Carbon fiber reinforced plastics provide many excellent properties and are widely used in the aerospace industry. However, the existing composites autoclave process still faces difficulties such as high-energy consumption, uneven distribution of temperature field, complications of pressure transmission, and high cost, which limit their application in manufacturing of large complex composites components. In this study, the vibration treatment was introduced into the composites microwave curing process innovatively. On the basis of giving full play to the uniform heating characteristics of the microwave, the problems of a large number of internal defects and poor molding quality caused by the insufficient curing pressure have been solved. The results showed that the samples cured by the improved microwave process without external pressure had a few internal voids, excellent interface bonding conditions, and lower residual stress. Their properties were almost consistent with the samples prepared by the standard autoclave process, which provided a new method for the high-performance, efficient, safe, and low-cost manufacturing of large complex composites components.

Resin matrix carbon brush composites (RMCBCs) are critical materials for high-powered electric tools. However, effectively improving their wear resistance and heat dissipation remains a challenge. RMCBCs prepared with flake graphite powders that were evenly loaded with tungsten copper composite powder (RMCBCs-W@Cu) exhibited a low wear rate of 1.63 mm³/h, exhibiting 48.6% reduction in the wear rate relative to RCMBCs without additives (RMCBCs-0). In addition, RMCBCs-W@Cu achieved a low friction coefficient of 0.243 and low electric spark grade. These findings indicate that tungsten copper composite powders provide particle reinforcement and generate a gradation effect for the epoxy resin (i.e., connecting phase) in RMCBCs, which weakens the wear of RMCBCs caused by fatigue under a cyclic current-carrying wear.

In order to understand the initial surface damage of Al piston in unsteady thermal environment like knock combustion, T6 heat treated cast Al-Si-Cu alloy was thermal shocked under different heating speeds between room temperature and 450 °C by adjusting the environmental temperature. The surface evolution was mainly characterized in view of roughness, hardness, morphology, texture, phase and element distribution. Results indicated that both the roughness and hardness went up to the maximum and then decreased with rising heating speed. Micro-structure and phase analysis suggested that the interactions of solid phase transition and oxidation with enhancing thermal stress took responsible for the surface evolution.

The microstructure evolution of 7A85 aluminum alloy at the conditions of strain rate (0.001 − 1 s⁻¹) and deformation temperature (250–450 °C) was studied by optical microscopy (OM) and electron back scattering diffraction (EBSD). Based on the K-M dislocation density model, a two-stage K-M dislocation density model of 7A85 aluminum alloy was established. The results reveal that dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main mechanisms of microstructure evolution during thermal deformation of 7A85 aluminum alloy. 350–400 °C is the transformation zone from dynamic recovery to dynamic recrystallization. At low temperature (≼350 °C), DRV is the main mechanism, while DRX mostly occurs at high temperature (≽400 °C). At this point, the sensitivity of microstructure evolution to temperature is relatively high. As the temperature increased, the average misorientation angle (

This paper investigates process parameter effects on microstructure and mechanical properties of the tubes processed via recently developed friction assisted tube straining (FATS) method. For this purpose, design of experiment was used to arrange finite element analyses and experimental tests. Numerical and experimental tests were executed by changing rotary speed, feed rate and die angle. Taguchi design results show that increasing feed rate and decreasing rotary speed enhance Zener-Hollomon (Z) parameter and decrease average grain size, while die angle has no considerable effect. Increasing Z value reduces grain size and enhances flow stress of the processed samples, while the experiment with the highest Z value refines initial microstructure from 40 to 8 μm and increases flow stress by 5 times.

The reinforcement corrosion is the pitting corrosion of chloride corrosion. Hence, in this study, the variations of reinforcement tensile strength due to stress concentration of pitting corrosion are analyzed. The stress concentration consequence of corrosion on the reinforcement tensile capacity is studied utilizing tension tests and creating different ABAQUS software models. According to the modelling in various corrosion depths, strength reduction is less than 5% in corrosion with pit radius to reinforcement diameter ratio up to 0.3 and for corrosions higher than 0.4, the measure of capacity reduction is increased more to 30%.

D2EHPA (P204), tri-butyl-phosphate (TBP) and sodium chloride (NaCl) were attractive for selective extraction of scandium from acid leaching solution of red mud. The extraction parameters of P204 concentration (X_P204), NaCl concentration (C_NaCl), pH value, reaction time, stirring speed and O/A were investigated to extract scandium and separate iron from the acid leaching solution. The extraction mechanism was analyzed by Fourier transform infrared spectroscopy (FT-IR) and thermodynamic theory. The single-stage extraction efficiency of scandium, iron and β_(Sc/Fe) were 99.1%, 9.4% and 1061.2, respectively, with C_NaCl of 75 g/L and X_P204 of 0.75 at solution pH value of 1.2 and stirring speed of 200 r/min for 6 min, in which a good separation effect of scandium and iron was obtained. The vibration absorption peak Sc—O was contributed to the extraction of scandium with P204. The complex [FeCl_n]³⁻ⁿ existed in the solution with adding NaCl into the acid leaching solution. The value of n was higher and the valence state of the complex [FeCl_n]³⁻ⁿ was lower with an increase of chloride concentration, which restricts the extraction efficiency of iron with P204. The extraction of three stages in the counter-current simulation experiments was carried out according to the McCabe-Thiele diagram. Gibbs free energy change (ΔG) of −5.93 kJ/mol, enthalpy change (ΔH) of 23.45 kJ/mol and entropy change (ΔH) of 98.54 J/(mol·K) were obtained in the solvent extraction proces, which indicate that the extraction reaction is easily spontaneous and endothermic and a proper increase of temperature is conducive to the extraction of scandium.

Semiconductor photocatalysis has been considered as a potential technology for the removal of organic dyes from wastewater. The development of photocatalysts with high stability and strong catalytic activity is the most important in application. Visible-light-induced NiCo₂O₄@Co₃O₄ core/shell heterojunctions were synthesized via a sol-gel method in this paper. Compared to bare NiCo₂O₄ and Co₃O₄, NiCo₂O₄@Co₃O₄ showed a remarkably enhanced removal rate towards congo red (CR) degradation with 98.4% of the removal rate to CR at 120 min under irradiation. The excellent performance of NiCo₂O₄@Co₃O₄ benefits from the effective separation of photogenerated electron-holes by forming a heterojunction, and the rapid transfer efficiency of photo-generated charge carriers results from the core/shell architectures. A mechanism that NiCo₂O₄@Co₃O₄ degrades CR to harmless inorganic substances by h⁺, •O₂⁻ and •OH during the photocatalytic process was proposed.

As clean energy, the microwave is commonly used to pretreat various ores. In this work, the microwave dielectric properties of limonitic laterite ore were measured by resonant cavity perturbation technique and the effects from microwave were systematically investigated. Results indicated that limonitic laterite had high microwave absorbance. After microwave pretreatment, the microstructure of the laterite became less aggregated and more porous and the main phase transformed from goethite to hematite that improved leaching in nitric acid (1.2 kg HNO₃/kg ore); Ni, Co, Fe, and Mg extraction ratios were 95.2%, 98.1%, 1.8% and 15%, respectively, after leaching for 60 min at 200 °C and 500 r/min. Furthermore, in the process of goethite to hematite by microwave pretreatment, the nickel-containing mineral is activated, which makes nickel be leached easily. The leaching process has high Ni extraction ratio compared to that without microwave (82%) and conventional pretreatment (90.4%). Therefore, microwave pretreatment of limonitic laterite before nitric acid pressure leaching is an effective way to improve the selectivity and extraction of the leach.

Process mineralogy of low-grade laterite nickel ore in Indonesia was systematically characterized and the beneficiation process of mineral components such as limonite, serpentine and chromite was studied on the basis of process mineralogy. The results show that the low-grade laterite nickel ore is a typical weathering sedimentary metamorphic oxidized ore, with the main valuable elements of Ni, Co and Cr and the main mineral components of limonite, serpentine, chromite, etc. There is no independent carrier mineral of Ni and Co in the raw ore, and the occurrence states of Ni and Co are relatively dispersed. For the limonite in laterite nickel mine, the nickel bearing magnetite concentrate with nickel grade of 1.98% and recovery rate of 88.42% can be obtained by reduction roasting magnetic separation process. For the serpentine in laterite nickel mine, the cobalt bearing concentrate with Co grade of 0.17% and recovery rate of 23.17% can be obtained by positive and reverse flotation process. A chromium concentrate containing 35.17% Cr₂O₃ and a recovery of 33.42% can be obtained by using the combined process of coarse and fine classification and gravity and magnetic.

Microseismic monitoring technology has become an important technique to assess stability of rock mass in metal mines. Due to the special characteristics of underground metal mines in China, including the high tectonic stress, irregular shape and existence of ore body, and complex mining methods, the application of microseismic technology is more diverse in China compared to other countries, and is more challenging than in other underground structures such as tunnels, hydropower stations and coal mines. Apart from assessing rock mass stability and ground pressure hazards induced by mining process, blasting, water inrush and large scale goaf, microseismic technology is also used to monitor illegal mining, and track personnel location during rescue work. Moreover, microseismic data have been used to optimize mining parameters in some metal mines. The technology is increasingly used to investigate cracking mechanism in the design of rock mass supports. In this paper, the application, research development and related achievements of microseismic technology in underground metal mines in China are summarized. By considering underground mines from the perspective of informatization, automation and intelligentization, future studies should focus on intelligent microseismic data processing method, e.g., signal identification of microseismic and precise location algorithm, and on the research and development of microseismic equipment. In addition, integrated monitoring and collaborative analysis for rock mass response caused by mining disturbance will have good prospects for future development.

In this paper, we present a new method of intelligent back analysis (IBA) using grey Verhulst model (GVM) to identify geotechnical parameters of rock mass surrounding tunnel, and validate it via a test for a main openings of −600 m level in Coal Mine “6.13”, Democratic People’s Republic of Korea. The displacement components used for back analysis are the crown settlement and sidewalls convergence monitored at the end of the openings excavation, and the final closures predicted by GVM. The non-linear relation between displacements and back analysis parameters was obtained by artificial neural network (ANN) and Burger-creep viscoplastic (CVISC) model of FLAC^3D. Then, the optimal parameters were determined for rock mass surrounding tunnel by genetic algorithm (GA) with both groups of measured displacements at the end of the final excavation and closures predicted by GVM. The maximum absolute error (MAE) and standard deviation (Std) between calculated displacements by numerical simulation with back analysis parameters and in situ ones were less than 6 and 2 mm, respectively. Therefore, it was found that the proposed method could be successfully applied to determining design parameters and stability for tunnels and underground cavities, as well as mine openings and stopes.

The high-pressure electro-pneumatic servo valve (HESV) is a core element of the high-pressure pneumatic servo system. The annular clearance and the rounded corner of the spool-sleeve can cause the leakage at null position, thereby affecting high-precision control and stability of the servo system. This paper investigates the effects of the clearance structure on leakage behavior at null position of the HESV. A numerical approach was employed to evaluate the effects, and then a mathematical model was established to obtain the variation law of leakage flow rate at null position. The results indicate that the leakage flow rate at null position varies linearly with supply pressure and rounded corner radius, and is nonlinear as a quadratic concave function with annular clearance. The leakage flow rate of the annular clearance and the rounded corner varies with the valve opening in an invariable-nonlinear-linear trend. A test rig system of leakage behavior at null position of the HESV was built to confirm the validity of the numerical model, which agrees well with the conducted experimental study.

In recent years, an innovative underactuated robot was developed, named as underactuated cable-driven truss-like manipulator (UCTM), to be suitable in aerospace applications. However, there has been strong consensus that the stabilization of planar underactuated manipulators without gravity is a great challenge since the system includes a second order nonholonomic constraint and most classical control methods are not suitable for this kind of system. Furthermore, the complexity of the truss-like structure results in tremendous difficulty of computational complicacy and high nonlinearity during dynamic modelling in addition to controller design. It is paramount to solve these difficulties for UCTM’s future applications. To solve the above difficulties, this paper presents a dynamic modelling method for UCTM and a trajectory tracking control method based on partial feedback linearization (PFL) that fulfills the control goal of moving UCTM from its original position to a desired position by tracking a given trajectory of the joint angles. To achieve this, a model equivalent method is proposed to make UCTM equivalent with a three-link manipulator in the sense of dynamic behavior. Then the Lagrangian equation combined with complex vector method is proposed in the dynamic modelling process of UCTM, which simplifies the derivation procedure. Based on the established dynamic model, a coordinate transformation method is proposed to transform the control force matrix into the conventional form of an underactuated system, so that the control force can be separated from the unactuated term. The PFL method in combination with the LQR control method is then proposed to realize the targets that the joint angles can track given desired trajectory. Simulation experiments are conducted to verify the correctness and effectiveness of the proposed methods.

In this work, a variable structure control (VSC) technique is proposed to achieve satisfactory robustness for unstable processes. Optimal values of unknown parameters of VSC are obtained using Whale optimization algorithm which was recently reported in literature. Stability analysis has been done to verify the suitability of the proposed structure for industrial processes. The proposed control strategy is applied to three different types of unstable processes including non-minimum phase and nonlinear systems. A comparative study ensures that the proposed scheme gives superior performance over the recently reported VSC system. Furthermore, the proposed method gives satisfactory results for a cart inverted pendulum system in the presence of external disturbance and noise.

Cooperative path planning is an important area in fixed-wing UAV swarm. However, avoiding multiple time-varying obstacles and avoiding local optimum are two challenges for existing approaches in a dynamic environment. Firstly, a normalized artificial potential field optimization is proposed by reconstructing a novel function with anisotropy in each dimension, which can make the flight speed of a fixed UAV swarm independent of the repulsive/attractive gain coefficient and avoid trapping into local optimization and local oscillation. Then, taking into account minimum velocity and turning angular velocity of fixed-wing UAV swarm, a strategy of decomposing target vector to avoid moving obstacles and pop-up threats is proposed. Finally, several simulations are carried out to illustrate superiority and effectiveness.

Understanding the temperature effect on shear behavior of the ore-backfill coupling structure is critical for the safety and stability of backfill stope under the condition of high horizontal stress in deep mining. Direct shear tests were carried out on the cemented rod-mill sand backfill (CRB) and ore-CRB (OCRB) coupling specimens at various temperatures (20, 40 and 60 °C). The shear behavior and AE characteristic parameters of OCRB at different shear directions were compared and analyzed. The results show that the temperature effect on the shear performance of CRB mainly depends on the characteristics of microstructures and main mineral phases; the performance of CRB at 40 °C is relatively good; the shear deformation of OCRB has one more “peak fluctuation stage” than CRB and has a good correlation with AE characteristic parameters. The temperature can positively or negatively impact the shear strength of OCRB, depending on the temperature and shear direction; the shear performance of OCRB along the axis direction (D1) is significantly better than that perpendicular to the axis direction (D2). The co-bearing capacity of the ore-backfill coupling structure (i.e., stopes) is closely related to the ambient temperature and principal stress orientation.

The mechanical behavior evolution characteristics of sandstone are important to the application and practice of rock engineering. Therefore, a new method and concept of deep rock mechanics testing are proposed to reveal the mechanical behavior evolution mechanism of deep roadway surrounding rock after excavation with a depth over 1000 m. High stress-seepage coupling experiments of deep sandstone under various confining pressures are conducted using GCTS. Stress — strain and permeability curves are obtained. The three-stage mechanical behavior of deep sandstone is better characterized. A platform and secondary compaction phenomena are observed. With the confining pressure increasing, the platform length gradually decreases, even disappears. In the stade I, the rigid effect of deep sandstone is remarkable. In the stage II, radial deformation of deep sandstone dominates. The transient strain of confining pressure compliance is defined, which shows three-stage evolution characteristics. In the stage III, the radial deformation is greater than the axial deformation in the pre-peak stage, but the opposite trend is observed in the post-peak stage. It is found that the dynamic permeability can be more accurately characterized by the radial strain. The relations between the permeability and stress-strain curves in various stages are revealed.

The deformation and failure of coal and rock is energy-driving results according to thermodynamics. It is important to study the strain energy characteristics of coal-rock composite samples to better understand the deformation and failure mechanism of of coal-rock composite structures. In this research, laboratory tests and numerical simulation of uniaxial compressions of coal-rock composite samples were carried out with five different loading rates. The test results show that strength, deformation, acoustic emission (AE) and energy evolution of coal-rock composite sample all have obvious loading rate effects. The uniaxial compressive strength and elastic modulus increase with the increase of loading rate. And with the increase of loading rate, the AE energy at the peak strength of coal-rock composites increases first, then decreases, and then increases. With the increase of loading rate, the AE cumulative count first decreases and then increases. And the total absorption energy and dissipation energy of coal-rock composite samples show non-linear increasing trends, while release elastic strain energy increases first and then decreases. The laboratory experiments conducted on coal-rock composite samples were simulated numerically using the particle flow code (PFC). With careful selection of suitable material constitutive models for coal and rock, and accurate estimation and calibration of mechanical parameters of coal-rock composite sample, it was possible to obtain a good agreement between the laboratory experimental and numerical results. This research can provide references for understanding failure of underground coal-rock composite structure by using energy related measuring methods.

The transient pressures induced by trains passing through a tunnel and their impact on the structural safety of the tunnel lining were numerically analyzed. The results show that the pressure change increases rapidly along the tunnel length, and the maximum value is observed at around 200 m from the entrance, while the maximum pressure amplitude is detected at 250 m from the entrance when two trains meeting in a double-track tunnel. The maximum peak pressure on the tunnel induced by a train passing through a 70 m² single-track tunnel, 100 m² double-track tunnel and two trains meeting in the 100 m² double-track tunnel at 350 km/h, are −4544 Pa, −3137 Pa and −5909 Pa, respectively. The aerodynamic pressure induced axial forces acting on the tunnel lining are only 8%, 5% and 9%, respectively, of those generated by the earth pressure. It seems that the aerodynamic loads exert little underlying influence on the static strength safety of the tunnel lining providing that the existing cracks and defects are not considered.

For geotechnical stability analysis involving the Drucker-Prager (DP) criterion, both the c-φ reduction scheme and the M-K reduction scheme can be utilized. With the aid of the second-order cone programming optimized finite element method (FEM-SOCP), a comparison of the two strength reduction schemes for the stability analysis of a homogeneous slope and a multilayered slope is carried out. Numerical investigations disclose that the FoS results calculated by the c-φ reduction scheme agree well with those calculated by the classical Morgenstern-Price solutions. However, the FoS results attained by the M-K reduction scheme may lead to conservative estimation of the geotechnical safety, particularly for the cases with large internal friction angles. In view of the possible big difference in stability analysis results caused by the M-K reduction scheme, the c-φ reduction scheme is recommended for the geotechnical stability analyses involving the DP criterion.

Cracks resulting from cyclic wetting and drying of expansive soils create discontinuities and anisotropy in the soil. The representative elementary volume (REV) defined by the continuous-media theory cannot be applied to cracked expansive soils that are considered discontinuous media. In this study, direct shear tests of three different scales (30 cm², 900 cm², 1963 cm²) and crack image analysis were carried out on undisturbed soil samples subjected to drying-wetting cycles in-situ. The REV size of expansive soil was investigated using the crack intensity factor (CIF) and soil cohesion. The results show that soil cohesion decreased with increasing sample area, and the development of secondary cracks further exacerbated the size effect of sample on cohesion of the soil. As shrinkage cracks developed, the REV size of the soil gradually increased and plateaued after 3–5 cycles. Under the same drying-wetting cycle conditions, the REV size determined using soil cohesion (REV-C) is 1.75 to 2.97 times the REV size determined using CIF (REV-CIF). Under the influence of shrinkage cracks, the average CIF is positively correlated with the REV size determined using different maximum permissible errors, with the coefficient of correlation greater than 0.9. A method for determining the REV-C based on crack image analysis is proposed, and the REV-C of expansive soil in the study area under different exposure times is given.

Wicking geotextile (WG) is considered as a possible countermeasure to reduce water content in unsaturated soil. In this research, rainfall tests were carried out to verify the drainage performance of WG. And capillary rise tests were conducted to study the effect of WG on the prevention of capillary rise. Test results indicated that WG with good drainage performance could drain gravitational and capillary water out of kaolinite soil. For kaolinite soil column with water content of 12% and compaction degree of 90%, the whole process of capillary rise in soil column with a layer of WG was a typical two-stage mode, and the maximum capillary height was about 380 mm, which provided that the WG could work as a barrier to prevent capillary rise effectively. In addition, the total vertical influential regions of WG in kaolinite soil above and below the WG layer were 400 and 100 mm, respectively.

Electric vehicle is a kind of new energy vehicle which uses batteries as energy supply unit. A huge gap in charging infrastructures will be created by the expansion of electric vehicles. The effectiveness and rationality of charging facilities will directly affect the convenience and economy of the users, as well as the safe operation of the power grid. Three types of charging facilities: charging pile, charging station and battery swap station are introduced in this paper. According to the different methods of charging infrastructure planning, the research status of the method of determining charging demand points is expounded. And the spatial distribution of charging demand points extracted by the current site selection method has a certain deviation. Then the models and algorithms of charging infrastructure optimized layout are reviewed. Currently, many researches focus on three categories optimization objectives: benefit of power company side, investment cost of charging facility and user side cost, and the genetic algorithm and particle swarm optimization are the main solving algorithms. Finally, the relative methods and development trend of the charging infrastructures optimized layout are summarized, and some suggestions on the optimized layout of electric vehicle charging infrastructures are given forward.