the failure is more progressive and the failure duration is longer.
Abstract: The quality characteristics of mine drainage with high turbidity were described on the basis of investigating the particle size distribution, the characteristics of suspended particle surface, and the coagulating characteristics in mine drainage, and the influencing factors on the affinity between coagulants and suspended particles in mine drainage treatment were analyzed. The results show that the suspended particles in mine drainage mainly consist of coal and rock grains with small size and negative electric charge which make them hard to naturally subside. As the coal rank goes to higher, the wettability of coal grains and the affinity between coal and coagulants decreases gradually.
Abstract: Monte Carlo simulations with Potts model were performed to investigate the process of normal grain growth starting from an initial microstructure, the grain size distributions of which could be well described by the Weibull function with a parameter β=3.47. The result show that a parabolic law is observed in grain growth and the simulation time exponent of grain growth n=0.501, which is very close to the theoretical value for grain growth n=0.5, is attained. The complete process of normal grain growth simulation includes transition period and steady state period. In transition period, the grain size distribution is changed rapidly from the Weibull distribution with β=3.47 to the Weibull distribution with β=2.76. In steady state period, the grain size distribution maintains the Weibull distribution with β=2.76. The mean grain face number <f> increases with the increase of time and in the late steady state period <f> approaches soine steady value. The Lognormal function fits the grain face number distribution well and the scope of the individual grain face number is 3-43.
Abstract: The effects of pulse current on the mechanical properties of spherical graphite iron, the graphitization of cementite and the transformation of ferrite were studied during the high-temperature graphitization of spherical graphite iron with pulse electric current as an assistant way. The results show that the tensile strength and the hardness of the specimen decrease, while the elongation increase. SEM micrographs of the specimen show that electropulsing promotes greatly the high-temperature graphitization of spherical graphite iron and the transformation of ferrite. The acceleration of cementite decomposition and the transformation of ferrite result from the increase of graphite nucleation rate by electropulsing.
Abstract: Based on the analysis of thermodynamics and dynamics for austenization during intercritical annealing of a dual phase steel; an austenization model was established and solved by using the explicit finite volume method at two austenite temperatures of 740℃ and 780℃. The simulated results show that the initial stage of austenite growth is controlled by carbon diffusion in austenite and reaches paraequilibrium quickly, and the austenization rate in this stage is very fast. The late stage of austenite growth is controlled by manganese diffusion in ferrite. As the diffusion rate of manganese is several orders of magnitude slower than that of carbon, this stage lasts for thousands of seconds. When the diffusion flux of manganese in each phase is equal, austenite stops growing. But manganese continues its transfer from ferrite to austenite in order to achieve its homogenization in each phase.
Abstract: The morphology, chemical composition, size and type of inclusions were investigated by experiment and thermodynamic calculation in a micro-alloyed steel deoxidized by Ti, and the structure of this steel was analyzed. The results show that grains are fine after adding Ti in the steel, the deoxidation product of Ti become the nucleus of TiN, or Al2O3 becomes the nucleus of the deoxielation product of Ti in solidification of liquid steel. After adding Ti, inclusions are finely distributed in the steel, and grains are fine by using the dispersion of fine inclusions as intragranular ferrite nucleated sites.
Abstract: A multifunction continuous annealing simulator (Multipas) was employed to numerically simulate the continuous annealing process for a low silicon HSLA steel sheet of 380 MPa grade in yield strength. The effects of annealing process on the microstructure and mechanical properties of low silicon HSLA steel were studied at annealing temperatures of 820, 800, and 780℃; and annealing speeds of 60, 120, and 160 m·min-1. The result indicates that the grain sizes of microstructure are similar at different annealing temperatures and different annealing speeds. The higher strength of low silicon HSLA steel can be gained when it is annealed at a lower annealing temperature and a higher annealing speed. The annealing speed affects the mechanical properties more significantly when the annealing temperature is in a higher level.
Abstract: XRD, TEM, SEM and tension testing were used to investigate the microstructure evolution and mechanical hardening of 18-18-0.5N high-nitrogen austenitic stainless steel during cold rolling. The experimental results show that there is no sign of deformation-induced phase transformation. A inflection point of microstructure and mechanical properties was found at 43.8% reduction. An excellent predicting equation of yield strength to strain was presented.
Abstract: ABSTRACT The corrosion behavior of 7A04 aluminum alloy in 1 mol· L-1 sodium sulfate solution was investigated by a thin electrolyte layer equipment. The surface morphology was observed by scanning electron microscope (SEM). The corrosion products were analyzed by energy dispersive X-ray detector (EDX) and X-ray photoelectron spectroscopy (XPS). The electrochemical character of 7A04 aluminum alloy was studied by electrochemical impedance spectroscopy (EIS). It is shown that the corrosion is not uniform, and the corrosion product at the edge is more than that at the center. The corrosion products of the specimen surface mainly are Al(OH)3 and aluminum sulfates. EIS measurements indicate that the corrosion rate of 7A04 aluminum alloy under the thin electrolyte layer of 110μm is the biggest in the initial stage (0~96 h). But in the later stage of corrosion (96~168 h), the corrosion rate in the bulk solution is the biggest.
Abstract: The room temperature behavior of the hydrogenated Ti-6Al-4V alloy was investigated by compression test ences of hydrogen on the microstructure and the morphology of fracture were analyzed. The correlation between room-temperature plasticity of the hydrogenated Ti-6Al-4V alloy was explored. The results show that the hardening effect of the hy-drogenated Ti-6Al-4V alloy is enhanced due to the solution strengthening function of hydrogen, but the addition of appropriate hydrogen to the Ti-6Al-4V alloy can dramatically decrease the yield strength and elastic modulus and can increase the compression ratio of the alloy with the α + β binary microstructure. The compression ratio wiU fall largely when there are coarse β grains in the alloy. Moreover, the addition of hydrogen can promote the generation of orthorhombic martensite α″. The fracture of the hydrogenated Ti-6Al-4V alloy generally displays as compounded one of ductile or brittle intercrystalline fracture and transcrystalline fracture.
Abstract: The influences of hydrogenation on the particle morphology and surface state, microhardness, particle microstructure, phase component and pressing property of TCA alloy powder were studied by means of SEM, powder inlaid, XRD and die forming. The results show that hydrogenated TCA alloy powder possesses irregular morphology, which is composed of bright a phase and dark β phase and exhibits lamellar structure, needle-like and lath-shaped structure. With the increase of hydrogen content, the particle morphology of hydrogenated TCA alloy powder was mostly irregular, but the microhardness showed a decreasing trend, α phase decreased and β phase increased gradually. When the mass fraction of hydrogen was 0.32wt%, α″ phase appeared, and when the mass fraction of hydrogen reached 0.42% or 0.46%, the particle microstructure was lath-shaped (δ-TiHX) obviously. The compressive property of hydrogenated TCA alloy powder became better, the forming property got worse gradually with increasing hydrogen content, and the pressing property of the powder with a mass fraction of hydrogen of 0.46% is the best.
Abstract: The influence of role sealing produced by plating Cu at low current density on the corrosion resistance of the anodized AZ31 magnesium alloy was studied. After anodization, AZ31 specimens were treated as a cathode with low current density in a traditional solution for Cu electroplating. The experimental results of SEM, EDS and XRD show that after such treatment at low current density, Cu is deposited in the porous layer of anodized film. The polarizing curves measured in 3.5% sodium chloride solution show that after plating Cu at low current density the corrosion potential of the anodized AZ31 magnesium alloy increases, and its corrosion current density reduces correspondingly, which indicate that the corrosion resistance of the anodized AZ31 magnesium alloy increases.
Abstract: A Fe-Ni alloy coating was prepared in a sulfate bath by electrodeposition. The influences of process parameters, such as Fe2+/Ni2+ molar ratio, CeCl3 concentration, ascorbic acid concentration, bath temperature, pH, cathodic current density and deposition time, on the ferrous content in the coating were studied. An optimum process condition was determined for the electrodeposition of invar alloy. The coating obtained under the optimum condition was analyzed by EDS, XRD and TEM. The results showed that the mass fractions of Fe and Ni in the coating were 61.8%-62.1% and 37.9%-38.1%, respectively, similar to those of invar alloy, and the coating was solely composed of nanocrystalline γ solid solution.
Abstract: ABSTRACT Fe/Co particles encapsulated in carbon nanotubes (CNTs) were prepared by anodic arc discharging plasma. Transmis-sion election microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) were used to character the structure and magnetic properties of the products. TEM results show that CNTs have little impurity and uniform size, and the particles encapsulated in carbon nanotubes are Fe/Co particles with good continuity. The magnetic properties of CNTs encapsulated with Fe/Co particles are greatly improved, and the saturated magnetization σs, remanence σr, and coercivity Hc of the sample are 17.30A·m2·kg-1, 3.96A·m2·kg-1, and 31521.60A·m-1, respectively.
Abstract: Tl2Ba2CaCu2O8(TBCCO) films were deposited on LaAlO3 (LAO) substrates by magnetron sputtering. The results of SEM and XRD show the films have high quality. The resistive transitions of the TBCCO/LAO were investigated at different magnetic fields using a standard four-probe method. The resistive transition broadening of TBCCO/LAO can be seen and it is stronger with the magnetic field perpendicular to the films than with the magnetic field parallel to the films. The thermally activated flux flow theory was used for analyzing the resistive transition broadening. The anisotropy of the films was discussed by analyzing the resistive transition.
Abstract: It is found that CaO-ZrO2-TiO2-BN system can stably exist at 1823 K from the overlapped phase stability diagram of Ca-O-N, Zr-O-N, Ti-O-N and B-O-N systems. XRD analysis results indicate that oxides in the system form complex compounds or solid solution. The phase diagram of CaO-ZrO2-TiO2 was Calculated by FactSage software, and the results show that the system can be controlled in solid section at high temperature through controlling TiO2 quantity. During continuous casting, BN cannot be oxidized by O2 or[O] because of the existence of[Al] in molten steel.
Abstract: Concrete and paste were immersed in a 3.5% NaCl solution for 650 d after they were quickly carbonated for 0, 14 and 28 d. The free and total chloride contents in different depths of concrete were tested to calculate the chloride apparent diffusion coefficient and the chloride binding capacity. The pore structure and corrosion production of paste attacked by different corrosion regimes were analyzed by mercury intrusion porosimeter (MIP) and differential thermal analysis (DSC), respectively. The results indicate that the chloride content and the chloride apparent diffusion coefficient increase after quick carbonation, however the chloride binding capacity of concrete reduce simultaneously; and the carbonation influence increase with time. Quick carbonation of concrete coarsens its pore structure that the capillary pore (≥ 30 nm) amount of paste increases by 11% and the most probable pore size increases by 17 nm, but it decreases the Friedel'S amount in concrete and reduces the chemical chloride binding capacity of concrete.
Abstract: The calculating models of mass action concentration for electrolyte aqueous chloride solutions KBr-H2O, NH4Br-H2O, and ZnBr2-H2O were founded at 298.15 K to calculate the molalities before saturation according to the ion and molecule coexistence theory and the mass action law. The calculated mass action concentration is based on pure species as the standard state and mole fraction as the concentration unit, and the reported activities are usually based on infinite dilution as the standard state and molality as the concentration unit. Hence, the calculated mass action concentration must be transformed to the same standard state and concentration unit. The transformation coefficients between calculated mass action concentrations and the reported activities of the same component fluctuate in a very narrow range. Thus, the transformed mass action concentrations not only agree well with the reported activities, but also strictly obey the mass action law. It is indicated that the new developed models can embody the intrinsic structure of the investigated three electrolyte aqueous solutions. Electrolyte aqueous solutions have characters of ideal solution under the assumed condition. The results also show that the mass action law has its widespread applicability to electrolyte binary aqueous solutions.
Abstract: On the basis of the masteries for the aluminum oxide ore pulp drying and calcination, a mathematical model was developed for simulating the process of heat transfer and the calcination of two-phase flow in a new type furnace designed by Zhongzhou Branch Company, China Aluminium Corporation Limited. The fields of velocity, temperature and pressure of the two-phase flow and the reaction time were gained by optimizing calculation under the condition of different operational parameters and geometric parameters. The effect of vent position, velocity and atomization particle diameter on the drying and calcination technology of aluminum oxide ore pulp was discussed.
Abstract: An expression of combined heat transfer coefficient was obtained based on the heat transfer analysis of a blast furnace copper stave, and the combined heat transfer coefficients at different gas temperatures were obtained through the thermal test in an experimental furnace. A three-dimensional mathematical model was established for the copper stave, and the distribution of temperature field was simulated under different boundary conditions. Comparing the result of simulation with that of the thermal test, the combined heat transfer coefficient should not be a constant but a variable dependant on gas temperature. The distribution of heat flux density in the copper stave and the change range of slag thickness on hot-face were derived from the result of simulation.
The 3-D finite element model of an H-beam in straightening process was established by using the processing parameters of a nine-roller cantilever straightener with variable roller spacing. By analyzing the regularity of stress distribution in the H-beam's cross-section during straightening, the character of stress variation was observed which is similar to the stress-wave that spreads from outer-flank to inside-flange, as well as from the two-tips of flange to the middle of web. The simulation result indicates that, the straightening effect is decided by the longitudinal normal stress and the longitudinal shearing stress also affect the distribution of crosssection equivalent stress, while the R comer of web and the area of web contacted with the fillets of straightening rollers suffer from high stress during rear straightening process, and residual stress can also been found after straightening finished.
Abstract: The exchange heat boundary conditions of an accelerated controlled-cooling system (ACC) were decided, and a finite element model of temperature and stress field was constructed. The calculated result of temperature field was proved by testing data, and the stress field of steel plates was computed by using the coupling method. Finally, the effects of parameters such as header combination, running speed and cooling medium temperature on the heat residual stress were analyzed.
Abstract: A kind of chaotic synchronized secure communication scheme with time-varying parameters was proposed to solve the problem of parameter sensitivity reduction caused by chaotic synchronization, which further degrades the security. The stability of synchronization was then proved. It is unique that the chaotic activities obey the strange attractor globally, while in local they move randomly. As a result, the chaotic obits are more complex, the parameter sensitivity degree rises from 1 to 10. It makes the system hard to be broken by exhaustive attack and phase space restructuring. When the active-passive decomposition method is used, the secure communication scheme has no synchronized error. Simulation results indicate the effectiveness of the method. It is applicable to a kind of continuous chaotic system.
Abstract: The bound of a kind of three-dimensional chaotic system was estimated. Firstly, under the condition of -1 ≤ c<0, the theorem about an upper bound estimate of two variables was given by parameterization and proved. Secondly, the theorem about an upper bound estimate of three variables was proposed and proved. Finally, the actual parameter bounds of the three-dimensional chaotic system were estimated and their numerical simulations were done.
Abstract: To improve the accuracy of multi-relational Naive Bayesian classifiers, the existing pruning methods were discussed and the attribute filter criterion was upgraded based on mutual information to deal with multi-relational data directly. On the basis of the tuple ID propagation method and counting methods towards tuple, the filter method based on extended mutual information was given, and a multi-relational Naive Bayesian classifier based on mutual information (MI-MRNBC) was implemented. Experimental results show that, in a multi-relational domain, with the help of the attribute filter based on extended mutual information, the classifier can give a better accuracy without the increase of time complexity. In extraordinary instances, the multi-relational classification degenerates into a single relational one, which extremely decreases the cost of classification.
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
