Abstract: The representation elementary volume (REV) was introduced on the base of the hypothesis of macro-continuity of rock masses. Firstly, the basic mechanical parameters of rocks were measured by the conventional triaxial tests and unloading resilience tests, and the mechanical parameters of rock interfaces and joints were obtained by direct shear tests. Secondly, the existence and the dimension of REV were determined by the method of numerical simulation testing according to the rule that the mechanical character can get to be stable when the volume of rock masses are larger than the dimension of REV. Finally, the mechanical parameters of rock masses were calculated by numerical simulation analysis of a three-dimensional model based on the dimension of REV.
Abstract: A series of splitting tensile tests were conducted by using an INSTRON testing system to investigate the effect of cement-tailings ratio on the properties of backfill. Based on experimental data, the evolvement laws of energy dissipation under different conditions were presented and some correlative formulae were proposed to describe the relationship between energy dissipation and influencing factors, It was found that tensile failure acted as the dominant factor for eventual failure of backfill and energy was dissipated less for tensile failure. Several optimized measures were suggested to reduce, even eliminate, the tensile state in backfill. Control blasting of periphery-holes and decoupling charging should be used to reduce under-excavation and over-excavation by optimizing the propagation of detonation wave. Crucial parts, where projects are disposed and stress concentrates, should be reinforced by special backfill with large cement-tailings ratio to improve the energy absorption capacity of the structure.
Abstract: The buckling behavior of cylindrical shells with large rectangular opening was analyzed by the finite element method. Firstly, eigen value buckling was carried out to predict the buckling mode and critical load. Secondly, the load-displacement response of the structure was computed with geometrically nonlinear analysis, and the orthogonal design method was adopted to discuss the influence of geometric parameters on the buckling load. The considered parameters include opening width, opening height, location in the longitudinal direction, and radius-to-thickness ratio and height-to-diameter ratio of the shell. The result shows that the upper limit buckling load of a cylindrical shell with rectangular opening is much less than the lower limit value of a perfect cylindrical shell, and the buckling load of a cylindrical shell with rectangular opening is mainly dependent on the radius-to-thickness ratio of the shell. The critical load declines rapidly when the radius-to-thickness ratio of the shell increases.
Abstract: Based on the information of decarbonization reaction in a convertor continuously obtained with gas analysis technology, the critical carbon content at the decarbonization rate change point,[C]d, in BOF blowing process was researched by back-calculation method. The results show that the effect of bath stirring energy on the critical carbon content[C]d is very obvious near the refining end point, and the critical carbon content[C]d decreases with increasing stirring energy due to the increase in bottom blowing flowrate; but when the stirring energy is greater than a certain value, the influence of bath stirring energy on the critical carbon content[C]d is very small. Top oxygen blowing flowrate has important effect on the critical carbon content[C]d for a top blowing converter, and with the increase of oxygen blowing flowrate the critical carbon content[C]d decreases.
Abstract: A study of extracting iron from nickel residue was done by smelting reduction method. The experiments were conducted to investigate the effect of slag basicity, melting time and temperature on the iron recovery ratio. XRD analysis indicates that the nickel residue is composed of FeSiO3 and glassy silicates, so it is impossible to reach the target of FeO content by regular ore-dressing method except by smelting reduction method. Experimental results show that the recovery ratio of iron increases with increasing the content of CaO added, melting temperature and time. The key reduction reaction is firmed as (FeO) + C(s) →[Fe] + CO↑ by comparing Gibbs free energies at different temperatures from 1450 to 1600℃. The batch of nickel residue 100 g, CaO 34.7 g, CaF2 4.04 g and coke 8.5 g was the best formula in this study, and it was indicated that after melting at 1500℃ for 180 min, the slag and iron were well separated and the recovery ratio was up to 96.32% for this batch.
Abstract: 3.5% NaCl (mass fraction) aqueous solution as corrosion medium was dropped onto the surfaces of low-carbon ferritic steel, 09CuPCrNi steel and low-carbon bainitic steel to form thin liquid films. Initial corrosion of the steels was observed by metallographic microscope. Selected attack along grain boundaries occurred in both low-carbon ferritic steel and 09CuPCrNi steel, while this did not occur in low-carbon bainitic steel. The electrochemical impedance spectrum and polarization curve of the steel matrixes indicate that low-carbon bainitic steel exhibits the highest polarization resistance and the lowest corrosion current, so the initial corrosion rate of fine crystalline low-carbon bainitic steel was lower than that of the other two steels.
Abstract: The influence of deformation during stretch reducing, C and N contents on the microstructure of medium-carbon V-Ti-N microalloyed steels for oil-well tubes was investigated with a Gleeble-1500 simulator. The results show that the volume fractions of ferrite in HCLN steel with deformations of 20%, 40% and 60% at 800℃ are 17.2%, 19.7% and 29.9%, respectively. The amount of ferrite in HCHN steel with an N content of 2.3 × 10-4 is almost equal to that in LCLN steel with a C content of 0.26%, and 1.7 times that in HCLN steel with an N content of 1.1 × 10-4. However, the size of ferrite grains in HCHN steel is about 3μm, the smallest among the experimental steels. It is obvious that increasing deformation and N content is beneficial to the amount of ferrite, and it is more effective that deformation and N are used simultaneously. According to analyses, when the degree of deformation enlarges, defects in non-recrystallized austenite grains increase, which is helpful to provide plenty of nucleation sites for intragranular ferrite. While increasing the content of N to 2.3 ×10-4, second-phase precipitation is promoted, the amount of ferrite increases, and ferrite grains are refined simultaneously.
Abstract: The effects of cooling rate, deformation temperature and reduction on the microstructure and martensite/austenite (M/A) islands in a Nb-V-Ti micro-alloyed steel were studied by Gleeble thermal-mechanical simulation tests and microstructural observations. The results show that an increase in cooling rate and a decrease in deformation temperature can refine the mierostructure, reduce polygonal ferrite and enhance acicular ferrite (AF) in the steel. Under different controlled rolling processes, there is a certain amount of M/A island structure in the matrix, while the effect of deformation temperature on the M/A is small. Appropriately increasing the cooling rate and reduction can reduce the volume fraction of islands and make them be refined and dispersed, so the proper combination of AF and M/A can be obtained by controlling deformation parameters to improve the properties of the steel.
Abstract: Clad plates of 25Cr5MoA steel/micro-alloyed steel/Q235 steel were prepared with composite slabs heated to the rolling temperature between 950℃ and 1 100℃, held at each temperature for some time, and then rolled one pass under the reduction between 50% and 65%. The interfacial bonding strength was measured by shearing testing and the interfacial metallographic microstructures were observed by optical microscope. The results show that the rolling temperature between 950℃ and 1 100℃ is favorable to the bonding of the steels. Pass reduction has effect on the bonding strength, and after the pass reduction reaches some value the bonding strength degrades with increasing pass reduction. Rolling temperature is crucial to the bonding strength, and as the temperature rising, the bonding strength increases gradually under the same reduction. The bonding strength reaches the maximum value at a rolling temperature of 1 100℃ and a pass reduction of 50%.
Abstract: The variation in hardness of 80Co-20Ti intermetallic compounds with aging time was investigated, and the change in yield strength of aged 80Co-20Ti intermetallic compounds undergoing aging and containing precipitates with temperature was tested. Transmission electron microscope (TEM) observations reveal that the precipitates are L12Co precipitates with simple fee crystal structure. Although the hardness of the precipitates is less than that of Co3Ti matrix phase, the Co3Ti hardens appreciably by fine precipitation of disordered fee Co-rich phase. The precipitates are perfectly coherent with the matrix lattice at the beginning of aging. The shape of the precipitates is platelet and is nearly parallel to the[100]planes of the L12-ordered matrix. It is indicated that the interaction between L12Co precipitates and deformation dislocations is attractive interaction and this type of interaction plays an important contribution to the hardening. The strengthening mechanism deduced from the attractive interaction between the soft precipitation and hard matrix was also discussed.
Abstract: The microstructure and mechanical properties of two high Nb containing TiAI alloys with different Mn contents, Ti46Al8Nb2Mn0.2B and Ti46Al8Nb1.3Mn0.2B, were studied. XRD and SEM results show that the Ti46Al8Nb2Mn0.2B alloy obtains duplex microstrueture with a few brittle 13 phases after hot isostatic pressing (HIP) and cyclic heat treatment. By thermostatic treatment in two-phase area for long time after HIP, no β phases were found in the microstructure of the Ti46Al8Nb1.3Mn0.2B alloy. Tensile test shows that the mechanical properties improve with decreasing Mn content, and the elongation, yield strength and breaking strength of the Ti46Al8Nb1.3Mn0.2B alloy are 2.4%, 548 MPa and 660 MPa, respectively. The fracture morphologies indicate that the fracture of the two alloys at room temperature belongs to brittle cleavage fracture.
Abstract: The oblique crack arrest of 7A04 super hardness aluminium was studied by super pulse current discharge with home-made equipment ZL-2. Under the super impulse current discharge, there is a strong detouring phenomenon at the crack tip. The metal melt around the oblique crack tip passivates the crack tip and inhibits the cracking trend of main crack source. The microstructures of the aluminium alloy before and after crack arrest were observed by metallographic microscope, and the fracture morphologies were compared macroscopically and microcosmically. Tension tests of samples with an oblique crack before and after crack arrest were done by using a PC-control universal tester. The results indicates that on the moment of crack arrest, the metal around the crack tip melts, the microstructure at the crack tip appears super refine, the work of crack expansion increases, and the tensile mechanical properties of specimens are improved.
Abstract: The relation between preparing parameters of magnesia-zirconia bricks and their resistance to RH slag corrosion was studied by contrasting the slag resistance behaviors of magnesia-zirconia bricks and magnesia-chromite bricks and by a simplified model. The preparing parameters that influence the RH slag resistance properties of magnesia-zirconia bricks, such as grain mixture ratio, agglutinant, sintering temperature, zirconia content, and variety of zirconia, were analyzed by orthogonal experimental design (OED). The results indicate that sintering temperature and zirconia content are two key influencing factors. The effects of sintering temperature and zirconia content on the ratio of infiltrate depth were further examined by the steepest ascent method and central composition design (CCD), and a statistic analysis model of resistance corrosion of magnesia-zirconia bricks eroded by RH slag was built.
Abstract: In order to investigate the phase transition of silicon nitride (Si3N4), α-Si3N4 with Y2O3 and Al2O3 as additives was sintered under 5.2-5.7 GPa at 1 100-1300℃ for 15 rain. The sintered samples were analyzed by X-ray diffraction, scanning electron microscopy and density measurement. The results showed that α→βphase transition started in 1 100-1200℃ and the ratio of transformation from a to β phase increased with increasing temperature and pressure, α-Si3N4 was completely transformed to β3-Si3N4 under 5.7 GPa at 1300℃. The β-Si3N4 was composed of elongated β-Si3N4 rod crystals with disordered orientation and had intergranular interlocks and uniform and compact microstructure. Pulled-out crystal grains on the fractured cross sections were obviously observed by SEM. The boundary equations of the two phases were roughly fitted on the base of obtained data. The related mechanism of phase transformation was discussed.
Abstract: Ni/polyacrylate conductive coatings were prepared by utilizing magnetic field to control the alignment of nickel particles in acrylic emulsion. Their surface morphologies with and without the application of magnetic field were analyzed by SEM. The effect of magnetic field on the conductivity and shielding effectiveness of the coatings was studied. In combination with a dynamic model the influencing factors on the time of magnetic-field-induced-alignment (MFIA) was discussed. The results reveal that MFIA helps to generate a yarn-shaped microstructure in the coatings, which improves their conductivity. The percolation threshold of the resulting coatings decreases from 5,6% to 3.0% in volume fraction. Compared to the unaligned, the shielding effectiveness curve presents an even distribution after MFIA, and the electromagnetic shielding effectiveness is optimized. Alignment time can be controlled by changing the system viscosity and the applied magnetic intensity.
Abstract: The standard κ-ε model, VOF multiphase flow model and porous zone model were adopted to simulate residual slag in a blast furnace hearth under different deadman conditions. It is shown that the residual slag almost concentrates in deadman and the coke distribution in the peripheral region of deadman is the key factor influencing the total residual rate of slag. Deadman state below the lowest slag-iron level has little effect on the total residual rate of slag. Since the liquid iron and slag velocity near the taphole region is much greater than that in deadman, a downward-to-taphole gas-slag interface is formed. The taphole is stopped when gas begins to blow out, which causes much slag to have no time to drainage out. Improving the permeability of deadman is a very effective method to decrease the residual rate of slag.
Abstract: The effect of the angle of submerged entry nozzles, casting speed, and cross-section width of slabs on the surface fluctuation in a mold of Anyang Iron & Steel was researched with the VOF model of commercial software ANSYS CFX10.0. The results show that with the mold width increasing from 1 800 mm to 3 250 mm, the average wave height of liquid level in the mold decreases significantly. When the width is 1 800 mm, the average wave height of the mold flux-molten steel interface is 5.33 mm; when the width is 3 250 mm. the average wave height is 7.08 mm.
Abstract: Full-scale water modeling experiments were carried out to investigate the transient fluid flow in a CSP funnel-shaped mould under a bilateral hole submerged entry nozzle (SEN). The results show that molten steel level is unsteady and the level fluctuation has a periodical exacerbation, which is called meniscus dynamic distortion (MDD). The relationship between process parameters and MDD was discussed. Tracer experiments were used to study the flow characteristic of molten steel in the mold. It is concluded that the turbulent kinetic energy assembling and rapid dissipating from bottom to meniscus cause the MDD.
Abstract: Aiming at two kinds of coupling problems in flatness control of a UCMW cold tandem mill, the coupling between edge drop control and flatness control and the controlling efficiency coupling between work roll bending and intermediate roll bending, the coupling degree parameters is defined to quantitatively express the coupling degree. A method for decoupling the two kinds of coupling problems was proposed by designing the end contour of intermediate rolls. The end contour of intermediate rolls was designed for a 1550UCMW cold tandem mill. Simulation results showed that the designed end contour of intermediate rolls decoupled the two kinds of coupling relationships in certain degree, and the mill could be further optimized to improve its flatness control performance for enhancing the physical shape quality of products.
Abstract: The work roll grinding contour of non-oriented silicon steel hot rolling is dependent on the work roll thermal contour heavily which will lead to an unexpected initial work roll contour under normal roiling condition. To resolve this problem, considering the condition of non-oriented silicon steel rolling, a work roll temperature field model during rolling was constructed by using the 2-D finite difference method and a work roll temperature field model after rolling under air and spray mixed cooling condition was developed by using the finite element software ANSYS. Based on these models, the work roll temperature field and thermal contour through the whole non-oriented silicon steel rolling process were researched numerically, and a hot grinding mathematical model and its schedule were proposed and applied in industrial production. Under the same condition, after applying the new work roll hot grinding mathematical model and its schedule to non-oriented silicon steel strip rolling of 1700 mm hot strip mills, the qualification ratio of crown and wedge increased from 67.39% to 74.57%.
Abstract: The validity of physical programming based on preference design was studied from mathematical aspects. By both defining and quantifying of preference, four classes of preference functions and an aggregate preference function were constructed by using numerical method, and a mathematics model of physical programming was proposed. The result of example analysis accorded with the design of different preference areas.
Abstract: An experimental method for measuring the constitutive relation of granular flow was presented. Granular chute flow was described as a non-Newton fluid, and its constitutive relation was computed on the base of the velocity distribution calculated by the throwing motion of granules when being out of a chute. A model of granular chute flow was employed, which indicates that the velocity obeys exponential distribution and the flow rate is a function of chute angle and flow thickness. From the theoretical analysis of wheat granule chute flow by using the constitutive relation from experiment, the relative error of the predicted volume flow rate is less than 13% compared with experimental data.
Abstract: Parallel flatness pattern recognition based on a binary tree hierarchical back propagation (BP) model and Legendre orthodoxy polynomial decomposition was presented aiming at the illegibility in physical meaning and poorness in robust stability of traditional flatness defect pattern recognition by the least squares method (LSM) proximity algorithm and the low accuracy of a common BP neuron network. It reduces the prediction range of each network and uses more networks for degree elevation. Experimental results show that the system performances are improved not only in robust ability but also in precision.
Abstract: An open-closed loop iterative learning controller was proposed to control the mover of a permanent magnet linear synchronous motor (PMLSM) servo system to track expectation linear position. The two-dimensional model of PMLSM and the convergence of the iterative learning linear servo system were analyzed in detail. The forgetting factor was optimized by reducing the trace of the input error covariance matrix. This factor is able to modify the iterative learning law of control input. The error signal of the feed-forward learning controller was filtered by a zero-phase FIR digital filter. Experiment results demonstrate that the filtered-version iterative learning controller with forgetting factor can surely improve the performance of the servo system in iterative learning process and effectively suppress the ripple of end force. The system has good learning convergence speed, dynamic response and control precision.
Abstract: The delay-dependent robust stabilization of an uncertain linear system with both state and input delays was discussed. By combining the matrix decomposition idea with the Lyapunov-Krasovskii functional method, adding an appropriate zero term to the deviation of V, and introducing a free weight matrix, a delay-dependent sufficient condition based on linear matrix inequality was derived to ensure the system's robust stabilization via memoryless state feedback, and a specified controller design method was proposed. A numerical example was given to illustrate that the new results were less conservative than the present literatures.
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
