The driving force for using powder metallurgy (PM) mostly relies on its near net-shape ability and cost-performance ratio. The automotive application is a main market of PM industry, requiring parts with competitive mechanical or functional performance in a mass production scale. As the automobile technology transforms from traditional internal combustion engine vehicles to new energy vehicles, PM technology is undergoing significant changes in manufacturing and materials development. This review outlines the challenges and opportunities generated by the changes in the automotive technology for PM. Low-cost, high-performance and light-weight are critical aspects for future PM materials development. Therefore, the studies on PM lean-alloyed steel, aluminum alloys, and titanium alloy materials were reviewed. In addition, PM soft magnetic composite applied to new energy vehicles was discussed. Then new opportunities for advanced processing, such as metal injection molding (MIM) and additive manufacturing (AM), in automotive industry were stated. In general, the change in automotive industry raises sufficient development space for PM. While, emerging technologies require more preeminent PM materials. Iron-based parts are still the main PM products due to their mechanical performance and low cost. MIM will occupy the growing market of highly flexible and complex parts. AM opens a door for fast prototyping, great flexibility and customizing at low cost, driving weight and assembling reduction.

Display devices have significantly changed our daily life for decades, from the watches, television, to the laptop and smartphone. As the desire of advanced display device with high-resolution, long operation life and lightweight properties, several display techniques have been demonstrated. There are mainly four types of electronic display device: cathode ray tube (CRT), liquid-crystal display (LCD), organic light-emitting diode (OLED), and micro-LED. Due to the different working principles and device structures, each type of display device has its special characteristic properties. The performance of devices could be adjusted through the material selection or device design. With careful device structure regulation, not only the efficiency but also the stability would be improved. Herein, a brief review of innovative strategies towards the structure design is presented.

In the present work, samples of Al-Si-Cu piston alloy after T6 heat treatment were exposed for 2 h at temperatures ranging from 400 to 550 °C. The evolution of surface roughness and microstructure of the alloy during thermal exposure was studied by combination methods of roughness profiles, optical and scanning electron microscopy as well as XRD analysis. It is found that the roughness and mass of the alloy increase with the raise of the thermal exposure temperature, and the increasing rates of them are slow as the exposure temperature is below 500 °C, but accelerates abruptly when the temperature is higher than 500 °C. The variation of surface roughness of the alloy is closely related to phase transformation and oxidation during the thermal exposure.

The effects of rare earth ytterbium (Yb) addition and hot extrusion on the microstructure and corrosion behavior of as-cast ADC12 were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The experimental results demonstrate that both the Si phase and β-Al₅FeSi phase in the alloy with 0.9 wt% Yb have been remarkably refined, and the Al₃Yb intermetallic compound has also been obtained. The Si, β-Al₅FeSi, and rare earth phases are further refined in the alloy at 0.9 wt% Yb and hot extrusion. The results of the immersion corrosion tests and electrochemical experiments show that the corrosion current density (8.56 µA/cm²) of the alloy with 0.9 wt% Yb addition and hot extrusion is 50.6% lower than the untreated alloy (17.33 µA/cm²), and the polarization resistance (9252 Ω·cm²) was 71.3% higher than the untreated alloy (2654 Ω·cm²). The corrosion in the cathode phase in the micro-battery was refined to varying degrees attributable to the addition of Yb and hot extrusion, where the cathode reaction in the corrosion process caused a decrease of the corrosion rate.

Due to the current trend towards lightweight design in automotive industry, hollow stepped gear shafts for automobile and its radial forging process are widely investigated. Utilizing coupled finite element thermo-mechanical model, radial forging process of a hollow stepped gear shaft for automobile was simulated. The optimal combination of three process parameters including initial temperature, rotation rate and radial reduction was also selected using orthogonal design method. To examine the strain inhomogeneity of the forging workpiece, the strain inhomogeneity factor was introduced. The results reveal that the maximum effective strain and the minimum effective strain appeared in the outermost and innermost zones of different cross sections for the hollow stepped gear shaft, respectively. Optimal forging parameters are determined as a combination of initial temperature of 780 °C, rotation rate of 21°/stroke and radial reduction of 3 mm.

Presently, ilmenite concentrates from Odisha Sands Complex at Chhatrapur, India are utilized to produce TiO₂ slag by direct smelting in an electric arc furnace. However, the process involves the consumption of excess electrical energy and difficulty in handling the arc furnace due to frothing effects. A more efficient process of pre-reducing the ilmenite before smelting has been proposed in the present communication. In particular, studies have been undertaken on the reduction process of ilmenite-coke composite pellets. The difference in the reduction behaviour of raw ilmenite and ilmenite-coke composite pellets has been established and compared with that of the pre-oxidized raw pellets. The effects of various processing parameters like temperature, residence time, and reductant percentage on the metallization of composite pellets in a static bed have been investigated. Metallization of about 90% has been achieved at 1250 °C for a reduction period of 360 min with a 4°% coke composition. Furthermore, the reduced pellets have been characterized through chemical analysis, optical microscopy, field emission scanning electron microscopy and X-ray diffraction analysis. The reduction behaviour of composite pellets has also been found better than that of pre-oxidized pellets indicating the former to be more efficient.

The main objective of this paper focuses on the changes that occur in the strength and microstructural properties of sodium silicate activated fly ash based geopolymer due to varying the sulfate salt and water content. A series of tests including X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, physical adsorption and unconfined compressive strength were used to investigate this effect. The results indicate that the higher water content has an adverse effect on the alkali activation and microstructural properties of geopolymer, so the optimum mass ratio of sodium sulfate in alkali-activated geopolymer under different water-to-binder ratios shows a “peak shifting” phenomenon, i.e., the higher the water-to-binder ratio, the higher the optimum mass ratio. Lower presence of sodium sulfate has no significant effect on the alkali-activated geopolymer systems; higher addition of sodium sulfate, however, could cause the symmetrical stretching vibration of Si-O and the symmetrical stretching vibration of Si-O-Si and Al-O-Si, and promote the formation of N-A-S-H gels. Furthermore, the cement effect of the gel and sodium sulfate aggregate could improve the integrity of pore structure obviously. The maximum strength of geopolymer curing at ambient temperature was 52 MPa. This study obtains the rule that the strength properties of alkali-activated geopolymers vary with the water-to-binder ratio and sodium sulfate content. The feasibility of geopolymer co-activated by sodium sulfate and sodium silicate was investigated, and reference for engineering application of alkali-activated geopolymer in salt-bearing areas was provided.

The mechanism of oxygen pressure acid leaching of sphalerite catalyzed by Fe³⁺/Fe²⁺ self-precipitation was investigated in this study. Artificial sphalerite was fabricated with varying amounts of iron content via the sintering of ZnS and FeS and used for the pressure acid leaching experiment. The variations in the potential of the pressure leaching system were investigated by using a self-designed potential autoclave. The results showed that compared to the non-iron sphalerite, there was a violent redox reaction between the 25.70% Fe-artificial sphalerite and dissolved oxygen during the process of pressure leaching; and the catalytic mechanism was attributed to the redox couple Fe³⁺/Fe²⁺, where Fe³⁺oxidizes the H2S gas film and the reduced Fe²⁺ state is subsequently oxidized by the dissolved oxygen. Furthermore, the effect of temperature, H₂SO₄ concentration, and oxygen partial pressure on the artificial sphalerite with different iron contents was studied. The sphalerite samples with iron content were observed to dissolve more easily in sulfuric acid compared to the non-iron samples. Moreover, the activation energy of artificial sphalerite was observed to be lower in the sample with 25.70% iron content (22.26 kJ/mol) compared to that with no iron (32.31 kJ/mol); and the apparent reaction orders were obtained with respect to H₂SO₄ concentration (1.10 and 1.36) and oxygen partial pressure (1.29 and 1.41), respectively. A comprehensive kinetic model was developed on the basis of the experimental data and the fitted leaching ratio plot; and the kinetic equations for the leaching of sphalerite catalyzed by Fe³⁺/Fe²⁺ self-precipitation were determined.

In the present study, the effect of reduction of cutting fluid consumption on the surface quality and tool wear was studied. Mathematical models were developed to predict the surface roughness using response surface methodology (RSM). Analysis of variance (ANOVA) was used to investigate the significance of the developed regression models. The results showed that the coefficient of determination values (R²) for the developed models was 97.46% for dry, 89.32% for flood mode (FM), and 99.44% for MQL, showing the high accuracy of fitted models. Also, under the minimum quantity lubrication (MQL) condition, the surface roughness improved by 23%–44% and 19%–41% compared with dry and FM, respectively, and the SEM images of machined surface proved the statement. The prepared SEM images of tool rake face also showed a considerable decrease in adhesion wear. Built-up edge and built-up layer were the two main products of the adhesion wear, and energy-dispersive X-ray spectroscopy (EDX) analysis of specific points on the tool faces helped to discover the chemical compositions of adhered materials. By changing dry and FM to MQL mode, dominant mechanism of tool wear in machining aluminum alloy was significantly decreased. Breakage wear that led to early failure of cutting edge was also controlled by MQL technique.

The layout of the buckets for tunnel boring machine (TBM) directly affects the muck removal efficiency of cutterhead during excavation. In order to improve the muck removal performance for TBM, the optimal design of bucket layout was investigated. The whole muck transfer process was simulated by discrete-element method (DEM), including the muck falling, colliding, pilling up, shoveling and transferring into the hopper. The muck model was established based on size distribution analysis of muck samples from the water-supply tunnel project in Jilin Province, China. Then, the influence of the bucket number and the interval angle between buckets on muck removal performance was investigated. The results indicated that, as the number of buckets increased from four to eight, the removed muck increased by 29% and the residual volume decreased by 40.5%, and the process became steadier. Different interval angles between buckets were corresponding to different removed muck irregularly, but the residual muck number increased generally with the angles. The optimal layout of buckets for the cutterhead in this tunnel project was obtained based on the simulation results, and the muck removal performance of the TBM was verified by the actual data in the engineering construction.

In this study, the effect of varied loading ratio (mass of the explosive/mass of flyer plate) on the nature of interface, temperature and pressure developed in aluminum-steel explosive cladding is presented. Increase in the loading ratio, R, enhances the pressure developed, kinetic energy utilization and deformation work performed. Interfacial microstructures exhibit the formation of molten layer at few spots, owing to the increase in temperature beyond the melting point of parent alloy. The increase in temperature and the quantum of pressure developed were determined by numerical simulation performed in Ansys AUTODYN by employing smoothed particle hydrodynamics (SPH) method. The positioning of the experimental conditions on the weldability window is presented as well.

This paper addresses the problem of three-dimensional trajectory tracking control for underactuated autonomous underwater vehicles in the presence of parametric uncertainties, environmental disturbances and input saturation. First, a virtual guidance control strategy is established on the basis of tracking error kinematics, which resolves the overall control system into two cascade subsystems. Then, a first-order sliding mode differentiator is introduced in the derivation to avoid tedious analytic calculation, and a Gaussian error function-based continuous differentiable symmetric saturation model is explored to tackle the issue of input saturation. Combined with backstepping design techniques, the neural network control method and an adaptive control approach are used to estimate composite items of the unknown uncertainty and approximation errors. Meanwhile, Lyapunov-based stability analysis guarantees that control error signals of the closed-loop system are uniformly ultimately bounded. Finally, simulation studies are conducted for the trajectory tracking of a moving target and a spiral line to validate the effectiveness of the proposed controller.

Vibrations of a rotor-bearing system (RBS) can be affected by the frictional forces between the components of the inherent bearings. Thus, an in-depth investigation of the influences of the frictional moments of the bearings on the vibrations of the RBS can be helpful for understanding the vibration mechanisms in the rotating machinery. In this study, an improved dynamic model of a RBS considering different frictional force models is presented. A comparative investigation on the influences of the empirical and analytical frictional force models on the vibration characteristics of the RBS is proposed. The empirical frictional force models include Palmgren’s and SKF’s models. The analytical frictional force model considers the rolling friction caused by the radial elastic material hysteresis, slipping friction between the ball and races, viscosity friction caused by the lubricating oil, and contact friction between the ball and cage. The influences of the external load and rotational speed on the vibrations of the RBS are analyzed. The comparative results show that the analytical frictional force model can give a more reasonable method for formulating the effects of the friction forces in the bearings on the vibrations of the RBS. The results also demonstrate that the friction forces in the bearings can significantly affect the vibrations of the RBSs.

The carbon dioxide removal system is the most critical system for controlling CO₂ mass concentration in long-term manned spacecraft. In order to ensure the controlling CO₂ mass concentration in the cabin within the allowable range, the state of CO₂ removal system needs to be estimated in real time. In this paper, the mathematical model is firstly established that describes the actual system conditions and then the Galerkin-based extended Kalman filter algorithm is proposed for the estimation of the state of CO₂. This method transforms partial differential equation to ordinary differential equation by using Galerkin approaching method, and then carries out the state estimation by using extended Kalman filter. Simulation experiments were performed with the qualification of the actual manned space mission. The simulation results show that the proposed method can effectively estimate the system state while avoiding the problem of dimensional explosion, and has strong robustness regarding measurement noise. Thus, this method can establish a basis for system fault diagnosis and fault positioning.

Understanding the impacts of co-invasion of multiple invaders on soil bacterial communities is significant in understanding the mechanisms driving successful invasion. This study aimed to determine the response of soil bacterial communities to co-invasion of two invaders daisy fleabane (Erigeron annuus) and Canada goldenrod (Solidago canadensis). Daisy fleabane and/or Canada goldenrod invasion significantly enhanced the operational taxonomic unit richness, Shannon index, and Chao1 index of soil bacterial communities. Canada goldenrod under light degree of invasion and co-invasion of daisy fleabane and Canada goldenrod regardless of invasion degree signally improved the ACE index of soil bacterial communities. Thus, the two invaders can enhance soil bacterial diversity and richness to facilitating subsequent invasion due to the fact that higher soil bacterial diversity and richness can enhance the levels of soil function and nutrients acquisition of plant species. ACE index of soil bacterial communities subjected to co-invasion of daisy fleabane and Canada goldenrod regardless of invasion degree was greater than that under the independent invasion of either daisy fleabane or Canada goldenrod. Hence, co-invasion of the two invaders can impose synergistic impacts on soil bacterial richness, which may build a preferable soil micro-environment via the intensified soil bacterial communities, which is contributive to their following invasion.

This paper investigates the main scale analysis of the aerodynamic noise in the foremost bogie area by the large-eddy simulation (LES) and the Ffowcs Williams-Hawkings (FW-H) analogy. The mechanism of the aerodynamic noise in this area has been excavated. The aerodynamic excitation results show that the bogie divides the bogie compartment into two cavities, each of which contains a large circulating flow and presents multi-peak characteristics in the frequency domain. The far-field noise results suggest that in the speed range of 200–350 km/h, the aerodynamic noise mechanism in the bogie area is the same. Cavity noise is the main noise mechanism in the foremost bogie area, and the bogie divides the bogie cabin into two cavities, thereby changing the aerodynamic noise in this area.

This study for the first time demonstrates that some of the so-called clay-sized mudstones observed by the naked eye, such as clay-sized black mudstones and clay-sized oil shales, which are rich in black organic matter (including oil and asphaltene), in the Chang 73 Submember of the Upper Triassic Yanchang Formation in the Ordos Basin of China are actually clay-sized tuffaceous rocks (including tuff, sedimentary tuff and tuffaceous sedimentary rock) with high hydrocarbon generation capacities. Thus, these rocks can be defined as clay-sized tuffaceous source rocks. Identification of this lithology has important theoretical and practical significance for the exploration and development of shale oil in the Chang 7 Member. Through the macroscopic observation of drill cores and outcrop profiles, microscopic observation of electron probe thin sections and whole-rock inorganic geochemical analysis (including major, trace and rare earth elements), this work demonstrates that the organic matter-rich clay-sized tuffaceous rocks, especially clay-sized tuffs, have the following characteristics. First, the clay-sized tuffaceous rocks with little black organic matter are mainly greyish white, yellowish brown and purplish grey, and mixed colors occur in areas with strong bentonite lithification. Second, the clay-sized tuffaceous rocks have experienced strong devitrification and recrystallization, forming abundant flaky aluminosilicate minerals with directional arrangement. In thin sections under a polarizing microscope, the interference colors generally show regular alternation between the lowest interference color of first-order yellow and the highest interference color of second-order blue-green. Third, the rock samples plot in the igneous rock field in the TiO₂-SiO₂ cross-plot and exhibit similar trace element and rare earth element patterns on spider diagrams, indicating that the samples are derived from the same source. The results prove that clay-sized tuffaceous rocks may be widespread in the Chang 73 Submember of the Upper Triassic Yanchang Formation in the Ordos Basin, China.

Large-scale gypsum rocks associated with world-class Pb-Zn ore formations are widely distributed in the Lanping Basin, Sowthwest China. Geochemical studies alongside field investigations were conducted in this study to determine the source and evolutionary processes of the gypsum rocks in this area. The gypsum sequences in the Lanping Basin developed in two formations: the Triassic Sanhedong Formation and the Paleogene Yunlong Formation. The gypsum hosted in the former displays a primary thick-banded structure with δ³⁴S_V-CDT values in the range of 14.5‰–14.8‰. Combined with the ⁸⁷Sr/⁸⁶Sr values (0.707737–0.707783) of limestone, it can be suggested that the Sanhedong Formation is of marine origin. In contrast, the gypsum from the Paleogene Yunlong Formation is characterized by the dome, bead and diapiric salt structures, wider range of both ⁸⁷Sr/⁸⁶Sr (0.707695–0.708629) and δ³⁴S_V-CDT values (9.6‰–17‰), thus indicating a marine source but with the input of continental materials. The initial layered salt formations were formed by chemical deposition in a basin and were later intensely deformed by collisional orogeny during the Himalaya period. As a result, variable salt structures were formed. We hereby propose an evolutionary model to elucidate the genesis of the gypsum formations in the Lanping Basin.

Thermal shocking effect occurs when the coalbed methane (CBM) reservoirs meet liquid nitrogen (LN2) of extremely low temperature. In this study, 3D via X-ray microcomputer tomography (µCT) and scanning electron microscope (SEM) are employed to visualize and quantify morphological evolution characteristics of fractures in coal after LN2 thermal shocking treatments. LN2 thermal shocking leads to a denser fracture network than its original state with coal porosity growth rate increasing up to 183.3%. The surface porosity of the μCT scanned layers inside the coal specimen is influenced by LN2 thermal shocking which rises from 18.76% to 215.11%, illustrating the deformation heterogeneity of coal after LN2 thermal shocking. The cracking effect of LN2 thermal shocking on the surface of low porosity is generally more effective than that of high surface porosity, indicating the applicability of LN2 thermal shocking on low-permeability CBM reservoir stimulation. The characteristics of SEM scanned coal matrix in the coal powder and the coal block after the LN2 thermal shocking presented a large amount of deep and shallow progressive scratch layers, fracture variation diversity (i.e. extension, propagation, connectivity, irregularity) on the surface of the coal block and these were the main reasons leading to the decrease of the uniaxial compressive strength of the coal specimen.

To reveal the bearing capacity of the X-section concrete piles pile raft foundation in silica sand, a series of vertical load tests are carried out. The X-section concrete piles are compared with circular section pile with the same section area. The load-settlement curves, axial force and skin friction, strain on concave and convex edge of the pile, pile-sand stress ratio, distributions of side and tip resistance are presented. The results show that bearing capacity of the X section concrete pile raft foundation is much larger than that of the circular pile raft foundation. Besides, compared with the circular pile, the peak axial force of X-section piles under raft is deeper and smaller while the neutral point of X-section concrete pile is deeper. Moreover, the strain on the concave edge is much larger than that on the convex edge of the pile, and the convex edge has more potential in bearing capacity as the vertical load increases. The X-section pile has higher pile-sand stress ratios and load-sharing between side resistance and tip resistance. Above all, the X-section concrete pile can significantly increase the bearing capacity of pile-raft foundations in silica sand.

The addition of basement beneath existing building changes the underpinning pile from fully embedded to partially embedded, and thus influences the mechanical properties of pile. In the past, scholars paid attention to the change in the bearing capacity of pile but neglected the difference of dynamic characteristics before and after construction, and potential changes in stress history of remaining soil are also ignored. In this work, a calculation model is built to investigate the influence of excavation on dynamic impedance of underpinning pile considering the effect of stress history. The soil is simulated by the dynamic Winkler foundation, which is characterized by springs and dashpots. Properties of remaining soil after excavation are updated to consider the effect of stress history through modifying the initial shear modulus and related parameters. The dynamic impedance of pile after excavation is obtained based on the transfer matrix method. The parameter study is carried out to evaluate the dynamic impedance with various excavation depths, considering or ignoring stress history effect, and various element lengths. The results show that shallow soil plays an important role to dynamic impedance, and overestimated dynamic impedance is obtained if not considering the stress history effect.

In order to provide guideline for choosing a suitable tube-wall thickness (δ) for the micro-jet methane diffusion flame, the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work. The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness. Subsequently, the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed, strain effect and conjugate heat exchange. The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit. A smaller strain effect can induce the increase of the blow-off limit from δ=0.1 to 0.2 mm, and a worse heat recirculation effect can induce the decrease of the blow-off limit from δ=0.2 to 0.4 mm. The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel. The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit at δ=0.2 mm. Therefore, a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.

The second organization’s name was wrong and it should be replaced as follows: Kunming Training Corps, Fire and Rescue Bureau, Ministry of Emergency Management, Kunming 650208, China

The First author’s name was wrong and it should be replaced as HUANG Jing(黄晶)^{1, 3}.