Mg−6Al−2Sr alloys with different Sm contents (0%, 0.5%, 1%, 1.5%, 2%, mass fraction) were prepared by melting and casting method. The effects of Sm on the microstructure and mechanical properties of as-cast Mg−6Al−2Sr alloys were studied by optical microscope, scanning electron microscope, energy dispersive spectrometer, transmission electron microscope, X-ray diffraction and tensile test. The results show that the microstructure of as-cast Mg−6Al−2Sr alloy is composed of α-Mg, Mg₁₇Al₁₂, Mg₁₃Al₃Sr and lamellar acicular Al₄Sr phase. After adding Sm element, granular block Al₂Sm phase appears in the grain. With the increase of Sm content, the discontinuous long strip reticular Mg₁₇Al₁₂ phase and the lamellar acicular Al₄Sr phase gradually decrease, and the Al₂Sm phase increases and distributes more dispersedly, so the alloy microstructure is continuously refined. The average grain size of the alloys decreases at first and then increases with the increase of Sm content. When the Sm content is 1.5 wt%, the average grain size reaches the minimum value of 94.6 µm. With the increase of Sm content, the mechanical properties of the alloy at room temperature first increase and then decrease. When the Sm content is 1.5 wt%, the alloy has the best comprehensive mechanical properties at room temperature.

As the next generation biomedical titanium alloy, β-type titanium alloys are excellent candidates for biomedical applications due to the relative low elastic modulus and the contained non-toxic elements. However, the relative low strength and unsatisfactory tribological property are undesired for load-bearing implant applications. In this study, 0–5 at% Si was added to the classic Ti−35Nb−5Ta−7Zr alloy to improve its strength and wear resistance, and the (Ti−35Nb−5Ta−7Zr)_1−x−Si_x (x=0, 1 at% and 5 at%) alloy were fabricated by selective electron beam melting (SEBM) technology. The results indicated that Si addition significantly increases in compressive yield strength, which is mainly due to grain refinement strengthening. At the same time, the wear rate of the as-built TNTZ-5Si alloy in SBF solution was only ∼30% of the Ti−6Al−4V alloy. Consequently, the TNTZ-5Si alloy showed an excellent combination of compressive yield strength, elastic modulus and wear resistance for potential load-bearing implant applications.

The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffraction and electron probe microanalyzer to examine the distribution of oxides and the features of hole defects, and using ABAQUS 3D thermo-mechanical coupling finite element model based on arbitrary Lagrangian-Eulerian method to simulate the material flow behavior. Oxides exist at the edge of tunnel hole and in the micropores in the joint. Based on distribution of oxygen and material flow behavior, it is believed that the oxides on the surface of the alloy tend to flow down into the bulk along the flow direction of plastic material during friction stir welding, aggregate in the weak region of material flow at the intersection of the shoulder affected zone and the stir pin-tip affected zone, and consequently prevent the material from contacting and diffusing. Due to the insufficient material flow and therefore the small plastic deformation, the pressure is not high enough to compress the accumulated oxides, resulting in hole defects.

The adsorption mechanism of O-isopropyl-S- [2- (hydroxyimino) propyl] dithiocarbonate ester (IPXPO) to chalcopyrite was investigated by using contact angle, in-situ atomic force microscopy (in-situ AFM), cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The results of contact angle and in-situ AFM demonstrated that IPXPO adsorbed on chalcopyrite increases surface hydrophobicity and roughness. It was found by CV experiments that a layer passive film was formed. The results of XPS spectra further revealed that the thiol S atom, oxime N atom, and O atom in the IPXPO molecule might react with copper atoms to form Cu-S, Cu-N, and Cu-O bonds, respectively. An artificial mixed minerals flotation test indicated that under the condition of pH=6.79 and IPXPO initial concentration 5×10⁻⁵ mol/L, the flotation recovery of chalcopyrite reached about 90%, while for pyrite only 25%, suggesting that IPXPO is an excellent collector for flotation separation and enrichment of chalcopyrite.

The role of Fe/S ratios (ω, g/g) in the uranium bioleaching from a complex uranium ore by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans consortium was investigated. The results showed good uranium extraction with over 90% at the Fe/S ratio of 5:0.5, 5:1 and 5:5, while poor extraction (<46%) at the Fe/S ratio of 5:0 and 5:10. Furthermore, the bacterial community analysis based on species-specific gyrB numbers indicated that, absent sulfur or excessive sulfur would be not conducive to the synergistic growth for A. ferrooxidans and A. thiooxidans, and then not conducive to the uranium dissolution. Meanwhile, the sulfur-oxidizers could play an important role in the process of uranium synergistic bioleaching by mixed bacterial consortia. Additionally, the characteristics of mineral residue was detected by SEM-EDS. The results showed appropriate sulfur dosage would change the structure and improve the porosity of passivation substance. Lastly, the uranium dissolution kinetics and biochemical reaction mechanism was analyzed. It indicated that the biochemical reaction coupling iron and sulfur had a pleiotropic effect on the uranium dissolution from the ore particles, appropriate Fe/S ratio is the key factor for uranium bioleaching by chemoautotrophic acidophiles.

Non-precious electro catalysts with high-efficiency, cheapness and stablility are of great significance to replace noble metal electro catalysts in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, triangular Cu@CuO nanorods on Cu nanosheets were fabricated by a novel in-situ oxidation approach using Cu nanosheets as self-template and conductive nano-substrate in an aqueous solution of NaOH/H₂O₂, and then by low-temperature phosphorization treatments. The experimental results show that the phosphating temperature has a significant effect on the morphology, composition and number of active sites of Cu@Cu₃P nanorods. The Cu@Cu₃P-280 electrode exhibits a good HER catalytic activity of achieving a current density of 10 mA/cm² at 252 mV in acid electrolyte. After catalysis for 14 h, the current density can still reach 72% of the initial value. Moreover, the Cu@Cu₃P-280 electrode also shows an excellent OER catalytic activity in basic electrolyte, reaching a current density of 10 mA/cm² at the overpotential value of 200 mV. After catalysis for 12 h, the current density remained more than 93% of the initial value. This work provides a theoretical basis for the directional design and preparation of sustainable, low-cost, bifunctional electrocatalytic materials.

Natural minerals receive growing attention as inexpensive, green, and efficient catalysts for degradation of organic pollutants. Mechanical activation of natural chalcopyrite was conducted for improving the catalytic performance. Tetracycline degradation was evaluated in the presence of hydrogen peroxide and mechanically activated chalcopyrite. Tetracycline degradation at 100 min is 55.52% (Chp10), 68.97% (Chp30), 77.79% (Chp60), and 86.43% (Chp120), respectively, and the rate constant of pseudo-first-order kinetics is 0.0079, 0.0109, 0.0137 and 0.0192 min⁻¹, respectively. Chalcopyrite samples were examined by multiple characterizations. Mechanical activation of natural chalcopyrite induces the decline of particle size and slight increase of surface area, smaller grain size, lattice strain, and partial sulfur oxidation. The relationship between catalytic activity and property change manifests that the improved catalytic ability is mainly ascribed to the increase of surface area and surface oxidation induced by mechanical activation. This work provides novel insights into the improvement of catalytic performance of natural minerals by mechanical activation.

Phosphogypsum (PG), the main by-product of phosphoric acid production industries, is considered one of the most important secondary sources of rare earth elements (REEs). The current study focuses on the recovery of REEs content and the residual phosphate content existing in the PG with preserving on the CaSO₄ skeleton to be used in other various applications. These attainments are carried out using citric acid leaching process via soaking technique. Several dissolution parameters for REEs using citric acid were studied, including soaking time, soaking temperature, citric acid concentration, solid-to-liquid ratio, and recycling of the citrate leaching solutions in the further REEs dissolution experiments. The best-operating conditions were 14 d of soaking time, 7.5% citric acid concentration, and the solid-to-liquid ratio of 1/5 at ambient temperature. About 79.57% dissolution efficiency of REEs was achieved using the optimal conditions. Applying four soaking stages by mixing different fresh PG samples with the same citrate solution sequentially, cumulative dissolution efficiency for REEs was found to be 64.7% under optimal soaking conditions. REEs were recovered using Dowex 50X8 resin from citrate solutions with 96% extraction efficiency. Dissolution kinetics proved the pseudo-first-order nature, reversible reactions, and two activation energies for all REEs.

This article studies the influence of polymers on drag reduction and heat transfer enhancement of a nanofluid past a uniformly heated permeable vertically stretching surface. Our prime focus is on analyzing the possible effects of polymer inclusion in the nanofluid on drag coefficient, Nusselt number and Sherwood number. Dispersion model is considered to study the behavior of fluid flow and heat transfer in the presence of nanoparticles. Molecular approach is opted to explore polymer addition in the base fluid. An extra stress arises in the momentum equation as an outcome of polymer stretching. The governing boundary layer equations are solved numerically. Dependence of physical quantities of engineering interest on different flow parameters is studied. Reduction in drag coefficient, Nusselt number and Sherwood number is noticed because of polymer additives.

The cause and treatment of rail corrugation for the metro have always been a popular and challenging issue. In this work, the field measurements were carried out on rail corrugation, track stiffness, and the track dynamic response. A three-dimensional finite element model was developed to investigate the cause of rail corrugation. The constraints on rail vibration from two wheelsets and adjacent wheel-rail interactions were taken into account in the model. According to experimental and simulation results, the suppression measure for rail corrugation was proposed and the suppression mechanism was discussed. It was found that the cause of rail corrugation is related to vertical and lateral vibration of the rails outside the two wheelsets at around 380 Hz. The increased stiffness of the fasteners reduces the vibration energy of the rail and the wheel-rail force. However, simply increasing the stiffness of the fasteners may not be effective in the suppression of rail corrugation. If necessary, the rails need to be grinded to reduce the roughness to a certain level, so that increasing the fastener stiffness can effectively suppress the rail corrugation.

Optimization of an automotive body structure faces the difficulty of having too many design variables and a too large design search space. A simplified model of body-in-prime (BIP) can solve this difficulty by reducing the number of design variables. In this study, to achieve lighter weight and higher stiffness, the simplified model of BIP was developed and combined with an optimization procedure; consequently, optimal designs of automotive body B-pillar were produced. B-pillar was divided into four quarters and each quarter was modelled by one simplified beam. In the optimization procedure, depth, width, and thickness of the simplified beams were considered as the design variables. Weight, bending and torsional stiffness were also considered as objective functions. The optimization procedure is composed of six stages: designing the experiments, calculating grey relational grade, calculating signal-to noise ratio, finding an optimum design using Taguchi grey relational analysis, performing sensitivity analysis using analysis of variance (ANOVA) and performing non-dominated sorting and multi-criteria decision making. The results show that the width of lower B-pillar has the highest effect (about 55%) and the obtained optimum design point could reduce the weight of B-pillar by about 40% without reducing the BIP stiffness by more than 1.47%.

With the increasing complexity of industrial processes, the high-dimensional industrial data exhibit a strong nonlinearity, bringing considerable challenges to the fault diagnosis of industrial processes. To efficiently extract deep meaningful features that are crucial for fault diagnosis, a sparse Gaussian feature extractor(SGFE) is designed to learn a nonlinear mapping that projects the raw data into the feature space with the fault label dimension. The feature space is described by the one-hot encoding of the fault category label as an orthogonal basis. In this way, the deep sparse Gaussian features related to fault categories can be gradually learned from the raw data by SGFE. In the feature space, the sparse Gaussian (SG) loss function is designed to constrain the distribution of features to multiple sparse multivariate Gaussian distributions. The sparse Gaussian features are linearly separable in the feature space, which is conducive to improving the accuracy of the downstream fault classification task. The feasibility and practical utility of the proposed SGFE are verified by the handwritten digits MNIST benchmark and Tennessee-Eastman (TE) benchmark process, respectively.

The direct torque control of the dual star induction motor (DTC-DSIM) using conventional PI controllers is characterized by unsatisfactory performance, such as high ripples of torque and flux, and sensitivity to parametric variations. Among the most evoked control strategies adopted in this field to overcome these drawbacks presented in classical drive, it is worth mentioning the use of the second order sliding mode control (SOSMC) based on the super twisting algorithm (STA) combined with the fuzzy logic control (FSOSMC). In order to realize the optimal control performance, the FSOSMC parameters are adjusted using an optimization algorithm based on the genetic algorithm (GA). The performances of the envisaged control scheme, called G-FSOSMC, are investigated against G-SOSMC, G-PI and BBO-FSOSMC algorithms. The proposed controller scheme is efficient in reducing the torque and flux ripples, and successfully suppresses chattering. The effects of parametric uncertainties do not affect system performance.

Fluid invasion through fractures is frequently observed in subsurface engineering. To elucidate the microkinetic behavior of fracture fluids, the microfracture structure of coal from the Surat Basin was reconstructed using a 3D morphometric system and stitching algorithm, then the transparent models characterizing the fracture structure were produced using microfluidics, and water invasion in the microfracture model was measured via visualization experiments under various conditions. High flow rate facilitated the invasion of the water phase into the closed channel, improving the efficiency of water invasion in the neutral wetting system. Wettability reversal changed the dominant channel for water invasion in the hydrophobic system. The invasion efficiency in closed and small aperture bypass channels was low. The reduction of effective seepage channels led to the fastest breakthrough time. Higher surface tension and interfacial curvature promoted the hysteresis effect. The reduction of effective seepage channels led to the fastest breakthrough time. The larger surface tension and interfacial curvature make the hysteresis effect more significant. These results will enable a better understanding of the rock-gas-liquid multiphase interaction mechanisms under unsaturated conditions of rocks.

The time-dependent behaviors of coal and rocks were easily ignored. Besides, “three-stage” triaxial loading and unloading mechanics tests of sandstone were conducted based on the idea of the initial high in-situ stress state recovery according to the full-life cycle evolution characteristics of surrounding rocks in deep mines (pre-excavation, excavation and post-excavation). The time-dependent stress — strain curves of sandstone were obtained. Meanwhile, the deformation and strength fitting relationships with time of sandstone were also built. Furthermore, the dilatancy and volumetric recovery mechanical mechanisms of sandstone were revealed. The results showed that: 1) There were significant time-dependent evolution characteristics on the deformation and strength of sandstone; 2) There were significant correlations among the internal friction angle, cohesion and the simulated depths; 3) Volumetric recovery phenomenon of sandstone was observed for the first time, which mainly occurred at the simulated depth of 2000 m. The above research conclusions could provide a certain theoretical basis for the stability control of surrounding rocks in deep mines.

Radon is a polluting and radioactive gas released by rock fracture. Shear fracture is widely developed in surrounding rock mass of deep engineering. Nevertheless, the correlation between radon release and the shear fracture is undefined. In this study, the intact Jinping marble and Baihetan basalt were adopted as samples. Based on radionuclide content analysis, the intrinsic characteristics of radon emission were analyzed. Then a direct shear testing system was designed to synchronously measure radon release during rock fracture. The direct shear tests were carried out under different normal stresses. The relationship between shear fracture process and cumulative radon concentration was explored. The results indicated that radon release varied with the increase of shear displacement under the same normal stress. The general pattern showed a slight increase and fell in the initial loading phase, then increased rapidly to the peak release approximately corresponding to the peak of shear stress, and finally decreased to a stable level with the development of shear displacement after sample failure. The initial and peak radon concentrations increased linearly with the increase of normal stress. The same trend was found in shear failure surface area and cumulative radon concentration according to the rise angle (RA) value-average frequency (AF) distribution.

Rockbursts were frequently encountered in the construction of deeply buried tunnels at the Jinping-II hydropower station, Southwest China. In those cases, the existence of large structural planes, such as faults, was usually observed near the excavation boundaries. The formation mechanism of the “11·28” rockburst, which was a typical rockburst and occurred in a drainage tunnel under a deep burial depth, high in-situ stress state and complex geological conditions, has been difficult to explain. Realistic failure process analysis (RFPA^3D) software was adopted to numerically simulate the whole failure process of the surrounding rock mass around the tunnel subjected to excavation. The spatial distribution of acoustic emission derived from numerical simulation contributed to explaining the mechanical responses of the process. Analyses of the stress, safety reserve coefficient and damage degree were performed to reveal the effect of faults on the formation of rockbursts in the deep tunnel. The existence of faults results in the formation of stress anomaly areas between the tunnel and the fault. The surrounding rock mass failure propagates toward the fault from the initial failure, to different degrees. The relative positions and angles of faults play significant roles in the extent and development of surrounding rock mass failure, respectively. The increase in the lateral stress coefficient leads to the aggravation of the surrounding rock mass damage, especially in the roof and floor of the tunnel. Moreover, as the rock strength-stress ratio increases, the failure mode of the near-fault tunnel gradually changes from the stress-controlled type to the compound-controlled type. These findings were consistent with the microseismic monitoring results and field observations, which was helpful to understand the mechanical behavior of tunnel excavation affected by faults. The achievements of this study can provide some references for analysis of the failure mechanisms of similar deep tunnels.

The deformation of soft rock roadway caused by floor heave is a major challenge for coal mines in China western mining areas. To achieve security and stability of soft rock roadway, this work considered the headgate at panel 11505 of the Yushujing Coal Mine as background. First, based on the limit equilibrium method and slip line field theory, a model of floor heave was established, the mechanism of floor heave control was analyzed, and an optimized support method was proposed. Then, the displacement, stress and failure zones around the surrounding rock with the original and optimized support were studied by FLAC. Finally, the serviceability of the support method was verified by field application. The results showed that the main deformation form of soft rock roadway is floor heave, and 0.5 m is relatively reasonable thicknesses of the inverted arch. The extrusion failure zone and shear failure zone were mainly affected by tensile and shear failure, respectively. The modification of floor and the effective support are key points. The failure zone was consistent between numerical simulation and theoretical calculation. The maximum convergences of floor heave determined by numerical simulation and field measurement were 220 mm and 240 mm, respectively, which were reduced by 55% and 60% compared with the original support, and the convergence between sidewalls decreased considerably. The optimized support method controls the floor heave well.

China’s first high-pressure hydraulically coupled rock-breaking tunnel boring machine (TBM) was designed to overcome the rock breaking problems of TBM in super-hard rock geology, where high-pressure water jet system is configured, including high-flow pump sets, high-pressure rotary joint and high-pressure water jet injection device. In order to investigate the rock breaking performance of high-pressure water-jet-assisted TBM, in situ excavation tests were carried out at the Wan’anxi Water Diversion Project in Longyan, Fujian Province, China, under different water jet pressure and rotational speed. The rock-breaking performance of TBM was analyzed including penetration, cutterhead load, advance rate and field penetration index. The test results show that the adoption of high-pressure water-jet-assisted rock breaking technology can improve the boreability of rock mass, where the TBM penetration increases by 64% under the water jet pressure of 270 MPa. In addition, with the increase of the water jet pressure, the TBM penetration increases and the field penetration index decreases. The auxiliary rock-breaking effect of high-pressure water jet decreases with the increase of cutterhead rotational speed. In the case of the in situ tunneling test parameters of this study, the advance rate is the maximum when the pressure of the high-pressure water jet is 270 MPa and the cutterhead rotational speed is 6 r/min. The technical superiority of high-pressure water-jet-assisted rock breaking technology is highlighted and it provides guidance for the excavation parameter selection of high-pressure hydraulically coupled rock-breaking TBM.

To explore the effects of thermal treatment on cracking processes in granite, granite samples were thermally treated at 25–400 °C and then loaded under uniaxial compression. Active ultrasonic testing and passive acoustic emission (AE) monitoring were combined to monitor the damage characteristics of the samples. The uniaxial compression strength (UCS) of the sample treated at 200 °C shows no apparent change compared with that of the nonheated sample, while the UCS increases at 300 °C and decreases at 400 °C. As the temperature increases from 25 to 400 °C, the initial P-wave velocity (V_p) decreases gradually from 4909 to 3823 m/s, and the initial V_p anisotropy ε increases slightly from 0.03 to 0.09. As the axial stress increases, ε increases rapidly in the crack closure stage and unstable cracking stage. The attenuation of ultrasonic amplitude spectra also shows an obvious anisotropy. Besides, the main location magnitude of AE events decreases after thermal treatment, and low-frequency AE events and high-amplitude AE events increasingly occur. However, there is insufficient evidence that the treatment temperature below 400 °C has a significant effect on the temporal characteristics, source locations, and b-values of AE.

The original version of this article unfortunately contained a mistake. The mistake is corrected as follows:

1) The name of the Foundation item is incorrect. The correct is “Projects(1253929, 1910853) supported by the National Science Foundation”.