Wear behaviors of a peak-aged Cu-15Ni-8Sn alloy fabricated by powder metallurgy were investigated. The results indicated that the friction coefficients and the wear rates of Cu-15Ni-8Sn alloy within a normal load range of 50-700 N and a sliding speed range of 0.05-2.58 m/s were less than 0.14 and 2.8×10⁻⁶ mm³/mm, respectively. Stribeck-like curve and wear map were developed to describe the oil-lubrication mechanism and wear behavior. The equation of the dividing line between zones of safe and unsafe wear life was determined. Lubricating oil was squeezed into micro-cracks under severe wear conditions. In addition, the lubricating oil reacted with Cu-15Ni-8Sn alloy to generate the corresponding sulfides, which hindered the repair of micro-cracks, promoted cracks growth, and led to delamination. This work has established guidelines for the application of the Cu-15Ni-8Sn alloy under oil-lubricated conditions through developing wear map.

After a standard heat treatment, the microstructural evolution with time during isothermal aging at 850 °C and its effect on the creep rupture properties of the Ni-base superalloy M4706 at 870 °C and 370 MPa are investigated. It is found that as the aging time increases from 0 to 5000 h, the average diameter of coarse γ’ increases from 241 to 484 nm, and the distribution of the carbides at grain boundaries changes from discontinuous to continuous. Moreover, experimental observations on the microstructures of all the crept specimens reveal that dislocation bypassing controls the creep deformation. Thus, it is concluded that the transitions in the microstructures result in the degeneration of the creep rupture properties of the experimental alloy with aging time.

Selective laser melting (SLM) technology is the prevailing method of manufacturing components with complex geometries. However, the cost of the additive manufacturing (AM) fine powder is relatively high, which significantly limits the development of the SLM. In this study, the 316L fine powder and coarse powder with a mass ratio of 80:20, 70:30 and 60:40 were mixed using a ball milling and the samples with a relative density greater than 97% were prepared by SLM. The results show that the intricate temperature gradients and surface tension gradients in SLM will produce Marangoni flow, forming a typical molten pool morphology, cellular and strip subgrain structures. And as the proportion of coarse powder increases, the scanning track morphology changes from smooth to undulating; the morphology of the molten pool and subgrain structure are weakened. Meanwhile, the unmelted particles appear on the surface of the SLM sample. On the premise of an introducing appropriate amount of large particle size powder (20%), the SLM samples still have good mechanical properties (662 MPa, 47%).

Oxygen reduction reaction (ORR) plays a crucial role in many energy storage and conversion devices. Currently, the development of inexpensive and high-performance carbon-based non-precious-metal ORR catalysts in alkaline media still gains a wide attention. In this paper, the mesoporous Fe-N/C catalysts were synthesized through SiO₂-mediated templating method using biomass soybeans as the nitrogen and carbon sources. The SiO₂ templates create a simultaneous optimization of both the surface functionalities and porous structures of Fe-N/C catalysts. Detailed investigations indicate that the Fe-N/C3 catalyst prepared with the mass ratio of SiO₂ to soybean being 3:4 exhibits brilliant electrocatalytic performance, excellent long-term stability and methanol tolerance for the ORR, with the onset potential and the half-wave potential of the ORR being about 0.890 V and 0.783 V (vs RHE), respectively. Meanwhile, the desired 4-electron transfer pathway of the ORR on the catalysts can be observed. It is significantly proposed that the high BET specific surface area and the appropriate pore-size, as well as the high pyridinic-N and total nitrogen loadings may play key roles in enhancing the ORR performance for the Fe-N/C3 catalyst. These results suggest a feasible route based on the economical and sustainable soybean biomass to develop inexpensive and highly efficient non-precious metal electrochemical catalysts for the ORR.

To make clear the influence of abrasive hardness on the erosion effect, the erosion experiments of abrasive air jet with the same impact energy were carried out. The influence of abrasive hardness on the erosion effect is clarified by comparing the different erosion depths. The main conclusions are as follows. Under the same mass flow rate and mesh number, the abrasive with a higher density needs greater pressure irrespective of hardness. After erosion damage, the abrasive size exhibits a Weibull distribution. The shape parameter β and Weibull distribution function of four types of abrasives are derived by the least squares method; moreover, β is found to have a quadratic relation with abrasive hardness. The results of the erosion experiments show that abrasive hardness and erosion depth are quadratically related. By calculating the increase in surface energy after abrasive erosion crushing, it is found that abrasive hardness has a quadratic relation with surface energy and that the increases in erosion depth and surface energy consumption are basically identical. In conclusion, the effect is a soft abrasive impact when the ratio of abrasive hardness (H_a) to the material hardness (H_m) is <2.6, and it is a hard abrasive impact when H_a/H_m >3.

To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy, quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liquid quenching using an MTS810.23 universal testing machine and split-Hopkinson pressure bar (SHPB). The experimental data were fitted to obtain the Johnson–Cook constitutive model parameters of the alloy. Simulations of the machining process were carried out using the Deform-3D finite element software. The results showed that the rheological stress increased with the increase in strain rate and the decrease in temperature. The increase in the cutting speed and feed caused the cutting temperature to rise sharply, whereas the influence of the cutting amount on the cutting temperature was weak. Because of the presence of chip nodules, there was extremum in the cutting force vs cutting speed curves. The increase in the feed and cutting depth increased the cutting area Ac, so the cutting force also increased. The simulation results were verified by experiments. The simulation predictions were in good agreement with the test values, and the cutting force and temperature variations with the cutting parameters were the same. Thus, the correctness of the 7A09 aluminum alloy finite element model was verified.

In order to improve the hot corrosion resistance of DZ125 alloy, Ce-Y modified aluminum coatings were prepared on DZ125 alloy by pack cementation process at 950 °C for 2 h. The microstructure, phase constitution and formation mechanism of the coatings were investigated. The hot corrosion behaviors of DZ125 alloy and the coatings in molten salt environment of 25%K₂SO₄+75%Na₂SO₄ (mass fraction) at 900 °C were studied. Results show that the obtained Al-Ce-Y coatings were mainly composed of Al₃Ni₂, Al₃Ni and Cr₇Ni₃, with a thickness of about 120 μm. After hot corrosion test, DZ125 alloy suffered catastrophic hot corrosion and serious internal oxidation and internal sulfidation arose. Two layers of corrosion products formed on surfaces of DZ125 alloy, including the outer layer consisting of Cr₂O₃ and NiCr₂O₄, and the inner layer of Al₂O₃, Ni₃S₂ and Ni-base solid solution. After being coated with Al-Ce-Y coating, the hot corrosion resistance of DZ125 alloy is improved notably, due to the formation of a dense scale mainly consisting of Al-rich Al₂O₃ in the coating layer.

Three-dimensional ordered macro/mesoporous carbon (3DOM/m-C) with high specific surface area was synthesized by colloid crystal template method with chemical activation by KOH and used as the adsorbent for removing malachite green (MG) in aqueous solution. The microstructures of the adsorbents were characterized by FESEM, TEM and BET, and the effects of initial dye concentration, contact time, solution pH, and temperature on adsorption performance were investigated. The results show that the 3DOM/m-C exhibits extremely high adsorption capacity of 3541.1 mg/g within 2 h, which could be attributed to the novel ordered hierarchical structure with mesopores on three-dimensional ordered macroporous carbon walls. And the adsorption behavior conforms to the pseudo-second-order kinetic and Langmuir adsorption isotherm. 3DOM/m-C can be recycled after being desorbed by absolute ethanol, and still maintains a high capacity of 2762.06 mg/g after 5 cycles.

Wind energy sources have different structures and functions from conventional power plants in the power system. These resources can affect the exchange of active and reactive power of the network. Therefore, power system stability will be affected by the performance of wind power plants, especially in the event of a fault. In this paper, the improvement of the dynamic stability in power system equipped by wind farm is examined through the supplementary controller design in the high voltage direct current (HVDC) based on voltage source converter(VSC) transmission system. In this regard, impacts of the VSC HVDC system and wind farm on the improvement of system stability are considered. Also, an algorithm based on controllability (observability) concept is proposed to select most appropriate and effective coupling between inputs-outputs (IO) signals of system in different work conditions. The selected coupling is used to apply damping controller signal. Finally, a fractional order PID controller (FO-PID) based on exchange market algorithm (EMA) is designed as damping controller. The analysis of the results shows that the wind farm does not directly contribute to the improvement of the dynamic stability of power system. However, it can increase the controllability of the oscillatory mode and improve the performance of the supplementary controller.

This paper studies the global fixed time synchronization of complex dynamical network, including non-identical nodes with disturbances and uncertainties as well as input nonlinearity. First, a novel fixed time sliding manifold is constructed to achieve the fixed time synchronization of complex dynamical network with disturbances and uncertainties. Second, a novel sliding mode controller is proposed to realize the global fixed time reachability of sliding surfaces. The outstanding feature of the designed control is that the fixed convergence time of both reaching and sliding modes can be adjusted to the desired values in advance by choosing the explicit parameters in the controller, which does not rest upon the initial conditions and the topology of the network. Finally, the effectiveness and validity of the obtained results are demonstrated by corresponding numerical simulations.

The application of multiple UAVs in complicated tasks has been widely explored in recent years. Due to the advantages of flexibility, cheapness and consistence, the performance of heterogeneous multi-UAVs with proper cooperative task allocation is superior to over the single UAV. Accordingly, several constraints should be satisfied to realize the efficient cooperation, such as special time-window, variant equipment, specified execution sequence. Hence, a proper task allocation in UAVs is the crucial point for the final success. The task allocation problem of the heterogeneous UAVs can be formulated as a multi-objective optimization problem coupled with the UAV dynamics. To this end, a multi-layer encoding strategy and a constraint scheduling method are designed to handle the critical logical and physical constraints. In addition, four optimization objectives: completion time, target reward, UAV damage, and total range, are introduced to evaluate various allocation plans. Subsequently, to efficiently solve the multi-objective optimization problem, an improved multi-objective quantum-behaved particle swarm optimization (IMOQPSO) algorithm is proposed. During this algorithm, a modified solution evaluation method is designed to guide algorithmic evolution; both the convergence and distribution of particles are considered comprehensively; and boundary solutions which may produce some special allocation plans are preserved. Moreover, adaptive parameter control and mixed update mechanism are also introduced in this algorithm. Finally, both the proposed model and algorithm are verified by simulation experiments.

As the popularity of open source projects, the volume of incoming pull requests is too large, which puts heavy burden on integrators who are responsible for accepting or rejecting pull requests. An accepted pull request prediction approach can help integrators by allowing them either to enforce an immediate rejection of code changes or allocate more resources to overcome the deficiency. In this paper, an approach CTCPPre is proposed to predict the accepted pull requests in GitHub. CTCPPre mainly considers code features of modified changes, text features of pull requests’ description, contributor features of developers’ previous behaviors, and project features of development environment. The effectiveness of CTCPPre on 28 projects containing 221096 pull requests is evaluated. Experimental results show that CTCPPre has good performances by achieving accuracy of 0.82, AUC of 0.76 and F1-score of 0.88 on average. It is compared with the state of art accepted pull request prediction approach RFPredict. On average across 28 projects, CTCPPre outperforms RFPredict by 6.64%, 16.06% and 4.79% in terms of accuracy, AUC and F1-score, respectively.

Process control is an effective approach to reduce the NO_x emission from sintering flue gas. The effects of different materials adhered on coke breeze on NO_x emission characteristics and sintering performance were studied. Results showed that the coke breeze adhered with the mixture of CaO and Fe₂O₃ or calcium ferrite significantly lowers the NO_x emission concentration and conversion ratio of fuel-N to NO_x. Pretreating the coke with the mixture of lime slurry and iron ore fines helped to improve the granulation effect, and optimize the carbon distribution in granules. When the mass ratio of coke breeze, quick lime, water and iron ore fines was 2:1:1:1, the average NO_x emission concentration was decreased from 220 mg/m³ to 166 mg/m³, and the conversion ratio of fuel-N was reduced from 54.2% to 40.9%.

Adding a moving baffle to the drum is a new way to enhance the motion and mixing of particles in rotating drums. To obtain its influence on binary particles, horizontal rotating drums provided with a moving baffle were investigated by discrete element method (DEM). At Ω=15 r/min, increasing the length of moving baffle can increase the fluctuation amplitude of average particle velocity. At Ω=60 r/min, the influence of the moving baffle on the average velocity fluctuation tends to be more random. At both rotational speeds, the moving baffle causes the average particle velocity to fluctuate more sharply. The moving baffle can enhance particle mixing. At Ω=15 r/min, the moving baffle with length of δ=1/3 can best enhance particle mixing. However, at Ω=60 r/min, only the moving baffle with a specific length (δ=1/4) can enhance mixing. This basic research has a positive reference value for the application of the moving baffle in industry.

Aiming at wind turbines, the opportunistic maintenance optimization is carried out for multi-component system, where minimal repair, imperfect repair, replacement as well as their effects on component’s effective age are considered. At each inspection point, appropriate maintenance mode is selected according to the component’s effective age and its maintenance threshold. To utilize the maintenance opportunities for the components among the wind turbines, opportunistic maintenance approach is adopted. Meanwhile, the influence of seasonal factor on the component’s failure rate and improvement factor’s decrease with the increase of repair’s times are also taken into account. The maintenance threshold is set as the decision variable, and an opportunistic maintenance optimization model is proposed to minimize wind turbine’s life-cycle maintenance cost. Moreover, genetic algorithm is adopted to solve the model, and the effectiveness is verified with a case study. The results show that based on the component’s inherent reliability and maintainability, the proposed model can provide optimal maintenance plans accordingly. Furthermore, the higher the component’s reliability and maintainability are, the less the times of repair and replacement will be.

Discernment of seismic soil liquefaction is a complex and non-linear procedure that is affected by diversified factors of uncertainties and complexity. The Bayesian belief network (BBN) is an effective tool to present a suitable framework to handle insights into such uncertainties and cause–effect relationships. The intention of this study is to use a hybrid approach methodology for the development of BBN model based on cone penetration test (CPT) case history records to evaluate seismic soil liquefaction potential. In this hybrid approach, naive model is developed initially only by an interpretive structural modeling (ISM) technique using domain knowledge (DK). Subsequently, some useful information about the naive model are embedded as DK in the K2 algorithm to develop a BBN-K2 and DK model. The results of the BBN models are compared and validated with the available artificial neural network (ANN) and C4.5 decision tree (DT) models and found that the BBN model developed by hybrid approach showed compatible and promising results for liquefaction potential assessment. The BBN model developed by hybrid approach provides a viable tool for geotechnical engineers to assess sites conditions susceptible to seismic soil liquefaction. This study also presents sensitivity analysis of the BBN model based on hybrid approach and the most probable explanation of liquefied sites, owing to know the most likely scenario of the liquefaction phenomenon.

Water inrush is one of the most serious geological hazards in underground engineering construction. In order to effectively prevent and control the occurrence of water inrush, a new attribute interval recognition theory and method is proposed to systematically evaluate the risk of water inrush in karst tunnels. Its innovation mainly includes that the value of evaluation index is an interval rather than a certain value; the single-index attribute evaluation model is improved non-linearly based on the idea of normal distribution; the synthetic attribute interval analysis method based on improved intuitionistic fuzzy theory is proposed. The TFN-AHP method is proposed to analyze the weight of evaluation index. By analyzing geological factors and engineering factors in tunnel zone, a multi-grade hierarchical index system for tunnel water inrush risk assessment is established. The proposed method is applied to ventilation incline of Xiakou tunnel, and its rationality and practicability is verified by comparison with field situation and evaluation results of other methods. In addition, the results evaluated by this method, which considers that water inrush is a complex non-linear system and the geological conditions have spatial variability, are more accurate and reliable. And it has good applicability in solving the problem of certain and uncertain problem.

Water invasion is a common phenomenon in gas reservoirs with active edge-and-bottom aquifers. Due to high reservoir heterogeneity and production parameters, carbonate gas reservoirs feature exploitation obstacles and low recovery factors. In this study, combined core displacement and nuclear magnetic resonance (NMR) experiments explored the reservoir gas–water two-phase flow and remaining microscopic gas distribution during water invasion and gas injection. Consequently, for fracture core, the water-phase relative permeability is higher and the co-seepage interval is narrower than that of three pore cores during water invasion, whereas the water-drive recovery efficiency at different invasion rates is the lowest among all cores. Gas injection is beneficial for reducing water saturation and partially restoring the gas-phase relative permeability, especially for fracture core. The remaining gas distribution and the content are related to the core properties. Compared with pore cores, the water invasion rate strongly influences the residual gas distribution in fracture core. The results enhance the understanding of the water invasion mechanism, gas injection to resume production and the remaining gas distribution, so as to improve the recovery factors of carbonate gas reservoirs.

Aiming to investigate the fatigue damage mechanism and bearing characteristics of multi-pillar system under cyclic loading, a series of axial cyclic loading tests with different cyclic amplitudes were carried out on triple-pillar marble specimens. The acoustic emission (AE) and digital image correlation (DIC) were jointly applied to monitoring and recording damage evolution and failure behavior of each pillar, which reproduced the cataclysmic instability process of underground pillar groups. Experimental results indicated that the cyclic amplitude exceeding the threshold of damage initiation weakened the resistance to deformation, resulting in obvious release of dissipated energy and the reduction of bearing capacity. Conversely, after low-amplitude cyclic loading, both the pre-peak bearing capacity and the post-peak ductility of the pillar system increased due to the compaction of initial defects, indicating that the peak bearing capacity was closely related to the extent of pre-peak fatigue damage. The axial strain of each pillar was measured by DIC virtual extensometer to present the damage extent during cyclic loading phase. Meanwhile, fracture evolution of typical load drop points was also characterized by transverse strain fields (ε_xx), and observations showed that the damage extent of key pillar undergoing high-amplitude cyclic loads was more serious and violent, accompanied by the ejection of rock debris and loud noises.

As a frequently-used roadbed filler, soil-rock mixture is often in the environment of freeze-thaw cycles and different confining pressures. In order to study the freeze-thaw damage mechanism of elastic modulus of soil-rock mixtures at different confining pressures, the concept of meso-interfacial freeze-thaw damage coefficient is put forward and the meso-interfacial damage phenomenon of soil-rock mixtures caused by the freeze-thaw cycle environment is concerned; a double-inclusion embedded model for elastic modulus of soil-rock mixtures in freezing-thawing cycle is proposed. A large triaxial test was performed and the influences of confining pressure and experimental factors on elastic modulus of soil-rock mixtures were obtained, and then the accuracy of the double-inclusion embedded model to predict the elastic modulus of soil-rock mixtures in freezing-thawing cycle is verified. Experiment results showed that as to soil-rock mixtures, with the increase of confining pressure, the elastic modulus increases approximately linearly. The most crucial factors to affect the elastic modulus are rock content and compaction degree at the same confining pressure; the elastic modulus increases with the increase of rock content and compactness; as the number of freeze-thaw cycles increases, the freeze-thaw damage coefficient of meso-structural interface and the elastic modulus decrease.

Despite appropriate design of girder under bending and shear, the deflection of long steel girders usually exceeds the allowable range, and therefore the structural designers encounter challenges in this regard. Considering significant features of the cables, namely, low weight, small cross section, and high tensile strength, they are used in this research so as to control the deflection of long girder bridges, rather than increasing their heights. In this study, theoretical relations are developed to calculate the increase in pre-tensioning force of V-shaped steel cables under external loading as well as the deflection of steel girder bridges with V-shaped cables and different support conditions. To verify the theoretical relations, the steel girder bridge is modeled in the finite element ABAQUS software with different support conditions without cable and with V-shaped cables. The obtained results show that the theoretical relations can appropriately predict the deflection of girder bridge with V-shaped cables and different support conditions. In this study, the effects of the distance from support on the deflection of mid span are studied in both simply supported and fixed supported girder bridge so as to obtain the appropriate distance from support causing the minimum deflection.

In this paper, a new micro-creep model of salt rock is proposed based on a linear parallel bonded model (LPBM) using the two-dimensional particle flow code (PFC2D). The power function weakening form is assumed to describe the variation of the parallel bonded diameter (PBD) over time. By comparing with the parallel-bonded stress corrosion (PSC) model, a smaller stress fluctuation and smoother creep strain-time curves can be obtained by this power function model at the same stress level. The validity and adaptability of the model to simulate creep deformation of salt rock are verified through comparing the laboratory creep test curves and the Burgers model fitting result. The numerical results reveal that this model can be capable of capturing the creep deformation and damage behavior from the laboratory observations.

A wave equation of rock under axial static stress is established using the equivalent medium method by modifying the Kelvin-Voigt model. The analytical formulas of longitudinal velocity, space and time attenuation coefficients and response frequency are obtained by solving the equation using the harmonic method. A series of experiments on stress wave propagation through rock under different axial static stresses have been conducted. The proposed models of stress wave propagation are then verified by comparing experimental results with theoretical solutions. Based on the verified theoretical models, the influences of axial static stress on longitudinal velocity, space and time attenuation coefficients and response frequency are investigated by detailed parametric studies. The results show that the proposed theoretical models can be used to effectively investigate the effects of axial static stress on the stress wave propagation in rock. The axial static stress influences stress wave propagation characteristics of porous rock by varying the level of rock porosity and damage. Moreover, the initial porosity, initial elastic modulus of the rock voids and skeleton, viscous coefficient and vibration frequency have significant effects on the P-wave velocity, attenuation characteristics and response frequency of the stress wave in porous rock under axial static stress.

With the increased use of natural gas, it is valuable to study energy recovery ratio in the natural gas pressure reduction stations (PRSs). This paper focused on recovering the energy in PRSs as well as low-grade waste heat by a coupled power generation system (CPGS). The CPGS integrates a natural gas expansion (NGE) subsystem and an organic Rankine cycle (ORC) subsystem driven by low-temperature waste heat. Firstly, a comparative analysis is carried out between the separated natural gas expansion system and the separated ORC system. Then, the effects of heat source conditions, upstream pressure of natural gas and the isentropic efficiency of the natural gas expander are investigated. At last, working fluids selection is conducted with respect to two different pressure ranges of natural gas. The results show that there is an optimal temperature and mass flow rate of the heat source that maximizes the system exergy efficiency. With the increase of the upstream pressure of natural gas, the net power output and waste heat recovery factor increase while the system exergy efficiency has an optimal point. Furthermore, the isentropic efficiency of the natural gas expander has a great influence on the net power output of the system.

Seeking for innovative structures with higher mechanical performance is a continuous target in railway vehicle crashworthiness design. In the present study, three types of hexagonal reinforced honeycomb-like structures were developed and analyzed subjected to out-of-plane compression, namely triangular honeycomb (TH), double honeycomb (DH) and full inside honeycomb (FH). Theoretical formulas of average force and specific energy absorption (SEA) were constructed based on the energy minimization principle. To validate, corresponding numerical simulations were carried out by explicit finite element method. Good agreement has been observed between them. The results show that all these honeycomb-like structures maintain the same collapsed stages as conventional honeycomb; cell reinforcement can significantly promote the performance, both in the average force and SEA; full inside honeycomb performs better than the general, triangular and double schemes in average force; meanwhile, its SEA is close to that of double scheme; toroidal surface can dissipate higher plastic energy, so more toroidal surfaces should be considered in design of thin-walled structure. These achievements pave a way for designing high-performance cellular energy absorption devices.