Abstract: The interaction process between particles and bubbles can be classified as collision, attachment, and detachment; all three sub-processes determine the collection probability between particles and bubbles. Upon collision, the hydrophobic particles strongly attach to the rising air bubbles, which carry them to the surface, thereby overflowing the flotation cell in the collecting launder. Hydrophilic particles unattached to the rising air bubbles are left to settle at the bottom of the cell to be discharged. Whether the target mineral particles can attach to the rising air bubbles is the key to froth flotation. Therefore, studying bubble-particle attachment to improve the flotation efficiency is quite significant. The bubble-particle attachment probability model, EDLVO theory, force analysis of the bubble-particle aggregate, influence factors, and experimental progress of the bubble-particle attachment were systematically analyzed. Based on the methods of contact time, induction time, and energy barrier, the adhesion probability model was analyzed from the perspectives of dynamics and thermodynamics, and the effect of particle size, bubble size, particle hydrophobicity, particle surface roughness, and pH values on adhesion probability were explained. The force analysis of the bubble-particle aggregate under quiescent and turbulent conditions was conducted. Typically, there exist three types of attachment forces of the bubble-particle aggregate:capillary force, hydrostatic pressure force, and buoyancy force. The weight force is the only detachment force of the bubble-particle aggregate in the quiescent condition, but the vibration and centrifugal forces are also detachment forces in the turbulent condition. Many researchers have conducted substantial research on particle-bubble adhesion using advanced instruments and detection means, and have made several research achievements. However, because bubble-particle interaction is extremely complicated, the interaction conditions are simplified during experimental study. Therefore, the attachment process is not satisfactorily described by the available theory. Combined with practical application demands, a bubble-particle study should be conducted from a deeper and more comprehensive level.
Abstract: There are various interfacial phenomenona in ironmaking and steelmaking, including slag foaming, nucleation, aggregation, removal of inclusions in steel, and refractory corrosion. The slag-metal interface has a crucial influence on the mass transfer, energy transfer, and interfacial chemical reaction. Interfacial wettability is a very important aspect of the interfacial interaction, and studying it is essential to further understand the interfacial phenomenona. In general, the interfacial wettability can be measured by contact angle and interfacial tension. In studying interfacial phenomena, it is necessary to first measure various quantities of interfacial wettability such as surface tension, interfacial tension, and contact angle, on the same conditions of interfacial phenomena or processes. Improving the interfacial wettability can be beneficial to the control of melting and refining processes. For example, when the contact angle between the molten slag and inclusion in steel reduces and the surface tension of the molten slag increases, the adhesion between the molten slag and inclusion is stronger, and it becomes easier to remove the inclusions. Therefore, the basic concepts of contact angle and interfacial tension were first introduced in this paper. Furthermore, the common methods of measuring contact angle and surface tension in an elevated temperature system were summarized, especially for the sessile drop method, which is the mostly used in laboratory experiments. During steelmaking processes, the interfacial wettability is significantly influenced by the system compositions, especially the surface active elements in steel and the surface active composition in slag. Moreover, the influences of temperature are also considerable. Hence, the effects of these two main factors, compositions and temperature, on the interfacial wettability were analyzed in detail. Finally, the wettability among the common materials in steelmaking processes was summarized.
Abstract: Metals with a high strength-to-weight ratio are being increasingly used in the automobile industry to achieve a reasonable tradeoff between weight reduction, crashworthiness, fuel efficiency, and environmental friendliness. However, sheets of lightweight metals such as advanced high strength steel, aluminum alloy, magnesium alloy, and titanium alloy, tend to crack without obvious necking during widely-used stamping processes. In particular, so-called shear-induced ductile fracture, which occurs near the pure shear loading path, exceeds the prediction spectrum of traditional necking-based forming limit curves. In addition, the single point incremental forming (SPIF) process, which is currently under rapid development because of its high flexibility in rapid prototyping or customized production process, demonstrates a strong necking suppression. Consequently, ductile fracture without distinct necking has been considered as the forming limit for SPIF. Although the classical forming limit prediction approach, which is, in principle, based on necking instability, has been widely applied as a standard solution for predicting failures in the process of sheet-metal forming, it barely provides feasible solutions to the aforementioned issues. This limitation greatly restricts the application of lightweight materials and the development of novel forming processes. Therefore, researchers have devoted increasing attention to accurately predicting the ductile fracture of metallic materials. In the current paper, we first review studies related to the micro-mechanisms that trigger ductile fracture. We then systematically review ductile fracture prediction models in two categories:coupled models and uncoupled models. Model applications in metal forming processes are summarized as well. Toward the conclusion, prospective trends in ductile fracture research are surveyed. The objective of this paper is to provide engineers and researchers with a beneficial overview of the selection, utilization, and development of ductile fracture prediction models.
Abstract: Tungsten smelting slag is an important secondary resource, it contains tungsten, tin, tantalum, niobium, scandium, and other useful metals, which have great recycling value. However, tungsten smelting slag is a solid waste that can cause groundwater and soil pollution. Further, the progress of the comprehensive recovery and utilization of tungsten smelting slag was reviewed. The process of wolframite and scheelite smelting, the recovery process theories of tin, tantalum, niobium, and scandium, and the reduction of tungsten smelting slag were also presented. Tungsten and tin can be recovered by gravity separation and flotation, which is followed by smelting. This process is easy in case of industrial applications, and the cost is low, however the adaptability is poor, and fine materials cannot be effectively recycled. Tungsten, tin, tantalum, niobium, and scandium can be recovered by hydrometallurgy, which is a complex process that considerably influences the environment. Tungsten smelting reduction is a fundamental requirement for the comprehensive utilization of slag, which is mainly used to manufacture the cement materials, porous materials, and microcrystalline glass.This study introduced the current research status, identifies problems, and provides suggestions for future research. The bottleneck of scandium, tantalum, and niobium extractions depends on the development of an extractant and ion exchange resin. The first principle and chemical coordination theory from the field of materials and chemistry can be used to solve the problem, including poor selectivity of extractant, low exchange capacity of ion exchange resin and large quantity of waste water. Strong selective extractant and ion exchange resin with high exchange capacity will be studied to solve above problems. The interaction mechanism is investigated based on the atomic level, and the efficient extraction agent and ion exchange resin are selected. Future research may be related to the development of a green extraction technology and a short process to produce slag from high value materials.
Abstract: To investigate the damage mechanism of tunnel portal subjected to gas explosion in the Luodaiguzhen tunnel, equivalent and quantitative studies were carried out on the accumulation of gases in the tunnel, and a fully coupled numerical model with dimensions that were consistent with the actual dimensions was established by LS-DYNA and verified. The RHT model was used to simulate the concrete, and some parameters were modified. The propagation traits and strength of the blast shock wave and the damage mechanism of the tunnel portal were studied. The studies show that the strength of the shock wave is significantly enhanced due to its numerous irregular reflection. This results in a complicated wave field. The wave aggregates in local regions, and the pressure in the tunnel is 1.2-2.4 MPa. The wave near the lining travels faster during propagation, and its shape changes from the spherical to horn. The strength of the wave in the vault of the tunnel portal is increased by 56% to reach 2.8 MPa, and diffraction occurs in the vicinity of tunnel portal. After the wave is propagated from the tunnel, its strength gradually decreases, and the wave, which originally moves along the sidewall and floor, continues to travel along the longitudinal direction. The shock wave along the arch moves upward and forms a "mushroom cloud". The corner of the sidewall is destroyed completely during the explosion, and the lining suffers serious damage within 7 m of detonation, and the arch is almost intact in the range of 7-15 m. The tunnel portal is also severely damage. Without the constraint of surrounding rock, the displacement of the vault in the Y and X directions of the portal is 0.26 and 0.14 m, respectively, and the tensile stresses that acted at the front and back surfaces of the portal are 7.9-31.5 MPa and 4.9-15.6 MPa, respectively, and multiple peak stresses occur on the back surface of the portal. The damage of the portal is mainly caused by the tensile stress. By comparison, the numerical simulation results of the damage characteristics of the tunnel portal basically agreed with the actual situations. Therefore, the results can provide useful references for the treatment of lining hazards.
Abstract: The charge structure is an important aspect of deep-hole cumulative blasting, and its influence on the blasting effect cannot be ignored; a reasonable charge structure can improve the rate of explosive energy utilization, thereby improving the blasting effect. In the study of the mechanism of deep-hole cumulative blasting in coal seam, the concentric decoupled charge structure is extensively analyzed. However, in the field test, the centers of the explosive charge and blast hole are offset because of the effect of gravity. Moreover, an eccentric decoupled charge structure is formed, which changes the decoupling coefficient around the blast hole and affects the blasting effect. This study focuses on the influence of the charge structure on improving coal seam permeability. The influence of the charge structure on the propagation characteristics of the explosion-induced stress wave and the partition of the explosion fracture was analyzed. A field experiment on coal seam deep-hole cumulative blasting was designed based on the gas geological conditions of the Ji group seam in Pingdingshan Coal Mine. Additionally, the influence of the charge structure on the horizontal and vertical directions of coal seam was discussed. Experimental results of deep-hole cumulative blasting in coal seam indicate that the charge structure has an influence on coal seam permeability. In the horizontal blasting area, the average increase in gas concentration is 52.78% after blasting. In the inspection holes located above and below the blast hole respectively, at a vertical distence of 1 m, after blasting, no blasting smoke escapes from the hole above the blast hole, but the blasting smoke escapes from the hole below the blast hole, which proves that the influence of the eccentric decoupled charge structure on coal seam below the blast hole is greater than that on coal seam above it. Moreover, the range of the fracture above the blast hole is smaller than that below the blast hole.
Abstract: The electrochemical behavior of the chalcocite oxidation process in the presence and absence of microorganisms was investigated using electrochemical techniques, including cyclic voltammetry, anodic polarization curves, Tafel curves, and X-ray photoelectron spectroscopy (XPS) analysis. The research results prove the stepwise dissolution mechanism of chalcocite in the presence and absence of microorganisms. The initial stage of oxidation is initiated at low redox potentials. During the initial stage, the intermediate products of CuxS (1 ≤ x < 2) are successively oxidized until CuS is formed. The later stage is the oxidation of the intermediate product CuS and this period requires initiation at high redox potentials owing to the formation of a passivation layer on the electrode surface, and the reaction rate of the later stage is extremely slow; in this case, it is the rate-limiting step of the whole reaction. The cyclic voltammograms show that the electric current density in the presence of microorganisms is higher than that in the absence of microorganisms, indicating that the microorganisms accelerates the dissolution rate of chalcocite. The anodic polarization curves show that the pitting potential of chalcocite is low; the potential range of the first active corrosion zone in the presence of microorganisms is much wider than that in the absence of microorganisms, indicating that the intermediate products of the sulfur film are passivating, and their effects could be reduced by the oxidation of microorganisms; in this manner, the dissolution rate of chalcocite is promoted. To identify the components of the passivation layer during the process of chalcocite dissolution in the presence and absence of microorganisms, the electrodes were detected via XPS. The XPS analysis results show that the components of the passivation layer on the electrode surface are complex, including CuS, polysulfide (Sn2-), elemental sulfur (S0) and intermediate oxidation products that contain sulfate (SO42-) and that CuS is the main passivating component; therefore, the oxidation of chalcocite follows the multisulfur method.
Abstract: Ultrafine bainitic steels, which are derived from nanostructured carbide-free bainitic steels, exhibit a remarkable combination of ultra-high strength and toughness together with excellent wear resistance. Their excellent integrated mechanical properties has made ultrafine bainitic steels a popular choice for application as wear-resistant parts. In this study, a 0.7-C low alloy ultrafine bainitic steel was designed, and the effects of different austempering temperatures on the bainitic transformation kinetics, microstructure, and dry sliding wear resistance of ultrafine bainitic steels were studied. Dilatometry, two-body abrasion testing, optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction, laser-scanning confocal microscopy, and energy-dispersive spectrometry were used to study the abovementioned effects. Meanwhile, the wear performance and wear mechanism under two-body abrasion of ultrafine baintic steels with different austempering temperatures were also studied. The results demonstrate that the microstructures of ultrafine bainitic steel produced at different austempering temperatures comprise both lamellar bainitic ferrite and film-like and blocky retained austenite. With increasing austempering temperature, the transformation rate of bainite increases, and the incubation period and phase transformation completion time of bainite significantly reduce; in addition, the bainitic ferrite plates are more coarsened, the volume fraction of retained austenite increases, and the hardness decreases. Moreover, when the ultrafine bainitic steel is subjected to the twobody abrasion test, the wear surface is mainly featured by furrows and grooves, and the predominant wear mechanism is micro-cutting. Furthermore, the wear resistance of ultrafine bainite post austempering at different temperatures is better than that of tempered martensite; this wear resistance increases with decreasing isothermal temperatures. Ultrafine baintic steel post austempering at 250℃ possesses the best wear resistance, and the relative wear resistance is 1.28 times higher than that of tempered martensitic steel; this is attributed to the refined microstructure and the transformation induced plasticity (TRIP) effect of ultrafine bainitic steel.
Abstract: Compared with other types of aluminum alloys, A7085 aluminum alloy has a series of excellent properties such as high strength, high toughness, and high fatigue resistance. These advantages meet the requirements of aircraft performance; thus, A7085 aluminum alloy is widely used for fabricating aircraft components. The shell cracks in aeronautical structures are often mixed-mode cracks, i. e., comprising open type and sliding type, and they are also known as the Ⅰ-Ⅱ compound crack. It has been found that fatigue fracture is the main reason for the failure of most specimens. At present, most studies on fatigue crack are focused on mode Ⅰ crack, but the load on the specimen is usually not a single pure type Ⅰ, Ⅱ, or Ⅲ mode. It is usually a combination of these three kinds of loads. When the crack is subjected to Ⅰ-Ⅱ mixed-mode loads, its crack growth rate and crack growth path are affected by the loading conditions. To investigate the mechanism of Ⅰ-Ⅱ mixed-mode fatigue crack growth of A7085 under different loading angles, mixed-mode (Ⅰ-Ⅱ) fatigue crack growth tests were performed on compact tension shear (CTS) specimens using a servo-hydraulic fatigue testing machine. The stress intensity factor of the crack tip was calculated by finite element analysis. Furthermore, C and m in the Paris law were calculated using seven-point incremental polynomial methods. The results show that when under different loading angles, cracks will extend along the vertical direction of the external load. Moreover, the path seems to be a straight line. The results of experiments agree with the maximum tensile stress theory. Once the crack expands, type Ⅱ stress intensity factor KⅡ basical-ly remains at 0, while type Ⅰ stress intensity factor KⅠ increases gradually. The stress intensity factor amplitude is almost equal to K Ⅰ, and crack propagation is mainly controlled by KⅠ. The result is helpful to understand the mechanism of the Ⅰ-Ⅱ fatigue crack propagation.
Abstract: Beryllium is one of the most important materials in particle physics and nuclear physics experiments. Among these applications, it is used as the material in particle collision tubes, such as the beam pipe in the operational Beijing Electron and Positron Collider (BEPC Ⅱ) and in the Circular Electron Positron Collider (CEPC) currently in the planning stage. High-speed particles produce large amounts of γ irradiation and impose a heat load on the beam pipe. The beam pipe must be cooled by the scouring fluid to maintain a stable temperature for particle detection; this cooling process will induce fluid erosion of the beam pipe. The corrosion properties of materials in contact with the oil No. 1 for electric discharge machining (EDM-1) fluid under irradiation are not yet known. A device for testing pipeline corrosion was built to study the corrosion of beryllium in EDM-1 fluid after γ pre-irradiation. The mass of the sample was measured by an electronic balance, and the surface morphologies and composition were examined by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The results show that the corrosion of beryllium in EDM-1 is affected by two corrosion mechanisms:erosion and chemical corrosion. Erosion is mainly influenced by the surface morphology of the sample, whereas the chemical corrosion is mainly influenced by the dose of γ irradiation, impurity elements in the sample, and organic sulfides in EDM-1. Measurements of the sample before and after irradiation reveal that the mass decreases, then increases, and then decreases again under the combined effects of the two kinds of corrosion. The corrosion rate increases substantially with increasing radiation dose, and γ pre-irradiation promotes pitting nucleation and the formation of pitting holes in beryllium in EDM-1. After 2880 h of corrosion, the sample not subjected to pre-irradiation exhibits only obvious pitting nuclei, whereas some of the pitting nuclei on the sample subjected to 200 and 100 kGy of pre-irradiation develop pitting holes; the diameter of the pitting holes in the former case is approximately twice that of the pitting holes in the latter case. The larger the radiation dose, the earlier the pitting occurs and the larger the diameter of the corrosion holes. Impurity elements (e. g., Al, Si, Fe, Cr, and Ti) and S appear in the pitting nuclei and pitting holes. The impurity elements in the beryllium samples are important factors to induce pitting. The chemical reactions of organo-sulfur compounds produce SO2 and SOx(SO2, SO3, and SO4) in the pitting holes by physical and chemical adsorption, which promotes the formation and expansion of pitting.
Abstract: For weld defects such as holes, debasement of the joint properties and large deformations easily appear in fusion welding of the AA7B04 aluminum alloy, and the use of mechanical connections such as riveting increases the weight of the connector. Herein, a 2-mm AA7B04 aluminum alloy was friction stir welded using an industrial KUKA Titan Robot, with a friction stir welding end effector mounted onto the robot. The Fx, Fy, and Fz forces of the tool during welding were recorded, and the resultant mechanical strength and microstructure of the joints were studied. The results show that welding speed imposes a great influence on Fz. The microstructure and mechanical properties at different welding speeds of a friction stir welded joint of an AA7B04 aluminum alloy sheet were investigated via optical microscope observation, transmission electron microscope observation, a tensile test, a three-point bending test, and a hardness test. The results show that the maximum tensile strength of the joint is 447 MPa for a welding speed of 100 mm·min-1, equivalent to 80% of the parent metal. No crack is observed in the joints when bending at 180°. W-shape hardness distribution is observed on the cross-section of all joints; moreover, owing to the lowest hardness in the heat affected zone and the junction of the welding area, different welding speeds lead to different welding thermal cycles, and the hardness of joint increases with the increase in the welding speed. Dynamic recrystallization occurs in the nugget zone, and fine equiaxial grains are produced. The grains of the advancing and retreating sides of the thermo-mechanically affected zone are obviously deformed. The η' phase can be observed in the heat affected zone of the advancing side, and η' phase particles can also be observed in the heat affected zone of the retreating side. Owing to the higher temperature, the larger η phase can also be found in the heat affected zone of the retreating side.
Abstract: The power load of the smart grid fluctuates increasingly high and rapidly because of the introduction of intermittent energy, such as wind energy and solar energy. As a result, the increase of the randomly fluctuating load in the smart grid brings new challenges to the active power measurement of smart electricity meters. However, the installed power meter and the standard electricity meter are designed for a steady input signal. The traditional MA (moving average) and ⅡR (infinite impulse response) measurement algorithms are proposed for the steady situation and are thus not suitable to address the dynamic error testing and metering problems. Moreover, although some harmonic experiments have been performed that provide an overview of domestic and internal standards of electricity energy meter, there is a lack dynamic characteristics in them. Thus, it is of great theoretical significance and application value to study the dynamic measurement characteristics of the existing smart electricity meters and propose an effective dynamic measurement to improve the metering dynamic performance. To reduce the measurement error of a smart electricity meter under dynamic load power conditions, a SDPA algorithm for dynamic active energy measurement was proposed in this work. First, the dynamic response speed and dynamic error characteristics of active power of traditional MA and ⅡR low pass filter algorithm were deduced. Next, the limitations of the two algorithms for dynamic input signal were highlighted, and the influence factors were determined by theoretical analysis. Based on these results, a SDPA algorithm for dynamic measurement of smart electricity meter was proposed. The new algorithm was implemented by truncating periodically, executing piecewise point product operation and summing up the active power. In addition, the implementation method by decimation can save storage space and improve the operation speed. The theoretical and simulation results show that the SDPA algorithm can reach a lower error level in one period of response time.
Abstract: Because of the increasingly rigid and complex operating conditions for multi-stage pumps, the annular seal is playing an important role in determining the dynamic characteristics of a rotor system. The annular seal can prevent fluid leakage to ensure that the pump system can satisfy the design requirements, such as the head and efficiency. However, the fluid-induced force that is caused inside the annular seal by the pressure reduction and nonconcentric motion directly acted on the rotor system, which presents transient characteristics with a variation in the operating conditions. Based on the Euler angle transformation and the finite element method, the differential equations of motions for impeller and shaft were determined in this study, and the coupled effects, including the fluid-induced force of the annular seal and multiple axial forces, were considered. These equations of motions and coupled effects were conducted to investigate the effect of the annular seal on the lateral-axial bi-direction coupled vibration for a multi-stage pump rotor system. Finally, the lateral-axial bi-direction coupled vibration model for a multi-stage pump wet rotor was integrated with the matrix operation,and the corresponding coupled transient dynamics were solved using the Newmark method. The changing rules of the coupled vibration characteristics and fluid-induced force were mainly investigated for different sealing lengths, pressure drops, and clearances. The calculated results imply that the influence of the annular seal on the Lomakin effect for rotor lateral vibration becomes increasingly obvious with increasing length and pressure drop and with decreasing clearance. The convergence rate for the lateral vibration is observed to be faster than that for the axial vibration, and the vibration frequencies for the lateral-axial bi-direction presents different features. Furthermore, the fluid-induced force between the sealing lengths presents a nonlinear relation, whereas that between the pressure drop and clearance exhibits a linear relation.
Abstract: The need for straighter bar products continues to increase with the development of production automation technologies and increasing user requirements, and bar manufacturers have set higher requirements for the bar finishing process. The two-roll straightening machine has become the key equipment of the bar finishing line, and its process directly relates to the quality of the final product. The traditional bar straightening technology is based on the theory of primary bending of bars, and by controlling the degree of plastic deformation, the straightening process of bars can be roughly established, but this is not suitable for high-precision straightening. In this study, to obtain the variation law of each curvature in the cross-roll straightening process of bars, a one-time bendingspring calculation model of the bar was realized by applying the spring back theory of small curvature plane bending and the bendingspring back curvature equation. Based on the principle of bending once per half rotation and by considering the residual curvature of the last bending as the original curvature of the next bending, the bending-spring model of the whole two-bar straightening process was established. The evolution of the original curvature, bending curvature, spring curvature, and residual curvature of the whole straightening process were obtained, and then the final residual curvature of the bar was obtained. The theoretical model was used to calculate the production process, and the results are consistent with the field results, which verifies the correctness of the theoretical model. Based on the established theoretical model, the straightening process was analyzed under different diameters, different material yield strengths, and different original deflections, and the deformation law of straightening process under different incoming parameters was obtained. The model can provide a theoretical basis for the optimization design and process parameter calculation of the two-roll straightening machine.
Abstract: The propellers of an aerostat are prone to both amplitude and rate saturations during the movement of the aerostat, thus affecting the stability and movement of the system. Generally, the conventional method of processing saturation can only handle the amplitude saturation of the system input, and the rate saturation problem is usually converted to an amplitude saturation problem, so it is a complex process. Therefore, it is worthwhile to study the control method that can simultaneously deal with amplitude and rate saturations. Some anti-windup compensator design methods can only be applied to linear systems, and some nonlinear anti-windup control methods for nonlinear systems require much online calculations to obtain the control law, which is not conducive to real-time control. Therefore, a novel control method was applied to the nonlinear research object. The nested saturation function could realize the bounded amplitude and differential of the input when used as a control law because of its specific form. Thus, it could be used to solve the amplitude and rate saturation problems in an aerostat system. This paper presented the design of an anti-windup controller for a nonlinear multi-propeller aerostat with amplitude and rate saturations of control input. First, the three-DOF model of the aerostat was established and transformed into two chain-like integral systems by taking forces other than propeller thrust as disturbances. Based on the theory of nested saturation control, the relationship between the amplitude and rate saturations of control inputs and the parameters of saturation function was obtained. Taking the aerostat as the research object, decoupled controller for longitudinal and lateral channels was designed to realize the bounded amplitude and rate of the system input. The global stability of the system was proved by the Lyapunov stability theorem, and the dynamic performance of the system was analyzed under different adjustable parameters. Considering the wind disturbance, the effectiveness and robustness of the controller was verified by simulations.
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
