Abstract: Detection of a goaf by laser-scan technology to build a 3D visualized model and to obtain the goaf's 3D space position and shape, is an important part for comprehensive management of the goaf's accidents. Multiple probes from multiple orientations are usually needed to obtain a goaf's 3D shape because of its complexity. How to construct a triangular mesh model from splice unorganized points by multiple probes is the key technology of a goaf's 3D modeling. A spherical projection triangulation algorithm is proposed for laser-scanning splice unorganized points of a goaf in this paper. Firstly, projected points are got by a chosen sphere center and projecting in-situ points onto the sphere. Secondly, the projected points are triangularized completely. Then topological relations are reverted from the projected points to the in-situ points. At last, a triangular mesh model of the goaf is constructed. In order to effectively implement the algorithm, many methods are studied such as the spherical projection parameters setting, XYZ-orientation cell grid points searching strategy, triangle generation rules, boundary segment strategy by advantage vertexes, boundary closure strategy, and irregular triangle optimization strategy. Applications show that the algorithm can generate a high quality triangular mesh model and provide technical support for accurate 3D modeling and visualized management of a goaf.
Abstract: In order to accurately simulate the whole process of rock creep and explore the generation and development of mircofractures from the meso-level,a visco-elastoplastic Nishihara rheological constitutive model is developed in the two-dimensional particle flow code(PFC2D). Then a non-stationary Nishihara model including two non-stationary elements is put forward in this article. A constitutive equation and a creep equation are derived based on the non-stationary Nishihara model. The user-defined Nishihara constitutive model is called in PFC2D,and a numerical sample whose strength properties are the same as those of a real rock specimen is acquired by parameter testing. Using the data of uniaxial creep tests in laboratory,the non-stationary parameters are back analyzed in Matlab. At last,uniaxial creep tests are simulated using the stationary and non-stationary models,and micro-fractures are monitored.A comparison of these results show that the stationary model can only be used to describe the decay and steady stages,while the nonstationary model is also applicable to the accelerated stage,and thus can simulate the whole process of rock creep. Accelerated creep results from the accelerated development of mirco-fractures and leads to shear failure.
Abstract: Considering the broken rock zone support,tangential and radial stress component analytical solutions of each layer in full contact conditions are deduced in a deep circular tunnel based on the elastoplastic theory. Then an optimization objective function of circular concrete lining layers with different elastic moduli is constructed by choosing different failure criteria and different stress states of concrete and rock materials and by introducing the idea of functionally graded materials,that is,when the objective function is minimum,the most reasonable design is that the Ⅰ,Ⅱ and Ⅲ layer structures destroy at the same time. Finally,the elastic modulus and thickness of the lining is designed separately. The analysis of examples shows the following.(1) With the increase of surrounding rock stress,E2/E1 and E2/E3 both decrease. Under the same stress,there is always E2/E1E2/E3,therefore it is suggested that the elastic modulus of the Ⅰ layer should be greater than the broken rock zone supporting's.(2) With the increase of surrounding rock stress,the thickness of the Ⅰ layer increases. Under the same stress,when E2/E1E2/E3,the thickness of the Ⅰ layer is always less than that obtained when E2/E1E2/E3,therefore the thicknesses of the Ⅰ and Ⅱ layers can be adjusted by changing the elastic moduli of the Ⅰ layer and the broken rock zone support.
Abstract: With the south slope(footwall) of an open pit in Zambia as a research subject,the Rosenbluth point estimation method(PEM) coupled with the jointed finite element method(JFEM) was applied to this jointed rock slope stability evaluation. A probability model was established,which puts the mean and standard deviation of rock material strength parameters(friction angle and cohesive) as input variables and the safety factors as output variables,and the point estimation state functions were solved by the jointed finite element method. According to on-site joints and structural surface surveys,a jointed slope model was built to solve the safety factors,and then the probability distribution of the safety factors was obtained. The results of probability analysis are consistent with the instability situation on site. Since the uncertainty of rock materials and the properties of rock joints are taken into account,this method fully reflects the role of the non-linear relationship among rock layers and makes the rock slope stability estimation more reasonable.
Abstract: The density functional theory(DFT) was applied to investigate the geometric and electronic structures of a series of xanthogen formates. According to the Klopman's generalized perturbation theory,the relationship between the flotation performance of collectors and quantum chemical parameters was analyzed by using the energy and shape of frontier orbitals,natural bond orbital charge,electronegativity,and hardness index. The results show that the bonding atom of xanthogen formates is the S atom in the C=S bond. These parameters such as the energy of the highest occupied molecular orbital(EHOMO),natural bond orbital charge and electronegativity can only infer the flotation activity of collectors. The selectivity of xanthogen formates is mainly related to that copper atoms on the chalcopyritesurface donate d-orbital electrons to the lowest unoccupied molecular orbital(LUMO) and second lowest unoccupied molecular orbital(LUMO + 1) of collectors and then resultin the formation of a back donation covalent π-bond,thus improving the flotation power for chalcopyrite and the selectivity against pyrite. The energies of LUMO and LUMO + 1 can be used to interpret the selectivity of xanthogen formates.
Abstract: On the basis of studies on material flow and energy flow balances in ferronickel smelting,the utilization rate and heat loss of every process were obtained,and the reaction rates of ores,reductants and fluxes were calculated in each part of the ferronickel smelting process. The effect of nickel content in the nickel laterite ore and ferronickel alloy on the contents of nickel and iron in the slag was analyzed. Computational models of overall material flow and energy flow were built. In addition to the function of calculating overall material flow and energy flow in the system,the computational models also have the function of coordinating material flow and energy flow among subsystems. Based on the relevance of material flow and energy flow in each subsystem,the utilization rate and heat loss of flue gas and furnace gas were calculated,and the calculation software of the overall ferronickel smelting process was developed by using Visual Basic.
Abstract: The diffusion couple was used to study solid state reaction in the FexO-TiO2 system at a temperature range of 1323 to 1473 K,during which the oxygen partial pressure was controlled by CO-CO2 gas mixture. The cross-sections of the diffusion couple were observed by electron probe microanalysis(EPMA),and the diffusion concentration profiles of Fe2+,Ti4+,and O2- ions were also determined. In combination with the phase diagram of the Fe O-TiO2 system,it was found that ulvospinel,ilmenite,pseudobrookite phases formed during the reaction and their growth was diffusion-controlled. According to the concentration changes of diffusion ions,the diffusion path of Fe ions was plotted,based on which the solid state reaction mechanism of this system was reasonably proposed.
Abstract: To understand the refinement mechanisms of inclusions in steel,the morphology,size,composition and number of inclusions in low C-Mn steel were characterized by scanning electron microscopy and energy dispersive spectroscopy. The predominance area diagram of deoxidation products was calculated. Some factors which influence the growth of inclusions was discussed. It is found that inclusions in Ti-Mg deoxidized steel are composed of MgO-Al2O3-TiOx,then MnS encapsulated and precipitated on them,isolated Al2O3 and TiOxdo not appear in the steel. The inclusions' morphology is spherical,the average size is about 1.0 μm,and the number is more than 1000 mm-2. Few MgO-Al2O3 and MgO inclusions exist in the steel with high Mg content. Therefore,high Mg content in molten steel is harmful to the control of sphericizing,and it should be restricted to below 50 × 10-6. Magnesium has strong deoxidation ability,and the deoxidation products have the characteristics of small critical radius,large number of nucleation,and the formation of Al-Ti-Mg-O complex inclusions,which both control the supersaturation of oxygen and the growth of inclusions in the steel.
Abstract: The effects of micro Ti and Ti-Mg on the microstructure and impact properties of welding heat affected zones(HAZ)in 16 Mn steel were studied by welding thermal simulation on a Gleeble-1500 hot simulator. The composition of inclusions and the Charpy impact fracture morphologies of the test steels were analyzed by scanning electron microscopy with energy dispersive spectrometry. The microstructures of HAZ in the Ti and Ti-Mg treated steels are mainly grain boundary allotriomorphic ferrite(GBF) + ferrite side plate(FSP) and GBF + intragranular acicular ferrite(IAF),respectively. Inclusions in the HAZ of the Ti-treated steel are TiOx+ MnS with the size of about 5 μm,while inclusions in the HAZ of the Ti-Mg treated steel are Ti-Mg-O + MnS with the size of about 2 μm. The particle size of the latter tested steel is smaller than that of the former one significantly. The HAZ of the Ti-Mg-treated steel has a lot of fine particles which pin cracks and induce the formation of a large number of IAF,leading to that the impact properties of the Ti-Mg-treated steel is better than those of the Ti-treated steel after experiencing large heat input welding.
Abstract: A two dimensional coupled model of fluid flow and heat transfer of liquid steel and water in a mold was established to investigate the influence of inlet cooling water temperature and velocity on the mold tube temperature field and average mold heat flux.Solved by Fluent,this model simulated the flow and heat transfer of liquid steel and cooling water,solidified shell growth,and heat transfer across air gap and mold fluxes by conduction and radiation. The model's accuracy was verified by comparing the shell thickness and copper tube temperature field with other researches. Model results suggest that the inlet cooling water temperature notably affects the cold face temperature of the copper tube. If the inlet cooling water temperature exceeds 313 K,the highest temperature of the cold face will surpass the boiling point of water. However,an increase of 0.49 m·s-1 in water velocity can diminish the adverse effects of an increase of 4 K in inlet cooling water temperature.
Abstract: The microstructures of hot rolled Ti-Mo-bearing low-carbon steel and its precipitation characterization of nano-sized carbides were studied by scanning electron microscopy and transmission electron microscopy. It is shown that precipitation strengthening due to nano-sized carbides is estimated to be approximately 291 MPa. The row spacing of interphase precipitation decreases with the drop of isothermal holding temperature. Though the row spacing of interphase precipitation in ferrite shows a relatively small scatter,it tends to be almost constant against distance from the center of ferrite transformed at different holding temperatures. The observed α/γ interfacial microstructure and interphase precipitation simulation by different theories indicate that this interphase precipitation has a close relationship with the formation of mobile ledges,and the row spacing of interphase precipitation is determined by factors such as ledge height,boundary diffusion coefficient,holding temperature,and ledge velocity.
Abstract: The effect of Nb on the microstructure and mechanical properties of low-alloy wear-resistant steel was analyzed by optical microscopy,scanning electron microscopy,transmission electron microscopy and mechanical property test. By adding 0.034% Nb in low-alloy wear-resistant steel,the hardness increases by HB 9,the Charpy impact energy soars to 37.6J from 29.4J at -20℃ and the anti-wear performance improves by 3.5%. Microstructure refinement and precipitation strengthening are main reasons for the improvement of hardness and impact toughness. Nano-sized particles of Nb C in the Nb-bearing steel precipitate in the process of austenization,pin the austenite grain boundaries and inhibit the growth of austenite grains. This pining type is in accordance with the Zener model,but different from precedent research.
Abstract: Based on the Johnson-Mehl-Avrami type kinetics equations and the Koistinen-Marburger equation,a fully coupled thermomechanical-metallurgical finite element model was established for a door anti-collusion bumper of boron steel 22 Mn B5 in hot stamping. The characteristics of temperature,microstructure and hardness distribution on the door anti-collusion bumper were investigated. The effects of holding force and holding time on the microstructure and mechanical properties of door anti-collusion bumper hot stamped parts were also analyzed. Simulation results indicate that the cooling rate of the top is 137.3℃·s-1 and the cooling rate of the side wall is 69.8℃·s-1. Different cooling rates lead to different microstructure and hardness distributions on the door anti-collusion bumper. With the increasing of holding force,the holding time when the door anti-collusion bumper gets 95% martensite can be shorten,and this can speed up the production efficiency. In addition,we analyzed the microstructure and hardness at the top and side wall of the door anti-collusion bumper. Experimental results show that when the holding time is 10 s,the top and side wall transfer to fully lath martensite,and the hardness at the top is about 508 HV,higher than that at the side wall of 474 HV.
Abstract: High silicon steel with an initial near columnar-grained structure was directly hot-rolled and followed by subsequent warm-rolling,cold-rolling and annealing. Then its microstructure and texture were determined using electron backscatter diffraction,and the magnetic properties of annealed sheets were measured as well. For this high silicon steel,the microstructure and texture evolution of initial near columnar-grained samples represent competitive behavior between fine shear-textured grains near the surface of sheets and coarse grains in the center layer of sheets,which are consisted of α-fiber grains or deformed original cube oriented grains.There are obvious effects of initial columnar grains in the whole process,and a small amount of cube-oriented regions are retained in final annealed sheets,thus the { 111}-fiber texture finally decreases. Furthermore,it is noticed that coarse recrystallized grains are generally related to original cube oriented grains and they are beneficial to the magnetic properties of final annealed sheets. The magnetic properties of annealed sheets in this study are lower than those reported in literature in final sheets with sharp { 120} 〈001〉 or { 001} 〈120〉texture,while they are better than non-oriented high silicon steel. In addition,the difference of magnetic induction between the rolling direction and transverse direction of annealed sheets is small,thus the initial columnar-grained structure is potential to be used in making non-oriented high silicon steel.
Abstract: Fretting test was carried out using an SRV-Ⅳ fretting test rig in order to investigate the fretting behavior and mechanism of Inconel 600 alloy at high temperature. The results indicate that high temperature is beneficial to the formation of an adhesion zone,but restrain the generation of a micro-sliding zone. The friction coefficient and wear loss decrease with the increase of temperature. Friction oxidation mainly occurs in the sliding zone of wear scars,while there is little oxidation in the adhesion zone. Oxygen concentration in the sliding zone at high temperature is more obvious than that at room temperature. At the center of the adhesion region,the oxygen content is low and there is a lot of single Ni,Cr and Fe. At the wear scar surface,the oxides are composed of NiO,Cr2O3 and Fe3O4. At both room temperature and high temperature,microcracks are usually found in the sliding/adhesion junction zone,while the position of crack initiation at high temperature is in the micro-sliding zone. However,the number and length of cracks at high temperature are less than those at room temperature.
Abstract: Paraffin/SiO2 composite phase change materials based on a paraffin core and a silica shell were prepared using TEOS as a silica source through a sol-gel method under acidic condition. Fourier transformation infrared spectroscopy,X-ray diffraction,scanning electron microscopy,differential scanning calorimetry and thermogravimetry were employed to investigate the morphology,chemical structure,crystalloid phase,phase change properties and thermal stability of the composite materials. The results show that the paraffin/SiO2 materials have core/shell morphology with a diameter of about 2 μm. When the core/shell mass ratio reaches 2:1,the encapsulated ratio of paraffin is 66.3%,the melting point of the composites is 54.2℃ with a latent heat of 133.8 J·g-1,and the solidifying temperature is 49.5℃ with a latent heat of 127.5 J·g-1. In comparison to traditional composite phase change materials with a polymeric shell,the thermal conductivity of the paraffin/SiO2 materials increases due to the extra silica shell. This advantage expands applications in building materials and textile fabrics.
Abstract: In the area of internal inclusion detection using ultrasonic,identifying the location and type of internal inclusions using the collected back echo signals has always been a difficult problem. A two-dimensional metallic plate containing inclusions is established. Ultrasonic wave fields inside this material are calculated by the finite element method. Echo waves for two typical inclusions of Al2O3 and TiN and for these inclusions with different depths are obtained. The influences of the type and depth of inclusions on the time-domain and the spectral distribution of interfacial waves,echo waves of inclusions and bottom echo waves are analyzed especially.
Abstract: Internal oil in a hydropneumatic suspension is treated as a research object in recent thermodynamic studies; in fact,there should be a temperature gradient in the oil,and this may result in inaccurate predictions of the temperature change of the suspension. This paper outlines a method of dividing the internal oil into multiple regions to solve the problem. Firstly,a validation experiment was performed to test the temperature gradient in the oil. Then,a lumped parameter thermal model was established to describe the suspension used in the test. The most important is that mass transfer between the regions was taken into consideration in the model. Experimental results show that the temperature gradient exists in the internal oil. In other words,it is inaccurate to make the whole internal oil as a research object. Meanwhile,comparative results show that the proposed model can describe the temperature change regularity of the oil more accurately.
Abstract: A trajectory tracking problem is investigated for wheeled mobile robots with control input constraints and external disturbances. Firstly,the trajectory tracking posture error model is transformed into a T-S fuzzy model. Under this framework and parallel distributed compensation,a design method of constrained H∞ controllers is developed via the piecewise fuzzy Lyapunov function approach,and the stability conditions of the closed-loop system are also derived. Finally,simulation results are given to illustrate the effectiveness of the proposed method.
Abstract: As hand-dorsa vein identification is non-contact,not easily polluted,and has other unique advantages,it becomes a new research and application hotspot of biometric identification methods. The focus of this paper is how to extract hand-dorsa vein image characteristics with high identification rate and robustness. This paper briefly describes the basic principle of local binary pattern(LBP) and improved LBP methods,and analyzes the disadvantages of these methods. A novel method called multi-scale block centersymmetric LBP(MB-CSLBP) is proposed. It includes not only the image's microstructures but also macrostructures,which can give more information of the image. This method is tested on a database of 2040 near-infrared hand-dorsa vein images using MB-CSLBP features and a nearest neighbor classifier. A large number of experimental results show that the proposed method offers a better recognition result of 98.21%,outperforming the original LBP and improved LBP operators,such as CS-LBP and MB-LBP.
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
