Rotor Lorentz force as a parameter for the estimation of vortex flows in a DC electric arc furnace with different bottom electrode positions

This article is devoted to researching a simple parameter which can predict the electrovortex flow in a liquid conductor under a Lorentz force. This is provided by a numerical simulation of the electrovortex and convection flows in a DC electric arc furnace with the bottom electrode in different positions. The electromagnetic, temperature and hydrodynamic distribution parameters are given. It is shown that lifting the bottom electrode above the fettle surface by the electrode radius leads to the decrease of shear stress on the fettle area by 30%, while putting the bottom electrode lower than the fettle surface by a distance equal to the electrode radius and its expansion by the same distance reduces stress by 10%. A good correlation between the shear stress on the fettle area and a rotor Lorentz force provide possibility to use rotor Lorentz force as a simple electromagnetic parameter for the estimation of the vortex flow influence on the increased wearing of the fettle.     

高炉出铁过程中铁水非稳态流动对炉缸炉底侵蚀的影响

基于有效容积为1 750m3的高炉炉缸在实际生产过程中受损状况,利用Fluent软件VOF方法建立高炉炉缸出铁过程的非稳态数学模型,探究铁水流动对炉缸侵蚀的影响。结果表明,死料柱沉底时底部压力较大;剪应力在出铁口的底部、炉缸炉底与死料柱边缘的交线处较大。死料柱浮起时底部所受压力比沉底小,炉底中心的压力较小,而边缘位置则出现负压,剪应力在炉底中心、出铁口的底部等位置较大。无论死料柱沉底与否,出铁口附近的炉壁剪应力在垂直方向上距离出铁口越近则越大,而且出铁口下侧的剪应力高于上侧的剪应力。     

转炉超音速氧枪喷头磨损后的吹炼特性变化

 转炉氧枪喷头会随枪龄的增加发生不同程度的侵蚀,为了探究氧枪喷头侵蚀程度对超音速气体射流吹炼特性的影响,建立了120 t转炉及超音速氧枪的三维全尺寸几何模型,研究了氧枪喷头不同磨损角度对气体射流特性、熔池速度及壁面侵蚀的影响。发现随着磨损角度增加,射流速度衰减加快,射流核心区长度缩短,同一等速线长度缩短,射流中心最大速度和最大速度点距中心距离增大。射流动压衰减速度随磨损角度增加而加快,磨损角度由0增至20°,距喷头端面1.5 m处最大动压减小了14.84%,14 000 Pa等压线包围面积由0.038 m2减小至0.002 m2。钢液面处高速区面积随着磨损角度增加而减小,死区面积随着磨损角度增加而增大。熔池纵截面高速区域主要分布在冲击凹坑和底吹元件附近,低速区域主要分布在熔池底部,死区主要分布在熔池底部中心和炉壁下部区域。当熔池深度小于0.6 m时,顶吹气流对熔池的搅拌起主要作用,磨损角度增加,熔池搅拌能力变弱,熔池横截面高速区面积减小,低速区和死区面积增大;当熔池深度大于0.6 m时,底吹气流对熔池搅拌起主要作用,高速区面积基本不变。渣-金作用区域和底吹流股附近流体湍动能较大、壁面剪切应力较为集中,该部位耐火材料侵蚀严重。熔池壁面附近流体湍动能和壁面剪切力随磨损角度增加而降低,转炉炉衬侵蚀速度减小。     

Characteristics of a Three-Dimensional Square Jet in the Vicinity of a Free Surface

The characteristics of a turbulent jet issuing from a square cross section nozzle in the vicinity of a free surface are presented. Two-component laser Doppler measurements were obtained at eight stations downstream of the nozzle exit, up to a distance of 27 nozzle widths. The Reynolds number based on the exit condition was 40,000. The proximity of the free surface influence the turbulence levels in the jet. Both confinement effects and axis switching influence the evolution of the velocity profiles downstream of the nozzle. The shear stress profiles indicate the formation of a wider mixing zone in the bottom portion of the jet in regions closer to the nozzle exit. Through quadrant decomposition, ejection, and entraining type events were identified. The magnitudes of the peak shear stress in the various quadrants indicate differences in the turbulence characteristics on the top and bottom portions of the jet. As distinguished in the extreme event plots, there are differences in the magnitudes of the peaks and also in their locations.     

Orientation dependence of β1 → β1′ stress-induced martensitic transformation in a Cu-AI-Ni alloy

A systematic investigation was carried out to settle some critical issues on the orientation dependence of the stress-induced martensitic transformation. The transformation we picked up is the β_l (DO3) → β₁′ (18R) stress-induced transformation in a Cu-14.1 mass pct Al-3.9 mass pct Ni alloy. By utilizing tensile tests and two surface analyses coupled with X-ray diffraction, the following clear results were obtained. Concerning the variant selection rule under stress, it was found to be the shape strain which interacts with an applied stress. The critical resolved shear stress for the martensitic transformation was found to have orientation dependence, the shear stress increasing with the normal stress. The observed transformation strains were consistent with those calculated from the shape strain in all orientations. The strong orientation dependence of the Young’s modulus was consistent with that predicted by the elastic constants in the parent phase.     

On the development of constitutive relations for metallic powders

This article describes the development of elastic and plastic constitutive relations as functions of relative density for partially consolidated —100 mesh aluminum powder. First, measurements of yield stress as a function of stress state and relative density are described. Measurements of the plastic strain increments associated with yielding in unconstrained compression tests and elastic properties, both as functions of relative density, are also described. The experimental results are combined with the associated flow rule to show that the yield surface is asymmetric with respect to hydrostatic tension and compression. Second, it is shown that the yield stress results can be represented by a two-part (capped Drucker-Prager) yield surface. The consoli-dation yield surface moves along the hydrostatic stress axis during densification, while the shear yield surface approaches the Mises yield surface. For the Al powder used in the present inves-tigation, superposition of shear stress on a hydrostatic stress state aids the densification process. However, the hydrostatic stress requirement was found to be reduced by only about 20 pct for relative densities below 0. 98. Formerly with the Department of Materials Science Formerly with the Department of Materials Science     

加档坝后高炉炉缸内剪应力对侵蚀的影响

炉缸内铁水流动产生的剪应力对炉缸内衬的侵蚀有重要影响。为此,以流体力学有关理论为基础,建立了炉缸炉底三维流体数学模型,应用CFX软件,研究了不同时期的炉缸剪应力的变化;由于铁水环流对炉缸的侧壁以及炉缸侧壁与炉底交界部位的冲刷作用较强,因此在炉缸侧壁和炉底位置修砌一道环形档坝,观察其对炉底剪应力的影响。结果表明,炉底出铁口近端受到的剪应力较大,而在出铁口远端炉底剪切应力最小;炉底剪应力随着死铁层深度的增大而减小;增加档坝可以有效地减轻炉底受到的剪应力,炉底剪应力越大,增加档坝后减轻的炉底受到的剪应力值越大。     

Bed Drag Coefficient Variability under Wind Waves in a Tidal Estuary

In this paper we report the results of a study of the variation of shear stress and the bottom drag coefficient CD with sea state and currents at a shallow site in San Francisco Bay. We compare shear stresses calculated from turbulent velocity measurements with the model of Styles and Glenn reported in 2000. Although this model was formulated to predict shear stress under ocean swell on the continental shelf, results from our experiments show that it accurately predicts these bottom stress under wind waves in an estuary. Higher up in the water column, the steady wind-driven boundary layer at the free surface overlaps with the steady bottom boundary layer. By calculating the wind stress at the surface and assuming a linear variation of shear between the bed and surface, however, the model can be extended to predict water column shear stresses that agree well with data. Despite the fidelity of the model, an examination of the observed stresses deduced using different wave–turbulence decomposition schemes suggests that wave–turbulence interactions are important, enhancing turbulent shear stresses at wave frequencies.     

Cast microstructure and fatigue behavior of a grain-refined Mg−Zn−Zr alloy

Microstructure studies were conducted on grain-refined Mg-5.1 pct Zn-0.6 pct Zr alloy plates, sand-cast and end-chilled. Grains in this alloy are spherical, nondendritic and increase in diameter with distance from the chill. Coring in these, grains is spherical. The volume fraction of interspherical nonequilibrium secondary phase decreases with distance from the chill, whereas the volume fraction of microporosity increases. Solution kinetics of the secondary phase were found to depend on the dimensionless parameterDt/a ², where:D is the diffusivity of zinc in this alloy,a the sphere radius andt the solutionizing time. The fatigue strength of this alloy at room temperature was measured in reversed bending at a stress level of 10,000 psi and was found to decrease with increasing distance from the chill, both in the as-cast and the cast-and-solutionized conditions. Solutionizing was found to increase fatigue life. Fatigue cracks were found to initiate in shear bands, most frequently at micropores, and to propagate transgranularly.     

Transformation plasticity in iron-nickel alloys

Plastic flow during the austenite ? martensite transformation under constant load has been studied in two Fe?Ni alloys (15.4 pct Ni; 32.9 pct Ni). Transformation plasticity, characterized by the typical linear relationship between the transformation strain per cycle and the externally applied stress,i.e., a quasiviscous behavior, was observed for both alloys. The plastic transformation strain on heating was larger than that on cooling for the 15.4 pct Ni alloy and equal to that on cooling for the 32.9 pct Ni alloy. Transformation plasticity results for both alloys are in quantitative agreement with the pseudo-creep theory of Greenwood and Johnson except for the martensite to austenite transformation in the 32.9 pct Ni alloy where the result is an order of magnitude too low. A dislocation model is proposed which considers the superposition of the large shear stresses generated by the martensite plate formation and the externally applied stress. The model quantitatively predicts the stress dependence of the transformation strain per cycle for transformation plasticity.     

An investigation of strengthening by spherical coherent G. P. Zones

Increases in the critical resolved shear stress of Al-Zn single crystals were measured at 77°C as a function of the volume fraction and average size of the Guinier-Preston (G.P.) zone population. Zone volume fractions ranging from 1.45 to 13 pct were studied which included average zone sizes of from 8 to 90Å. The G.P. zone sizes were determined by an X-ray small angle scattering technique developed by Harknesset al. The increase in the critical resolved shear stress was shown to be determined by the increased Zn-Al interface created by dislocation shear through the G.P. zone. The surface energy of the coherent boundary between zone and matrix was found to be 320 ergs per sq cm by this approach. Furthermore, a model based on surface creation was shown to be consistent with other general features of the deformation process.     

Gravity segregation of complex intermetallic compounds in liquid aluminum-silicon alloys

Primary crystals of intermetallics that are rich in iron, manganese, and chromium form at temperatures above the liquidus, and because their density is higher than that of liquid alumi-num, they cause gravity segregation in the melt. Segregation may occur either in the mold at slow cooling rates or in the bulk liquid in furnaces or ladles. The kinetics of settling of these intermetallic compounds in a melt of Al-12.5 pct Si having 1.2 pct Fe, 0.3 pct Mn, and 0.1 pct Cr has been studied. Sedimentation was investigated at 630 ‡C for settling times of 30, 90, and 180 minutes in an electric resistance furnace. The effect of settling time and height of melt on the volume percent, number, and size of intermetallic compounds was studied by image anal-ysis. The volume percent of intermetallics increases with distance from the melt surface. Both the number of particles and the average size increase during sedimentation. The rate of settling varies with position in the melt due to depletion of intermetallics near the surface and an increase near the bottom. The settling velocities obtained experimentally were compared with terminal velocities calculated by Stokes’ law. Good agreement was generally found. The settling speed of intermetallics reaches the terminal velocity at very short times and very close to the liquid surface. Stokes’ law is therefore applicable to virtually all locations within the melt.     

Laboratory extrusion of Nb3Sn

A study of laboratory direct extrusion of HIP processed Nb₃Sn has been undertaken to assess the effect of hydrostatic pressure on the ductile fracture process that is observed in simple compression above 1400 °C. (Remanent porosity and low melting point microconstituents provide fracture centers; and void growth, linkage, and gross fracture can proceed rather rapidly, with pore linkage being obvious at the specimen surface after a 15 pct reduction in simple compression.) A rather porous, 1200 °C HIP processed material (5 pct porosity and 2.4 pct of low melting point phases) has been successfully extruded at 1650 °C in round bar form to a 51 pct area reduction with neither extensive pore linkage nor gross fracture. The results imply that little porosity development occurs in the presence of hydrostatic pressure of about twice the flow stress. Moreover, in the absence of free surface conditions, effective strains of the order of 0.7 will produce no more than about 10 pct porosity development under hydrostatic pressures of about one-half of the flow stress. Gross porosity development is associated with free surface deformation. Powdered graphite proves to be a poor lubricant, with the bulk of the extrusion pressure reflecting sticking friction.     

Bed-Shear Stress in Turbulent Wave-Current Boundary Layers

An approach for calculating turbulent flows in a wave-current boundary layer over a slowly varying bed is presented. Waves are periodic in time with several harmonics. In this paper, we adopt a time invariant eddy viscosity model, in which the eddy viscosity is linearly proportional to the distance from the bed. The boundary-layer flow field is solved analytically in terms of Fourier components. The approach allows fast computations and can be easily included in a phase resolving wave propagation model. As a part of the results, bottom shear stress and the spatial variation of the boundary layer thickness are also obtained. Present results compare well with experimental data and can explain the asymmetries in the bottom shear stress under sawtooth shaped waves.     

Relationship between tensile and shear strengths of the mushy zone in solidifying aluminum alloys

Strength development in the mushy zone during solidification of three aluminum alloys (Al-4 wt pct Cu, Al-7 wt pct Si-1 wt pct Cu, and Al-7 wt pct Si-4 wt pct Cu) has been measured with two different techniques—horizontal tensile testing and direct shear cell testing. The strength results from the two methods correspond with one another to a much higher degree than suggested by the results presented in the literature. Tensile strength starts to develop at the maximum packing solid fraction, confirmed by the shear strength measurements. The maximum packing fraction represents the point where the internal network structure of the mushy zone is established and ligaments of the network must be broken to rearrange the dendrites. The data indicate a converging trend of the shear and tensile strength at high solid fractions, therefore indicating that the deformation mechanisms are also becoming similar. The results presented in this article suggest that it is possible to develop constitutive equations for the mechanical properties of the mushy zone over the entire solid fraction regime, i.e., from coherency to complete solidification. These equations could be used for the prediction of stress development as well as defect formation.     

Determination of Nonlinear Softening Behavior at FRP Composite/Concrete Interface

For concrete beams and slabs, the bonding of fiber reinforced plastic (FRP) plates to the bottom surface is an effective and efficient technique for flexural strengthening. Failure of strengthened members often occurs due to stress concentrations at the FRP/concrete interface. For debonding failure initiated at the bottom of shear or shear/flexural cracks in the concrete, experimental results clearly indicate a progressive failure process accompanied by gradual reduction in shear transfer capability at the interface. Several existing models for FRP debonding have taken interfacial shear softening into account. However, the assumed shear stress versus slip relations employed in the models have never been properly measured. In this investigation, a combined experimental/theoretical approach for the extraction of interfacial stress versus slip relation is developed. With loading applied to a bonded FRP plate, strain is measured at various points along its length. Based on the strain measurements, the interfacial softening curve is derived from a finite element analysis. The present paper will present the proposed approach in detail, demonstrate its application to typical experimental data, and discuss the implications of the results.     

多层煤-岩介质中扇形深孔爆破应力场特性

在大量现场实验基础上选择有代表意义的实际工程为背景,利用三维数值模拟方法,建立了较合理的煤-岩介质穿层爆破计算模型,获得不同位置抽放孔有效应力随时间的变化规律,分别探讨了各特定位置有效应力随距离增加而衰减的差异.计算结果表明:在计算模型条件下,复合介质孔口煤层和孔底煤层中爆破击穿范围分别为1.4和1.8 m;孔底由于受应力波的叠加和反射双重作用影响,在相同距离时孔底有效应力平均值较孔口大73%;煤-岩复合介质中煤层爆破效果优于单煤层爆破效果,在同等情况下,复合介质煤层中孔口处有效应力极值较单煤层增加17%～42%,孔底增加6%～24%.      

Microstructure and crystallographic texture of strip-cast and hot-rolled austenitic stainless steel

The microstructure and texture of a strip-cast as well as a hot-rolled austenitic stainless steel (18 pct Cr, 8.5 pct Ni) are investigated by the use of optical metallography and quantitative X-ray texture analysis. In the hot band, a homogeneous microstructure is revealed together with a through-thickness texture gradient consisting of a weak cold rolling type of texture in the center layer and a shear texture close to the surface layers. The result is discussed in terms of the through-thickness shear profile that is generated during hot rolling. In the strip-cast material, a random orientation distribution as well as the development of martensite close to the center layer is attributed to the impingement and deformation of the films that are solidified on the surfaces of the casting rolls. The texture close to the surface is attributed to the growth selection of {001}〈uvw〉 oriented grains.     

Deformation Processing Maps for Control of Microstructure in Al-Cu-Mg Alloys Microalloyed with Sn

High-temperature deformation behaviors of Al-5.9?pct Cu-0.5?pct Mg alloy and Al-5.9?pct Cu-0.5?pct Mg alloy containing 0.06?wt pct Sn were studied by hot compression tests conducted at different temperatures and strain rates. Trace content of Sn resulted in a significant increase of flow stress at various processing conditions. Artificial neural network (ANN) modeling was carried out providing excellent prediction of flow stress at different combinations of strain, strain rate, and temperature. It was possible to predict 100 and 89?pct of the flow stress values of the respective alloys within an error less than ±10?pct. The generated flow stress data were used to develop processing maps to delineate the process domains for safe metal working. The power dissipation efficiency maps revealed a maximum efficiency of 60 and 40?pct, respectively, for the base alloy and the microalloyed material. The instability maps generated for the Sn containing alloy revealed only one instability regime. The safe processing zone of the investigated alloys primarily lies at lower regimes of strain rate, which is extended up to higher deformation temperatures, with trace addition of Sn. Optical microscopy characterized these stable regions as dynamic recrystallization (DRX), which resulted in considerable flow softening observed at a low strain rate of 0.001 s^?1. Instability was observed mainly due to shear band formation or intercrystalline cracking.