Abstract: A series of Brazilian split tests on rock-cement interface considering the effect of interface orientations were conducted to investigate the influence of hard rock-soft rock interface direction on failure behavior. The tensile strength for different interface orientations was obtained and failure mechanism of the interface was analyzed by the particle flow code PFC2D. The measured tensile strength increases as the interface-loading angle increases. The measured tensile strength can be considered to be equivalent to that of the interface if the interface orientation is parallel to the loading direction, because tensile failures occur along the interface. Mixedmode failures occur if the interface is not parallel to the loading line. In addition, another series of Brazilian tests were conducted to investigate the influence of the interface tensile strength on failures by increasing the cement dosage and roughening the rock surface. Based on the results, a diagram of the failure mode distribution marked with the typical failure patterns from the Brazilian test results for the rock-cement interface was developed. These findings provide a better understanding of the failure modes of the hard rock-soft rock interface.
Abstract: The preparation of cementitious materials for filling primarily via the alkali-activated method was discussed to recycle copper slags. A mixture of lime, NaOH, and early-strength agent was selected as a composite activator to carry out copper slag activation and filling material-preparation experiments, and the hydration products were analyzed by X-ray diffraction and scanning electron microscopy. The test results show that the effect of different activators on sample strength follows the order lime > early-strength agent > NaOH. The strengths of slag paste samples at 7 and 28 d post-curing reach 1.5 and 3.0 MPa, respectively. The strength of filling materials mixed by copper slag and tailings is 1.0 MPa as the curing ages are 28 d, and the slurry has well fluidity. These values meet the requirements of a suitable filling material. The early hydration products of copper slag mainly include Ca(OH)2 and C-S-H gel. As the curing time increases, the Ca/Si ratio of the C-S-H gel decreases and the structure of the hydration products becomes more compact. After curing for 28 d, the active components in the copper slag are nearly completely reacted.
Abstract: To improve the thickening efficiency of tailings in sand bins and achieve a high-concentration sand discharge, the sound field as a research method was introduced, and the characteristics of sound-field radiation to transmit the non-contact sound field was innovatively used to tailings slurry. Tailings slurry with 40% in mass fraction was prepared for the experiment. After 15, 20, 25, 30, 35, and 40 min of sedimentation, an ultrasonic wave of 20 kHz and 50 W of power were applied to investigate the effect of ultrasonic waves on the final settling time and concentration with different settling times. Ultrasonic wave was also applied to the sand discharge stage, and the rheological parameters of the tailings slurry at different concentrations were measured. The results show that when an ultrasonic wave is applied after 20 min of sedimentation, the shortest slurry sedimentation time of 80 min can be obtained and the final sediment mass fraction of the tailings slurry can reach 77.5%. Therefore, under ultrasonic action, it is possible to achieve stable sand discharge with a high-concentration tailings slurry at the same time, and the discharge mass fraction up to 74.04%. Comparisons of the viscosity and yield stress of the tailings slurry before and after ultrasonic treatment indicate that the viscosity of the slurry can be effectively reduced by 22.3% by ultrasonic action, which is a good viscosity reduction effect. Ultrasonic vibration, cavitation, and the acoustic streaming effect are the reasons for the rapidly thickening sedimentation and discharge of the tailings slurry.
Abstract: Agglomeration technology is one of the most effective measures to enhance the poor heap permeability of ores caused by the presence of fine particles. Selecting the proper acid resistant binder is key to the successful heap leaching of copper ore. The agglomeration of oxide-sulfide mixed copper ore was studied in this paper, and results show that Biometek-WLAG001 is an ideal acid resistant binder. The effects of binder amount, water spray amount, rotational speed, curing time, aging acid addition amount, and aging time on the compressive and wet strengths of agglomerated pellets were investigated in single-factor experiments. The effects of binder amount, curing time, aging acid addition amount, and aging time on the wet strength of agglomerated pellet were further studied via a response surface methodology, and results were optimized and analyzed by Design-Expert 8.0 software. The interaction mechanism between the binder and the ore was investigated by Fourier transform infrared spectroscopy analysis and Zeta potential measurements. Results reveal that the binder and ore undergo chemical adsorption but not electrostatic attraction.
Abstract: An experiment was conducted to determine the difference between using biomass pine sawdust and pulverized coal in the reduction roasting of high-iron Bayer process red mud from the perspective of reduction temperature, reduction time, and reducing agent dosage. Experimental results show that biomass pine sawdust reduction roasting is quicker, occurs at a lower temperature, and is a superior process to pulverized coal reduction roasting. The mechanism of using biomass pine sawdust in reduction roasting of high-iron Bayer process red mud at a low temperature was investigated using thermal analysis, X-ray diffraction, and dynamic analysis. In addition, the optimum conditions involved in reducing high-iron Bayer process red mud were determined using biomass pine sawdust at medium and low temperatures. It is found that when using 20% biomass pine sawdust in mass at a reduction temperature of 650℃ and a reduction time of 30 min, the high-iron red mud in the Bayer process can be completely magnetized. A thermogravimetric experiment conducted on biomass pine sawdust indicates that the main stage of sawdust pyrolysis occurs within a temperature range of 250-375℃. The pyrolysis rate reaches a maximum at about 350℃, but tends to be gentle at 450℃. The main stage of pulverized coal pyrolysis occurs at 300-700℃; the pyrolysis rate is at its maximum at 450℃ but it tends to be gentle at 650℃. The kinetic study shows that at a temperature of 300-400℃, the apparent pyrolysis activation energy of the sawdust is much lower than that of pulverized coal, indicating that sawdust is more prone to pyrolysis than pulverized coal at this temperature range. In summary, biomass reduces high-iron Bayer red mud at a lower temperature, which is about 200℃ lower than that of coal-based reduction.
Abstract: Using the ultra-heavy-plate jet-impingement quenching test device and the multi-channel temperature recorder, 84 mm large section plates quenching temperature drop curve was experimentally investigated under the condition of jet velocities ranging from 3.39 to 26.8 m·s-1, Reynolds number from 12808 to 117340 and jet densities ranging from 978.7 to 6751.5 L·(m2·min)-1. Then, wall heat flux, heat transfer coefficient and boiling curve were calculated with inverse heat transfer modified method. The results indicate that both jet velocity and jet density influence the plate surface heat transfer mechanism and the distribution of the maximum heat flux. When jet velocity is low, a mixed heat transfer and "heat flux shoulder" phenomenon can be observed in wall parallel flow zone. With increased jet velocity, the film boiling heat transfer mechanism disappears and the maximum heat flux changes to the low-wall superheat position. These research results benefit the calculation of the temperature field and the control of structure property during ultra-heavy plate quenching.
Abstract: By applying ultrasonication during direct chill casting, a 2219 ingot with a diameter of 1250 mm was successfully produced. To study ultrasonic inner mechanism of ingot, the microstructure and macrosegregation of ingots cast after ultrasonication were analyzed by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and direct-reading spectrometry. The results show that the cavitation and acoustic streaming effects brought by ultrasonic vibration can obviously regulate the structure and refine the grain size of the resulting ingots. The central grain refinement rate observed is 39.6%. Ultrasonication promotes the formation of branched intergranular secondary phases with a discontinuous distribution, and transgranular precipitates present a dispersed distribution with dot. Ultrasonication also effectively decreases negative segregation near the surface of the ingots, reduces the difference solute concentration between their edge and center, and weakens fluctuations in concentration over the entire cross section of the samples, thereby improving the macrosegregation properties of the final products.
Abstract: The effects of temperature and Cl-and dissolved oxygen (DO) concentrations on the electrochemical corrosion behaviors of 316L stainless steel used in pressurized water reactor primary pipes were investigated via a composite design strategy, potentiodynamic polarization and electrochemical impedance spectroscopy measurements, and oxide film morphology observation. The results reveal that temperature is the most significant factor affecting the corrosion behavior of the steel:the higher the temperature, the higher the corrosion current density and the lower the pitting potential of the steel. The effects of Cl-and dissolved oxygen concentrations are highly related to the temperature. When the temperature is relatively low (T < 150℃), relationships between the Cl-and dissolved oxygen concentrations and corrosion current density of the steel are hardly observed, although the pitting potential decreases with increasing Cl-concentration and decreasing dissolved oxygen concentration. As the temperature increases, the dependence of pitting potential on the Cl-and dissolved oxygen concentrations disappears (at T > 130℃ and T > 150℃, respectively), and the corrosion current density increases with increasing Cl-and dissolved oxygen concentrations. The electrochemical impedance spectroscopy (EIS) measurements and oxide film observations further confirmed these experimental results.
Abstract: To understand the reasons behind edge cracks of large-scale cast ingot during hot deformation, this paper compared the compositions, phase ratios at different temperatures, and differences in the hardness of two phases in the middle and edges of cast ingots. The microstructure and fracture morphology of the samples were observed by optical microscopy, scanning electron microscopy, and electron back-scattered diffraction. The results indicate the presence of smaller grains and larger ferrite content in the edge portion than in the middle. However, edge cracking is also more serious than middle cracking, which indicates that grain size and phase proportion are not the main factors influencing the side cracking of ingots. Compared with that of the middle portion, the hardness difference between the two phases of the ingot edge is larger. Thus, the strain distribution of the two phases varies during hot deformation, and stress concentration occurs along the phase boundary. More precipitates are observed in the phase boundary of the ingot edge than in that of the middle specimens, and these precipitates are believed to destroy the continuity of the matrix, leading to microcracks.
Abstract: Because of the low cost, easy preparation, and good temperature stability, Fe-based amorphous alloys with excellent mechanical properties, magnetic properties, and corrosion resistance have been widely studied. Fe-based amorphous alloys can be used as anti-irradiation materials since their inherent disordered structure helps to resist the damage caused by irradiation. Thus, irradiation can be used to test the performance of these alloys and optimize their structure. The progress of research on the irradiation properties of Fe-based amorphous alloys is summarized in this article, which focuses on the study of neutrons, ions, and electron irradiation performance. The relationships between different amorphous alloy components and the type, energy, fluence of irradiated particles, structure, and properties of the alloys are discussed, and the crystallization mechanism induced by irradiation is evaluated. The results obtained can provide a valuable reference for promoting the development of Fe-based amorphous alloys.
Abstract: The process of electroless copper plating in an EDTA/THPED dual-ligand system using sodium 3,3'-dithiodipropane sulfonate (SPS) as an additive was studied by the electrochemical method. The mixed potential of the system was measured as a function of time, and results indicate that addition of SPS gradually shifts the mixed potential toward the negative direction without saltation. The dual-ligand electroless copper system was then tested by linear sweep voltammetry, and SPS is found to accelerate both cathodic and anodic polarization. The additive mainly influences the anodic polarization of the formaldehyde oxidation process and the rate of copper deposition is improved to a certain extent. The surface morphology and texture of the resulting plated copper were also analyzed by scanning electron microscope, energy dispersive spectrometer and X-ray diffraction, and a high-purity product without Cu2O inclusions is confirmed. Moreover, the X-ray diffraction results of the electroless copper layers show that addition of SPS favors the formation of the preferred orientation on the (200) lattice plane.
Abstract: The equivalent stiffness of the egg-box structure was investigated to achieve structural optimization of the structure parameters. A unit cell of the egg-box structure was studied using the variational asymptotic method to obtain a numerical calculation method for equivalent stiffness of the whole egg-box structure. This numerical calculation method was then used to analyze the equivalent stiffness of the egg-box structure with different structural parameters. A formula for equivalent stiffness characteristics was then fitted, and the structural parameters were treated as independent variables. Finally, the fitted formula was used to optimize the dimensionless structural parameters to obtain maximum buckling load and maximum energy absorbed per unit weight when Poisson's ratio or equivalent stiffness was restricted. Results show that the tensile stiffness of the egg-box structure is reduced, but the bending stiffness is increased. In addition, there is a nonlinear relationship between stiffness and structural parameters, and the structure exhibits a negative Poisson's ratio. Furthermore, active parameters optimization design of the egg-box structure can be easily achieved with the fitted formula.
Abstract: The long-term performance of overlap adhesion, one of the major joint technologies of FRP, is key to its practical engineering application. Experiments on the creep behaviors of the double lap joint of a hybrid FRP (HFRP) were conducted. Obvious creeps were observed and measured under various environments reflecting different levels of shear stress and humidity. Then, a fractional derivative rheological model was proposed to characterize the creep deformation of the overlap joints. By applying the Mittag-Leffler function to the proposed model, an improved Powell optimization algorithm with an initial-value calculation method was utilized to determine the values of the fitting parameters on the basis of the experimental data obtained. By introducing stress influence functions to the conventional fractional calculus, a modified formula of fractional creep compliance was considered to reflect the influence of stress level on the creep property of the overlap joint. Results indicate that the model is capable of predicting the creep behavior of overlap joints up to a sustained stress level of 30%-70% of the shear strength with relative simple mathematical expressions and only a few fitting parameters.
Abstract: To ensure the integrity, real-time performance, confidentiality and usability of data transmission in networked control systems and improve the ability of the system against data attacks, a data transmission strategy based on the MD5 hash code, time stamp, and AES encryption algorithm was proposed. This strategy takes into account the security and real-time of data transmission of both the controlled object side and the controller side of the networked control system. And the networked predictive control based on round trip time delay was used to compensate for the effect on the system after it had been attacked by data, so that the system can be stably controlled after being attacked by some intensity of data and also achieves a better control effect, thereby improving the ability of network control systems to deal with attacks. The S100-1 training platform pipeline pressure control system is used to prove that the proposed networked predictive control system based on the secure transmission strategy has better security and anti-attack ability.
Abstract: A representative hardware-in-the-loop simulation system was established for the mixed separation process to meet the demands of industrial process control technologies with complex characteristics. A hardware-in-the-loop simulation system was developed composed of a virtual object computer, a controller-design computer, a monitoring computer, virtual actuators, virtual detecting instruments, and a control system to achieve mixed separation. The control algorithm of the system was based on actual industrial software, and Matlab was use to design the virtual object, virtual actuators, virtual detecting instruments, and online identification system. The mechanism modeling of controlled object, parameter identification of controller design model, controller design and controller performance evaluation were completed on the virtual object computer, controller-design computer and monitoring computer. The proposed system lays the foundation for future industrial applications of control algorithms for complex industrial processes.
Abstract: Stereoscopic visual fatigue occurs after an individual watches a 3D display for a long period of time, which limits its development. As such, it is necessary to undertake an effective and objective evaluation of stereoscopic visual fatigue. The relative power of three electroencephalography (EEG) wavebands, namely θ (4-8 Hz), α (8-13 Hz), and β (13-22 Hz) and three algorithms, E(α+θ)/β、Eα/β、E(α+θ)/(α+β) were elicited in eight EEG channel regions and in all the channels, respectively. The results show there to be 54 possible EEG indicators available for identifying the optimal indicator for assessing stereoscopic visual fatigue. Lastly, based on the results of a paired-samples t-test, grey relational analysis (GRA), and a support vector machine (SVM), the algorithms parietal Eα/β is proved to be the best indicator. In addition, θ activity remains stable over time, whereas α activity increases significantly (p < 0.01) and β activity decreases significantly (p < 0.01) when in a fatigue status.
Abstract: Tensile testing of HTRB600 steel bars under high temperature was conducted to determine the mechanical properties of the steel under high temperature. The elastic modulus, proportional limit, yield strength, ultimate strength, and stress-strain curves of steel bars at 20, 200, 300, 400, 500, 600, 700, and 800℃ were obtained. The experimental results show that the elastic modulus, proportional limit, yield strength, and ultimate strength of the bars obviously decrease with increasing temperature. The yield strength, ultimate strength, proportional limit, and elastic modulus of the steel bars at 500 and 800℃ decrease to less than 50% and 10%, respectively, of those of the sample at room temperature. The stress-strain curve of the steel bars smoothens as the temperature increases, and the yield terrace disappears at 200℃. The degree of decrease in yield strength and ultimate strength of the 600 MPa steel bar is obviously larger than that of the < 500 MPa steel bar. Finally, a simplified calculation method to determine the stress-strain curve of HTRB600 steel bars under high temperature was proposed.
Abstract: A detailed three-dimensional finite element model including soil-structure interaction was developed for a 1.5 MW onshore wind turbine. A comparative study was performed to investigate the soil-structure interaction (SSI) effects on the seismic responses of the wind turbine under operating conditions. Wind speed time histories were converted to wind load time histories under the operating condition by using the FAST program. Simulation analysis was conducted using the EERA program to derive earthquake excitations at the base of the soil model. Then modal analyses and seismic response analyses were performed. The results show that soil-structure interaction has significant influences on the dynamic characteristics of the wind turbine tower, which results in amplification of the structural responses.
Abstract: To determine the effect of fortification intensity on the mechanical properties and amount of material used in reinforced concrete frame-tube structures, high-rise buildings over 100 m in height that were either built or being built were researched. 12 models of high-rise office buildings ranging from 150 m to 300 m in height and with different seismic intensities were analyzed, with respect to their period ratios, shear-weight ratios, stiffness-weight ratios, earthquake and wind-load influences, and the costs of steel and concrete for different fortification intensities. The results show that for the Jinan International Finance Center Landmark Tower, with increasing fortification intensity, the natural vibration period of the structure decreases, the torsion period lags behind the vibration period, the torsional effect reduces, and the shear-weight ratio significantly increases. Structures with low fortification intensities are greatly influenced by gravity as a second-order effect and their entire stability becomes the main safety control factor. The influence of earthquake action increases with increased fortification intensity. In the region with seismic fortification intensity 6 (0.05 g), steel consumption for buildings over 200 m in height increases significantly and in the intensity region 8 (0.20 g), steel consumption has linear growth with height. The concrete dosage in unit area in intensity region 6 (0.05 g) is close to that in intensity region 7 (0.10 g), and increases by about 19% in intensity region 8 (0.20 g). As such, the influence of fortification intensity is significant with respect to structural material dosage.
Abstract: Using the Hermite moment model, three types of wind fields with different probability characteristics, namely the Gaussian, hardening non-Gaussian, and softening non-Gaussian processes, were generated via the Kaimal spectrum for a typical wind turbine under operational conditions. Reliability analysis of the fatigue life of the wind turbine was performed by taking tower base connections as an example with consideration of the joint probability density distribution of the wind direction and mean wind speed. The dynamic response was calculated by an aerodynamic model of the blade and multi-body dynamics, and the time-and frequency-domain characteristics of the response were analyzed. Using linear damage accumulation theory and the Paris equation, the fatigue crack initiation life and crack growth life of the turbine were discussed in detail. Fatigue estimation shows that the crack initiation life of the turbine is more sensitive to non-Gaussian winds, whereas its crack propagation life is less sensitive to the non-Gaussian characteristics of wind load. The influence of the non-Gaussian characteristics of wind load on the fatigue damage of the wind turbine should be considered. In terms of the full-direction inflow, the failure positions of the crack initiation and propagation stages are identical and in the dominant wind direction.
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
