Abstract:Aero-engine accessory gearbox bearings operate under high speed,high temperature,and complex load conditions,where their lubrication state directly affects engine reliability and service life.To address the shortcomings of conventional side-jet lubrication in oil distribution uniformity and cooling efficiency,this study investigates the under-race lubrication scheme for accessory gearbox bearings.Based on a developed local frictional heat model and a fluid-thermal-structural coupled two-phase oil-gas flow model,computational fluid dynamics methods were employed to systematically analyze the effects of oil hole diameter,number of holes,oil supply rate,and rotational speed on the internal lubrication characteristics of the bearings.Results show that increasing the oil hole diameter from 0.4 mm to 0.8 mm slightly reduces the oil volume fraction in the bearing cavity;increasing the number of holes from 4 to 8 significantly improves circumferential uniformity;increasing the oil supply from 0.01 L/min to 0.25 L/min steadily raises the total oil content in the cavity and enhances lubrication coverage on the outer ring;as the speed increases from 2 000 r/min to 10 000 r/min,the oil distribution gradually extends from the inner ring to the entire bearing cavity,while the effect of gravity is significantly reduced.The study indicates that under-race lubrication significantly improves lubrication coverage and uniformity,providing a theoretical basis and reference for efficient bearing lubrication design and oil supply system optimization in aero-engines.

Abstract:As a core component of high-end equipment,spherical plain bearings transmit loads and enable complex motions such as tilting and oscillation,and widely used in critical fields like military and aerospace.Their precision forming technology directly determines the forming quality and service performance of spherical plain bearings.Two common forming processes for integral self-lubricating spherical plain bearings were introduced:Mold extrusion forming and rotary extrusion forming.The application of finite element analysis in process optimization is briefly discussed.The current state of forming technology both domestically and internationally for integrated self-lubricating spherical plain bearing is summarized.Finally,future development trends are outlined:focusing on"high precision and damage-free"as core objectives,and performing multi-objective optimization of forming processes through iterative optimization algorithms to ensure normal operation under extreme conditions such as high temperatures and corrosion.This involves developing novel forming processes by integrating advanced technologies like 3D printing.

Abstract:This paper proposes a method for predicting the service life of wheel bearings under multi-stage complex loads,which is difficult to predict accurately in actual service.Firstly,considering the effect of bending moment,the proposed static model of the wheel bearing is constructed,and the Newton-Raphson iterative algorithm combined with the block method is used to solve the internal contact load of the bearing and resolve the variation law of the contact load in each contact area under different working conditions;Secondly,with reference to the mechanical industry standard JB/T 13353-2017,this study develops a typical load spectrum for durability assessment.Based on the modified L-P theory,the bearing life under this typical load spectrum is determined.Furthermore,to account for the effects of load sequence and interaction present in multi-stage loading,a nonlinear fatigue cumulative damage model is introduced.Finally,the differences between the linear and non-linear damage accumulation models are compared,and the accuracy of the prediction results and the rationality of the method are verified through durability tests.

Abstract:The corrosion resistance of GCr15 bearing steel,a critical material for bearings,is a key determinant of equipment service life.This study investigated the effect of static pressure during ultrasonic rolling extrusion on the corrosion resistance of GCr15 steel.Electrochemical tests and microstructural characterization of samples processed under different static pressures revealed that as the static pressure increased,the linear polarization resistance rose,the corrosion current density decreased,and both the impedance modulus and charge transfer resistance increased,collectively indicating enhanced corrosion resistance.Microstructural analysis demonstrated that the passivation film formed at 200 N primarily consisted of Fe hydroxide and Fe2O3,whereas at 500 N,it was dominated by Fe2O3 and Fe3O4.Furthermore,the thickness and density of the passivation film increased significantly with increasing static pressure.The comprehensive results confirm that ultrasonic rolling extrusion treatment effectively improves the corrosion resistance of GCr15 steel,with the sample treated at 500 N static pressure exhibiting the optimal performance.

Abstract:This study aimed at the problem of bearing electrical corrosion caused by high-frequency alternating electric field such as new energy vehicles and wind power generation.The ceramic ball bearings and steel ball bearings were used to conduct bearing electrical corrosion tests at different shaft voltage frequencies.The results showed that the current density of ceramic ball bearings increased with the increase of frequency,while the steel ball bearings increased first and then decreased.Under the same voltage and frequency conditions,the average current density of ceramic ball bearings was significantly lower than steel ball bearings.Therefore,ceramic ball bearings have lower temperature rise,lubricant leakage,friction coefficient,vibration and noise.After testing for 5 hours,microscopic analysis showed the degree of bearing parts damage was:outer race＞inner race＞ball.The abrasive wear and a few electric erosion pits were observed on outer race of ceramic ball bearing,while a large number of electric erosion was found on the outer race of the steel ball bearing.Moreover,when the shaft voltage frequency was 50 and 1 000 Hz,corrugated damage was observed on the outer race of steel ball bearing.This result indicated the electrical damage of the bearing was related to the current density.The transient high temperatures generated by electrical discharge can cause the decomposition of martensite in the bearing steel,leading to a reduction in internal stress and hardness,with a more pronounced decrease observed in steel ball bearings.Ceramic ball bearings achieve electrical corrosion protection by reducing current density.However,they cannot completely eliminate electrical erosion under high-frequency shaft voltages.Further research is still required to explore new solutions for reducing shaft current density.

Abstract:This study investigated the contact characteristics of the main bearing in a drive unit of a 12 m-class super-large vertical shaft drilling rig under harsh operating conditions.A finite element model of a 1.9 m-class thrust self-aligning roller bearing was developed,and transient dynamic analysis was performed on the ANSYS Workbench platform.The effects of axial load,rotational speed,curvature radius ratio,and contact angle on the bearing contact characteristics,as well as the influence of shock loads on the rollers and inner ring,were systematically examined.The results show that rotational speed has little influence on the contact characteristics of the bearing,whereas the axial load is approximately linearly correlated with the maximum equivalent stress on the rollers,inner ring,and outer ring.The contact stress along the roller generatrix exhibits a significant edge effect,with a maximum contact stress of 2 179.2 MPa.When the curvature radius ratio is 1.04 and the contact angle is 48°,the uniformity of the contact stress distribution improves significantly,and the maximum contact stress decreases to 1 720 MPa.When the shock load pulse width is reduced from 40 ms to 20 ms,the velocity and acceleration responses of the rollers increase by 3～4 times,while the axial displacement is primarily positively correlated with the pulse amplitude.

Abstract:To investigate the precise thermal characteristics of aero-engine accessory gearbox bearings under oil-jet lubrication and improve the lubrication effectiveness of ball bearings in the accessory gearbox,a high-speed 6209 ball bearing was taken as the research object.A bidirectional coupling model between friction heat generation and flow-field temperature distribution was established to analyze the influence of lubrication and operating parameters on the temperature field.The research shows that the increase of bearing speed and load increases the temperature rise of bearing.The increase of oil supply takes away more heat and increases the churning loss,which offsets the original cooling effect of some lubricating oil.Under given conditions,when the oil supply reaches 1.1 L/min,the lubrication effect of the bearing cannot be significantly improved by increasing the oil supply.When the number of nozzles reaches 3,the cooling efficiency also reaches the critical value.The increase of ambient temperature systematically weakens the heat dissipation capacity,resulting in the continuous increase of the temperature of the inner and outer rings of the bearing.

Abstract:To investigate the influence of service conditions on the dynamic response and friction torque of slewing bearings-and to provide a reference for structural optimization and condition-adaptive design:a three-row roller slewing bearing was taken as the research object.A structural and contact mechanics model was established,and simulations were conducted based on a seven-stage service load spectrum(including no-load,high-speed and heavy-load scenarios,etc.).The accuracy of the multibody dynamics model was verified,and the dynamic responses and friction torque evolution of each row of rollers were analyzed.The results show that the maximum error of model validation is 3.19％,meeting the precision requirements.The upper thrust rollers exhibit more stable angular velocity under larger contact loads,the middle radial rollers show intense angular velocity fluctuations due to the absence of a cage,and the lower thrust rollers are prone to skidding due to clearance.The friction torque changes in a"stepped"periodic manner,peaking under high-speed and heavy-load conditions.The upper row of rollers contributes 61.77％of the total friction torque,with rotational speed and load having significant effects on torque.

Abstract:To address the problem of low accuracy caused by sample imbalance in the fault identification of rolling bearings,a fault identification method combining Denoising Diffusion Implicit Model(DDIM)and Swin Transformer(SwinT)is proposed.Firstly,the collected raw vibration signals of rolling bearings were processed using a fast continuous wavelet transform(FCWT)to reconstruct them into two-dimensional time-frequency images.Then,using DDIM,the original imbalanced dataset was augmented to construct a balanced dataset with evenly distributed fault sample categories.Finally,the balanced dataset was applied to the training process of the SwinT model,thereby enabling accurate diagnosis of multiple fault types in rolling bearings.The engineering examples show that the use of DDIM can effectively solve the problem of unbalanced fault samples;at the same time,comparing with other identification models,the SwinT model has a superior bearing fault identification capability.The research results provide a new way for the improvement of rolling bearing fault identification technology under sample imbalance conditions.

Abstract:To reveal the influence of hardness on the wear evolution law of 8Cr4Mo4V bearing steel under high-temperature conditions,8Cr4Mo4V bearing steel samples with different room-temperature hardness were prepared by adjusting the tempering temperature.Friction and wear tests were conducted at 25 ℃,150 ℃,and 300 ℃ under a load of 10 N and a sliding speed of 0.5 m/s.The evolution of wear mechanisms was analyzed by combining friction coefficient measurement,wear morphology observation,and energy spectrum analysis(EDS)characterization.The results show that at 25 ℃,the wear mechanism is dominated by abrasive wear.With the decrease in hardness,the wear resistance of the worn surface decreases with the occurrence of slight material transfer,and the wear mechanism transforms from single abrasive wear to abrasive-adhesive wear,and finally to severe abrasive-adhesive wear.At 150 ℃,the wear mechanism is similar to that at 25 ℃;however,high temperature causes slight softening of the bearing steel surface and a decrease in contact stress,resulting in a lower wear degree.The wear mechanism evolves from mild abrasive wear to mild abrasive-adhesive composite wear.At 300 ℃,the high-hardness sample exhibits contact-concentrated abrasive wear due to contact stress concentration,with wear concentrated in the central part of the contact area.The low-hardness sample undergoes intensified wear,leading to significant material adhesion on the surface,which forms a metal oxide layer through high-temperature oxidation.Its wear mechanism transforms into severe abrasive-adhesive-high temperature oxidative composite wear,where the metal oxide layer plays a key role in reducing friction and wear.

Abstract:To accurately characterize urban passenger vehicle driving patterns and address limitations in traditional driving scenario studies—such as limited sample sizes,poor clustering stability,and the omission of low-probability events during scenario synthesis—a big data-driven method for constructing driving scenarios is proposed.Using one year of OBD data from 200 passenger vehicles in Xi'an,a sample repository was built through data preprocessing and short-trip segmentation.Principal Component Analysis(PCA)was employed to reduce dimensionality to 16 feature parameters.The K-means++algorithm enhances clustering stability and accuracy.Markov Chain Monte Carlo(MCMC)optimizes cycle synthesis while preserving low-probability events.Results show the constructed candidate cycles exhibit an average relative error of 3.63%compared to raw data,significantly outperforming traditional methods:cluster-splicing(4.80%)the Markov chain method(5.60%),and standard driving cycles CLTC-P(8.74%)and WLTC(22.70%).

Abstract:This study aims to explore the regulatory mechanism and repair effect of selenium on the physiological response of alfalfa(Medicago sativa)under the stress of polypropylene nanoplastic.It provides a theoretical basis for the phytoremediation of microplastic-contaminated soil.A pot experiment was conducted.An interaction model was constructed with PP-NPs(100 nm,1%)and soil selenium mass ratio gradients(0,0.4,0.8,1.2,1.6 mg·kg-1).The responses of growth indices,chlorophyll content,photosynthetic parameters,nutritional quality,and root parameters of alfalfa(75 d growth cycle)were systematically evaluated.The results show that the addition of PP-NPs significantly inhibits the plant height,aboveground biomass,net photosynthetic rate,stomatal conductance,and contents of chlorophyll a and chlorophyll b of alfalfa(P<0.05),which are decreased by 9.8%,3.3%,35.4%,49.5%,11.3%,and 10.7%,respectively.The addition of selenium can alleviate the toxic effects of PP-NPs and significantly increase the net photosynthetic rate and chlorophyll content of alfalfa(P<0.05).A membership function evaluation system based on principal component analysis is established using 5 indicators,including aboveground biomass,dry matter content,crude protein content,acid detergent fiber content,and neutral detergent fiber content.It is quantitatively concluded that the 1.2 mg·kg-1 selenium treatment performed best in comprehensive indicators.The results of the study show that selenium improves the stress resistance and productivity of alfalfa under PP-NPs pollution through photosynthetic gain and root architecture remodeling.This provides a new technical pathway for high-quality forage production in microplastic-contaminated agricultural areas.

Abstract:Two types of shear walls with variable stiffness connections using limited-slip bolts and blocking frames were designed.Quasi-static compression-shear tests were conducted to investigate the influence of this connection method on seismic performance.The results show that both variable stiffness connection designs effectively achieve segmented working mechanisms.The hysteretic curves exhibit spindle shapes,and demonstrate excellent overall seismic performance.Compared to traditional corrugated steel plate shear walls,the variable stiffness shear walls with limited-slip bolts and blocking frames show a 47%increase in bearing capacity at an inter-story drift angle of 2%.The variable stiffness design using only blocking frames displays a hilly-shaped"double peak"phenomenon with secondary bearing capacity recovery after gradual degradation,resulting in more stable energy dissipation performance.At an inter-story drift angle of 4%,the secondary bearing capacity increases by 26%.

Abstract:To mitigate the formation of brittle Ti-Fe intermetallic compounds,resistance spot welding of 2 mm thick titanium and 1 mm thick Q235 low-carbon steel was conducted using a 0.1 mm thick composite interlayer consisting of niobium and C7701 white copper foil.The effects of welding current and welding time on nugget diameter and mechanical properties of the joints were investigated,along with microstructural analysis.Results indicated that when nuggets were separated on both sides,a layer comprising FeNb intermetallic compounds and(Nb)solid solution formed between the steel-side nugget and the residual Nb layer.In contrast,a single mixed nugget consisting of TiFe and α-Ti was observed when the joint nugget was unified.With increasing welding current and duration,the nugget diameter expanded,while the shear load first increased and then decreased.The maximum shear load,approximately 7.995 kN,was obtained at 7 kA and 300 ms.

Abstract:To address the dual demand for thermal safety and energy efficiency optimization of power batteries in new energy vehicles,a 23 Ah prismatic lithium iron phosphate(LiFePO4)cell was selected as the research object.A titanium dioxide nanofluid pulsating heat pipe(PHP)was employed as the core cooling device,and a comprehensive thermal management system based on temperature-graded regulation and an economy-oriented coupling criterion was proposed and implemented.This system ensures battery thermal safety by dynamically adjusting fan speed according to real-time temperature monitoring,while introducing an economy criterion once the temperature requirement is satisfied,thereby achieving an optimal balance between cooling performance and energy consumption.Relying on a self-developed experimental platform,tests were carried out on both single cells and battery modules under different ambient temperatures(15℃,25℃,and 35℃).To simulate low-power operating conditions of electric vehicles,constant discharge rates of 0.5 C,1 C,and 1.5 C as well as variable-rate cycles were adopted.The results show that the proposed system can maintain the maximum temperature below 45℃,with the economy index reaching up to 91.7%,thereby demonstrating significant energy-saving advantages while ensuring thermal safety under low-power operating conditions.

Abstract:Establishing an accurate mathematical model of the load object for a gas-steam combined cycle unit is a crucial prerequisite for improving the performance of its load control system.To address the limitations of traditional identification methods in terms of accuracy and convergence speed,this paper proposes a model identification approach based on an improved sand cat swarm optimization(ISCSO)algorithm.First,the initial population is enhanced using Logistic chaotic mapping.The sensitivity parameter is modified from linear to cosine-based variation.Additionally,a differential evolution mutation mechanism and Gaussian perturbation method are introduced to improve optimization efficiency and effectively avoid local optima.Then,the ISCSO algorithm is employed to optimize the model parameters and obtain their optimal values.Finally,model identification results from the ISCSO and SCSO algorithms are compared and validated using data obtained from an open-loop step experiment at the 312.06 MW load point of the gas-steam combined cycle unit.The effectiveness of the improvement strategies in the algorithm is validated through ablation experiments.The results demonstrate that the proposed algorithm establishes a more accurate load model compared to benchmark algorithms.The ISCSO-identified model achieves the lowest mean absolute percentage error(MAPE)and root mean square error(RMSE),exhibiting superior convergence performance.This work provides a new methodology for model identification.

Abstract:This study systematically investigates the forming processes and microstructural evolution of high-Nb TiAl alloys and their carbide-reinforced composites.It focuses on analyzing the effects of ball-milled powder blending and hot-press sintering parameters on microstructure,while revealing the variation patterns of oxygen mass fraction during forming process.Results indicate that in the sintering temperature range of 1 350～1 450℃,the 1 425℃-30 MPa-20 min process yields a dense TiAl alloy with uniform fully lamellar microstructure.Ball milling represents the primary stage contributing to oxygen mass fraction increase.Glove box purging proves more effective than vacuum pump purging in reducing oxygen mass fraction.The high oxygen mass fraction(3.63%)in nano-TiC powder causes oxygen mass fraction in sintered specimens to increase proportionally with powder loading.Compared to the 150 r/min-8 h mixing process,the 200 r/min-8 h parameters significantly improve the dispersion uniformity of nano-TiC particles and suppress carbide agglomeration in TiAl-based composites by enhancing powder fragmentation and specific surface area.

Abstract:For a mixed-order heterogeneous multi-agent system with cooperative-competitive interactions,whose topology exhibits a directed weakly connected characteristic,this paper designs a dynamic event-triggered consensus control scheme.By integrating it with a pinning control approach,the system achieves exponential convergence and realizes the Couple-Group consensus.Firstly,by incorporating dynamically varying thresholds into event-triggering conditions,adaptive regulation is achieved.Compared with conventional static event-triggered control frameworks,this modification prevents unnecessary controller activations while reducing communication resource consumption.Subsequently,sufficient conditions for consensus attainment are derived through Lyapunov stability theory,accompanied by corresponding pinning strategies.Simultaneously,Zeno behavior is strictly excluded.Numerical simulations ultimately validate the accuracy and feasibility of the proposed dynamic event-triggered control strategy.