The S38C railway axle undergoes induction hardening,resulting in a gradient-distributed microstructure and mechanical properties.The accurate identification of gradient-distributed plastic parameters for the S38C axle...The S38C railway axle undergoes induction hardening,resulting in a gradient-distributed microstructure and mechanical properties.The accurate identification of gradient-distributed plastic parameters for the S38C axle remains a challenging task.To tackle this challenge,the present study proposes a novel approach for identifying the gradient-distributed plastic parameters for the S38C axle by integrating nano-indentation techniques with the machine learning method.Firstly,nano-indentation tests are conducted along the radial direction of the S38C axle to obtain the gradient-distributed load-displacement curves,nano-hardness,and elastic modulus.Subsequently,the dimensionless analysis is performed to obtain the representative stress,strain,and yield stress from load-displacement curves.These parameters are then incorporated into the machine learning method as physical information to identify the gradient-distributed plastic parameters of the S38C axle.The results indicate that the proposed method based on the physics-informed neural network and multi-fidelity neural network successfully identifies the gradient-distributed plastic parameters of the S38C axles and demonstrates superior prediction accuracy and generalization compared with the purely data-driven machine learning method.展开更多
Statistical distribution of residual fatigue life(RFL)of railway axles under given loading was computed using the Monte Carlo method by considering random variation of the selected input parameters.Experimental data f...Statistical distribution of residual fatigue life(RFL)of railway axles under given loading was computed using the Monte Carlo method by considering random variation of the selected input parameters.Experimental data for the EA4T railway axle steel,the loading spectrum,the press fit loading and the residual stress induced by surface hardening were considered in the crack propagation simulations.Usually,the material properties measured by tensile tests are considered to be the most informative source of material data.Under fatigue loading,however,the crack growth rates near the threshold are the most critical data.Two important influencing factors on these crack growth rates are presented:first,the air humidity and,second,the near-surface residual stress.The typical variation of these parameters in operation may change the RFL by one or two orders of magnitude.Experimentally obtained crack growth thresholds and residual stress profiles are highly affected by the used methodology.Therefore,the obtained input data may be located anywhere within a large scatter,while the experimenters are completely unaware of it.This can lead to dangerously non-conservative situations,e.g.when the thresholds are measured in a laboratory under humid air conditions and then applied to predictions of RFLs of axles operated in winter in low air humidity.This is significant for the topic of inspection interval optimisation.The results of experiments done on real 1:1 railway axles were close to the most frequent value found in the histogram of the numerically computed RFLs.展开更多
Axle box bearings are critical components of high-speed trains.Localized defects,such as pitting and spalling,on raceways or rollers pose significant threats to the operational safety of railway vehicles.In this work,...Axle box bearings are critical components of high-speed trains.Localized defects,such as pitting and spalling,on raceways or rollers pose significant threats to the operational safety of railway vehicles.In this work,a novel bearing-flexible axle boxvehicle coupling model is established to explore the vibration characteristics of axle box bearings with irregular localized defects.First,based on the contact and kinematic relationship between rollers and raceways,the three-dimensional(3D)bearing force elements are analyzed and formulated.Second,the established model and a flexible axle box are integrated into the vehicle,and the responses of the normal and faulty bearings under the combined excitations of wheel roughness and track irregularities are simulated.Third,the simulation results are verified through a rolling-vibrating test bench for full-scale wheelsets of high-speed trains.The comparisons of the fault-induced repetitive transients in the time-domain and the fault characteristic frequencies in the envelope spectra demonstrate the efficiency of the proposed model.Finally,based on the flexible axle box model,a sensitivity analysis of the accelerometer placements to the bearing faults is carried out,and the optimal one is identified based on both the time-domain and frequency-domain signal-to-noise ratios(SNRs)for engineering applications.展开更多
Purpose–To address the encapsulation challenge of fiber Bragg grating(FBG)sensors in complex railway environments,this paper designs a clip-on composite sensor enabling installation-friendly deployment and long-term ...Purpose–To address the encapsulation challenge of fiber Bragg grating(FBG)sensors in complex railway environments,this paper designs a clip-on composite sensor enabling installation-friendly deployment and long-term axle counting system monitoring.Design/methodology/approach–Wheel–rail mechanical behavior was simulated via finite element analysis(FEA)to determine optimal sensor placement.A clip-on composite sensor was subsequently engineered.Stress transduction efficacy was validated through FEA quantification of stress responses at the axle counter location.Findings–The proposed FBG axle counter integrates temperature compensation and anti-detachment monitoring as well as advantages such as simplified installation with minimal maintenance and sustained operational reliability.It effectively transmits stress,yielding a measured strain of 39μe under static loading conditions without sensitivity-enhancing elements.Originality/value–This study performs FEA of wheel-rail stress distribution and engineers the dual-slot composite sensor,FEAwas conducted to quantify the stress magnitude at the axle sensor position of the dual-slot composite sensor.Additionally,FEA was performed on sensors with different structural configurations,including adjustments to the axle sensor position,number of slots and axle position.The results confirmed that the designed composite sensor exhibits superior stress transfer characteristics.展开更多
In this paper,the front axle of a certain model is taken as the research object,and the stress and deformation of the frontaxle under three typical working conditions are analyzed by finite element technology.Based on...In this paper,the front axle of a certain model is taken as the research object,and the stress and deformation of the frontaxle under three typical working conditions are analyzed by finite element technology.Based on the simulation results,the 3D model of the front axle was optimized,and the finite element analysis of the optimized structure of the front axle under three typical working conditions was carried out to verify the correctness of the model.Finally,the fatigue tool module of ANSYS Workbench was used to analyze the fatigue life of the front axle under the optimized emergency conditions,and the feasibility of the model was verified.The analysis data shows that the design of the front axle components still has a lot of potential for lightweighting,and the weight of the front axle can be reduced by 6.73%through optimization,and the performance of the front axle can also meet the needs of use.The research conclusionhas a certain reference value for the lightweight design of automobile front axle.展开更多
Heavy-duty freight railway axles are no less important than those of passenger trains,owing to the potentially catastrophic results caused by the derailment of trains carrying hazardous substances.Intrinsic and extrin...Heavy-duty freight railway axles are no less important than those of passenger trains,owing to the potentially catastrophic results caused by the derailment of trains carrying hazardous substances.Intrinsic and extrinsic imperfections challenge classical design theories built based on the safe life concept,and damage tolerance assessment becomes vital for the safety and reliability of long-term serviced railway axles,as pits and scratches are common defects for heavy-duty railway axles.In this work,four-point rotating bending fatigue tests of AAR-CM railway axle steel specimens with semicircular and circumferential groove notches are conducted.The fatigue limit of the semicircular notched specimens was evaluated based on fracture mechanics theory,in which non-conservative results are obtained by the El Haddad model and the S–N curves of circumferential groove notched specimens are correlated by the theory of critical distance(TCD).展开更多
Axle box bearings serve as crucial components within the transmission system of high-speed trains.Their failure can directly impact the operational safety of these trains.Accurately determining the dynamic load experi...Axle box bearings serve as crucial components within the transmission system of high-speed trains.Their failure can directly impact the operational safety of these trains.Accurately determining the dynamic load experienced by bearings during the operation of high-speed trains can provide valuable boundary inputs for the study of bearing fatigue life and service performance,thereby holding significant engineering implications.In this study,we propose a high-speed train axle box bearing load estimation method(FMCC-DKF).This method is founded on the Kalman filtering technique of the Maximum Correntropy Criterion(MCC)and employs dummy measurement technology to enhance the stability of estimated loads.We develop a kernel size update algorithm to address the challenges associated with obtaining the key parameter,kernel size of MCC.Comparative analysis of the vertical and lateral loads of the axle box bearing obtained using FMCC-DKF,DKF,and AMCC-DKF,under both measurement noise-free and non-Gaussian noise conditions,is conducted to demonstrate the superiority of the proposed estimation method.The results indicate that the proposed FMCC-DKF method exhibits high estimation accuracy under both measurement noise-free and non-Gaussian noise interference,and maintains its high estimation accuracy despite changes in train speed.The proposed load estimation method demonstrates reliable performance within the low-frequency domain below 70 Hz.展开更多
By using the finite element method （FEM）, we comprehensively analyzed the fields of temperature, organization, and stress in 35CrMo train axles during the quenching process is conducted, and experimentally studied t...By using the finite element method （FEM）, we comprehensively analyzed the fields of temperature, organization, and stress in 35CrMo train axles during the quenching process is conducted, and experimentally studied the formation and evolution of inner stresses in axles during the quenching process. The results show that in the quenching process, stresses on the axle surface change from tensile to compressive gradually, while stresses in the axle core change from compressive to tensile gradually. Heat stresses and the amount of martensitic transformation are all increased with the increase of cooling rate. As a result, the maximmn instantaneous stresses in the axle are increased greatly when the cooling rate is increased with brine quenching. Large instantaneous tensile stress in the axle core with brine quenching is very likely to cause quench cracking and should be avoided.展开更多
Half axle gears is produced by precision forging popularly because of the advantages in minimum machining allowances, lower material consumption and good service properties. But the forming quality of precision forgin...Half axle gears is produced by precision forging popularly because of the advantages in minimum machining allowances, lower material consumption and good service properties. But the forming quality of precision forging is difficult to control. Many simulations and analysis of precision forging process were taken by previous researchers. But no concrete method is proposed to evaluate and optimize the forming quality of half axel gears. The primary purpose of this work is improving the forming quality of half axel gears by analyzing and optimizing the affected factors of forming quality. The enclosed-die warm forging process of half axle gears was developed, and a new type of die-set used on double action hydraulic press was brought forward. The main influential factors of precision forming quality were analyzed after the forming process had been simulated by using finite element method（FEM）. These factors include die structure, web thickness and web position. A method used to evaluate the forming quality was established, which investigated the maximal forming load, the metal filling rate and the material damage factor. The FEM simulations of half axle gears precision forging were evaluated by this method. The results show that the best forming quality can be achieved when the punches were added with bosses, the web located at the middle plant of the gear, and the web thickness was 30 percent of the inner hole diameter. Verification experiments taking the above optimized parameters were performed on a 7.8 MN double action hydraulic press. The trial products were formed well. And their geometric precision meets the demand. The verification result shows that the optimization of the influential factors, according to the simulations and the evaluation method, can improve the forming quality. The new structure of precision forging die-set and the new evaluation method guarantee a high forming quality ofhalfaxel gears.展开更多
According to the rules of UIC515-3,the service loads of the axles are defined,which include some different loads cases as follows:the static loads;the impact loads resulted from running through the rail joints and une...According to the rules of UIC515-3,the service loads of the axles are defined,which include some different loads cases as follows:the static loads;the impact loads resulted from running through the rail joints and unevenness rails;the loads through curves and from braking.Through the calculating and analysis,the stress distribution of the hollow axles is obtained for 200 km/h high speed motor trains used in China.At the same time,the fatigue crack growth of hollow axles is studied,and the initial surface cracks of 2 mm depth caused by hard objects strike or the other causes are discussed.On the basis of the linear elastic fracture mechanics theory,the stress intensity factor of the crack of the geometry transition outside the wheel seat is also studied.Associated with fatigue crack propagation equation and the corresponding crack propagation threshold,the crack propagation characteristics under different shapes are calculated.Then the running distances are educed with different shapes propagating to the critical length,and the estimation of the residual lives about hollow axles which are the reference values of examine and repair limit of the hollow axle is given.展开更多
Fatigue fracture is the major threat to the railway axle, which can be avoided or delayed by surface strengthening. In this study, a low-carbon alloy axle steel with two states was treated by surface induction hardeni...Fatigue fracture is the major threat to the railway axle, which can be avoided or delayed by surface strengthening. In this study, a low-carbon alloy axle steel with two states was treated by surface induction hardening and shot peening, respectively, to reveal the mechanism of fatigue property improvement by microstructure characterization, microhardness measurement, residual stress analysis, roughness measurement, and rotary bending fatigue tests. The results indicate that both quenching and tempering treatment can effectively improve the fatigue properties of the modified axle steel. In addition, induction hardening can create an ideal hardened layer on the sample surface by phase transformation from the microstructure of ferrite and pearlite to martensite. By comparison, shot peening can modify the microstructure in surface layer by surface severe plastic deformation introducing a large number of dislocation and even cause grain refinement. Both induction hardening and shot peening create compressive residual stress into the surface layer of axle steel sample, which can effectively reduce the stress level applied to the metal surface during the rotary bending fatigue tests. On the whole, the contribution of induction hardening to the fatigue life of axle steel sample is better than that of the shot peening, and induction hardening shows obvious advantages in improving the fatigue life of axle steel.展开更多
This study investigated the fretting wear and fatigue of full-scale railway axles.Fatigue tests were conducted on full-scale railway axles,and the fretting wear and fretting fatigue in the fretted zone of the railway ...This study investigated the fretting wear and fatigue of full-scale railway axles.Fatigue tests were conducted on full-scale railway axles,and the fretting wear and fretting fatigue in the fretted zone of the railway axles were analysed.Three-dimensional finite element models were established based on the experimental results.Then,multi-axial fatigue parameters and a linear elastic fracture mechanics-based approach were used to investigate the fretting fatigue crack initiation and propagation,respectively,in which the role of the fretting wear was taken into account.The experimental and simulated results showed that the fretted zone could be divided into zones I-III according to the surface damage morphologies.Fretting wear alleviated the stress concentration near the wheel seat edge and resulted in a new stress concentration near the worn/unworn boundary in zone II,which greatly promoted the fretting crack initiation at the inner side of the fretted zone.Meanwhile,the stress concentration also increased the equivalent stress intensity factor range DKeq below the mating surface,and thus promoted the propagation of fretting fatigue crack.Based on these findings,the effect of the stress redistribution resulting from fretting wear is suggested to be taken into account when evaluating the fretting fatigue in railway axles.展开更多
Because of the wicked service environment of the high speed train,it is possible that the hollow axle of the train may encounter the foreign object damage and form a sharp notch.Under the fatigue loading a crack can i...Because of the wicked service environment of the high speed train,it is possible that the hollow axle of the train may encounter the foreign object damage and form a sharp notch.Under the fatigue loading a crack can initiate from the notch and propagate to failure.It is noted that the stress intensity factor is the control parameter of the crack propagating,for the purpose of getting the more exact propagation characteristics,the stress intensity factor is studied mainly.The service loads of hollow axles are defined,and the stress distribution of hollow axles is obtained according to the load spectrum.The semi-ellipse crack configuration is defined with three parameters:the aspect ratio,the relative depth and the relative location along the crack front.Quarter point 20-node isoparametric degenerate singular elements are used for the region near the crack tip.The finite element model of crack extension of hollow axle is created,and the crack front is dispersed which can realize orthogonal extension.Based on this the stress intensity factors of crack front were calculated,and the distribution rules of the stress intensity factors of different initial crack shapes are obtained.The conclusions are compared with that of the analytic method and they agree with each other very well,and the calculating results show that there is a close relationship between the stress intensity factor and the initial crack shape.For a round crack the stress intensity factor at the surface point increases faster than the one at the center point with the crock propagation.However,for a narrow crack,the results are in contrast with that of a round one.So,all the cracks with different shapes propagate toward to a similar shape,and they grow at this shape to end.The study may contribute to the crack propagate characteristics research.展开更多
The wheel diameter difference would worsen the dynamic performance and affect the safety of the rail vehicle.Therefore,it is necessary to detect wheel diameter difference while the train is operating.However,several e...The wheel diameter difference would worsen the dynamic performance and affect the safety of the rail vehicle.Therefore,it is necessary to detect wheel diameter difference while the train is operating.However,several existing detection methods can’t accurately detect and diagnose the wheel diameter difference under highspeed running environment.In this study,a new method of detecting wheel diameter difference was proposed for high speed rail vehicle.The wheel diameter difference would be diagnosed by the amplitude and frequency of vibration impact on the axle box.Firstly,the dynamic model with varying wheel diameters was established in SIMPACK,and LMA tread was used in high-speed rail vehicles.Then,the simulation results of rail vehicle dynamic performance were compared under different wheel diameter differences.After that,the relationship between axle box vibration and wheel diameter difference was used to demonstrate the feasibility of this detection technology.Finally,comparing and analyzing the simulation results of vibration obtained by matching treads with different wheel diameters,it shows that by increasing the wheel diameter difference,the longitudinal and lateral impacts on axle boxes increase asymmetrically,and the amplitude and the frequency become more evident.Therefore,this paper presents a technical scheme of online measuring wheel diameter difference by monitoring the vibration of the axle box.展开更多
The microstructure,precipitates and properties of 25CrNiMoV(DZ2)steel for high-speed railway axles with different Nb contents were investigated by means of optical microscopy,scanning electron microscopy,electron back...The microstructure,precipitates and properties of 25CrNiMoV(DZ2)steel for high-speed railway axles with different Nb contents were investigated by means of optical microscopy,scanning electron microscopy,electron back-scattering diffraction,transmission electron microscopy and physicochemical phase analysis.The results show that the grain size of the original austenite of the test steels decreases from 20.5 to 14.2 and 10.8μm after adding 0.026 and 0.039 wt.%Nb to a 25CrNiMoV steel,respectively.Moreover,the block width of the tempered martensite in the test steels is refined from 1.91 to 1.72 and 1.60µm,respectively.MC-type precipitates in 25CrNiMoV steel are mainly VC,while(Nb,V)C gradually precipitates when Nb is microalloyed,and the amount of precipitates increases with increasing Nb content.Through strengthening mechanism analysis,it is found that grain refinement strengthening is the primary way to increase the strength.The improvement in the yield strength with increasing Nb content is attributed to a significant increase in precipitation strengthening,grain refinement strengthening and dislocation strengthening.展开更多
基金supported by the National Key Research and Development Plan(Grant No.2022YFB3401901)the National Natural Science Foundation of China(Grant Nos.12192210,12192214,12072295,and 12222209)+1 种基金Independent Project of State Key Laboratory of Rail Transit Vehicle System(Grant No.2023TPL-T03)Fundamental Research Funds for the Central Universities(Grant No.2682023CG004).
文摘The S38C railway axle undergoes induction hardening,resulting in a gradient-distributed microstructure and mechanical properties.The accurate identification of gradient-distributed plastic parameters for the S38C axle remains a challenging task.To tackle this challenge,the present study proposes a novel approach for identifying the gradient-distributed plastic parameters for the S38C axle by integrating nano-indentation techniques with the machine learning method.Firstly,nano-indentation tests are conducted along the radial direction of the S38C axle to obtain the gradient-distributed load-displacement curves,nano-hardness,and elastic modulus.Subsequently,the dimensionless analysis is performed to obtain the representative stress,strain,and yield stress from load-displacement curves.These parameters are then incorporated into the machine learning method as physical information to identify the gradient-distributed plastic parameters of the S38C axle.The results indicate that the proposed method based on the physics-informed neural network and multi-fidelity neural network successfully identifies the gradient-distributed plastic parameters of the S38C axles and demonstrates superior prediction accuracy and generalization compared with the purely data-driven machine learning method.
基金financially supported by the Czech Science Foundation in the frame of the project No.22-28283Sby the Technology Agency of the Czech Republic through the project No.CK03000060.
文摘Statistical distribution of residual fatigue life(RFL)of railway axles under given loading was computed using the Monte Carlo method by considering random variation of the selected input parameters.Experimental data for the EA4T railway axle steel,the loading spectrum,the press fit loading and the residual stress induced by surface hardening were considered in the crack propagation simulations.Usually,the material properties measured by tensile tests are considered to be the most informative source of material data.Under fatigue loading,however,the crack growth rates near the threshold are the most critical data.Two important influencing factors on these crack growth rates are presented:first,the air humidity and,second,the near-surface residual stress.The typical variation of these parameters in operation may change the RFL by one or two orders of magnitude.Experimentally obtained crack growth thresholds and residual stress profiles are highly affected by the used methodology.Therefore,the obtained input data may be located anywhere within a large scatter,while the experimenters are completely unaware of it.This can lead to dangerously non-conservative situations,e.g.when the thresholds are measured in a laboratory under humid air conditions and then applied to predictions of RFLs of axles operated in winter in low air humidity.This is significant for the topic of inspection interval optimisation.The results of experiments done on real 1:1 railway axles were close to the most frequent value found in the histogram of the numerically computed RFLs.
基金supported by the National Natural Science Foundation of China(Nos.12372056,12032017,12393783)the S&T Program of Hebei of China(No.24465001D)。
文摘Axle box bearings are critical components of high-speed trains.Localized defects,such as pitting and spalling,on raceways or rollers pose significant threats to the operational safety of railway vehicles.In this work,a novel bearing-flexible axle boxvehicle coupling model is established to explore the vibration characteristics of axle box bearings with irregular localized defects.First,based on the contact and kinematic relationship between rollers and raceways,the three-dimensional(3D)bearing force elements are analyzed and formulated.Second,the established model and a flexible axle box are integrated into the vehicle,and the responses of the normal and faulty bearings under the combined excitations of wheel roughness and track irregularities are simulated.Third,the simulation results are verified through a rolling-vibrating test bench for full-scale wheelsets of high-speed trains.The comparisons of the fault-induced repetitive transients in the time-domain and the fault characteristic frequencies in the envelope spectra demonstrate the efficiency of the proposed model.Finally,based on the flexible axle box model,a sensitivity analysis of the accelerometer placements to the bearing faults is carried out,and the optimal one is identified based on both the time-domain and frequency-domain signal-to-noise ratios(SNRs)for engineering applications.
文摘Purpose–To address the encapsulation challenge of fiber Bragg grating(FBG)sensors in complex railway environments,this paper designs a clip-on composite sensor enabling installation-friendly deployment and long-term axle counting system monitoring.Design/methodology/approach–Wheel–rail mechanical behavior was simulated via finite element analysis(FEA)to determine optimal sensor placement.A clip-on composite sensor was subsequently engineered.Stress transduction efficacy was validated through FEA quantification of stress responses at the axle counter location.Findings–The proposed FBG axle counter integrates temperature compensation and anti-detachment monitoring as well as advantages such as simplified installation with minimal maintenance and sustained operational reliability.It effectively transmits stress,yielding a measured strain of 39μe under static loading conditions without sensitivity-enhancing elements.Originality/value–This study performs FEA of wheel-rail stress distribution and engineers the dual-slot composite sensor,FEAwas conducted to quantify the stress magnitude at the axle sensor position of the dual-slot composite sensor.Additionally,FEA was performed on sensors with different structural configurations,including adjustments to the axle sensor position,number of slots and axle position.The results confirmed that the designed composite sensor exhibits superior stress transfer characteristics.
文摘In this paper,the front axle of a certain model is taken as the research object,and the stress and deformation of the frontaxle under three typical working conditions are analyzed by finite element technology.Based on the simulation results,the 3D model of the front axle was optimized,and the finite element analysis of the optimized structure of the front axle under three typical working conditions was carried out to verify the correctness of the model.Finally,the fatigue tool module of ANSYS Workbench was used to analyze the fatigue life of the front axle under the optimized emergency conditions,and the feasibility of the model was verified.The analysis data shows that the design of the front axle components still has a lot of potential for lightweighting,and the weight of the front axle can be reduced by 6.73%through optimization,and the performance of the front axle can also meet the needs of use.The research conclusionhas a certain reference value for the lightweight design of automobile front axle.
基金Supported by National Natural Science Foundation of China(Grant No.12232004)Guangdong Provincial Basic and Applied Basic Research Foundation(Grant No.2022A1515140111)+1 种基金Anhui Provincial Science and Technology Projects(Grant No.JB24075)Sichuan Provincial Science and Technology Program(Grant Nos.2024NSFSC2020,2023YFG0234)。
文摘Heavy-duty freight railway axles are no less important than those of passenger trains,owing to the potentially catastrophic results caused by the derailment of trains carrying hazardous substances.Intrinsic and extrinsic imperfections challenge classical design theories built based on the safe life concept,and damage tolerance assessment becomes vital for the safety and reliability of long-term serviced railway axles,as pits and scratches are common defects for heavy-duty railway axles.In this work,four-point rotating bending fatigue tests of AAR-CM railway axle steel specimens with semicircular and circumferential groove notches are conducted.The fatigue limit of the semicircular notched specimens was evaluated based on fracture mechanics theory,in which non-conservative results are obtained by the El Haddad model and the S–N curves of circumferential groove notched specimens are correlated by the theory of critical distance(TCD).
基金National Key R&D Program of China(Grant numbers 2022YFB4301201-11,2022YFB4301203-05)National Natural Science Foundation of China(Grant number 52202464).
文摘Axle box bearings serve as crucial components within the transmission system of high-speed trains.Their failure can directly impact the operational safety of these trains.Accurately determining the dynamic load experienced by bearings during the operation of high-speed trains can provide valuable boundary inputs for the study of bearing fatigue life and service performance,thereby holding significant engineering implications.In this study,we propose a high-speed train axle box bearing load estimation method(FMCC-DKF).This method is founded on the Kalman filtering technique of the Maximum Correntropy Criterion(MCC)and employs dummy measurement technology to enhance the stability of estimated loads.We develop a kernel size update algorithm to address the challenges associated with obtaining the key parameter,kernel size of MCC.Comparative analysis of the vertical and lateral loads of the axle box bearing obtained using FMCC-DKF,DKF,and AMCC-DKF,under both measurement noise-free and non-Gaussian noise conditions,is conducted to demonstrate the superiority of the proposed estimation method.The results indicate that the proposed FMCC-DKF method exhibits high estimation accuracy under both measurement noise-free and non-Gaussian noise interference,and maintains its high estimation accuracy despite changes in train speed.The proposed load estimation method demonstrates reliable performance within the low-frequency domain below 70 Hz.
基金Funded by the National Basic Research Program of China(Nos.2010CB731703,2012CB619505)the National Natural Science Foundation of China(Nos.51405520,51327902)
文摘By using the finite element method （FEM）, we comprehensively analyzed the fields of temperature, organization, and stress in 35CrMo train axles during the quenching process is conducted, and experimentally studied the formation and evolution of inner stresses in axles during the quenching process. The results show that in the quenching process, stresses on the axle surface change from tensile to compressive gradually, while stresses in the axle core change from compressive to tensile gradually. Heat stresses and the amount of martensitic transformation are all increased with the increase of cooling rate. As a result, the maximmn instantaneous stresses in the axle are increased greatly when the cooling rate is increased with brine quenching. Large instantaneous tensile stress in the axle core with brine quenching is very likely to cause quench cracking and should be avoided.
基金supported by Chongqing Municipal Science and Technology Committee of China (Grant No. 2005AA3012-4)
文摘Half axle gears is produced by precision forging popularly because of the advantages in minimum machining allowances, lower material consumption and good service properties. But the forming quality of precision forging is difficult to control. Many simulations and analysis of precision forging process were taken by previous researchers. But no concrete method is proposed to evaluate and optimize the forming quality of half axel gears. The primary purpose of this work is improving the forming quality of half axel gears by analyzing and optimizing the affected factors of forming quality. The enclosed-die warm forging process of half axle gears was developed, and a new type of die-set used on double action hydraulic press was brought forward. The main influential factors of precision forming quality were analyzed after the forming process had been simulated by using finite element method（FEM）. These factors include die structure, web thickness and web position. A method used to evaluate the forming quality was established, which investigated the maximal forming load, the metal filling rate and the material damage factor. The FEM simulations of half axle gears precision forging were evaluated by this method. The results show that the best forming quality can be achieved when the punches were added with bosses, the web located at the middle plant of the gear, and the web thickness was 30 percent of the inner hole diameter. Verification experiments taking the above optimized parameters were performed on a 7.8 MN double action hydraulic press. The trial products were formed well. And their geometric precision meets the demand. The verification result shows that the optimization of the influential factors, according to the simulations and the evaluation method, can improve the forming quality. The new structure of precision forging die-set and the new evaluation method guarantee a high forming quality ofhalfaxel gears.
基金National Basic Research and Development Program of China(973 Program,No.2007CB714705).
文摘According to the rules of UIC515-3,the service loads of the axles are defined,which include some different loads cases as follows:the static loads;the impact loads resulted from running through the rail joints and unevenness rails;the loads through curves and from braking.Through the calculating and analysis,the stress distribution of the hollow axles is obtained for 200 km/h high speed motor trains used in China.At the same time,the fatigue crack growth of hollow axles is studied,and the initial surface cracks of 2 mm depth caused by hard objects strike or the other causes are discussed.On the basis of the linear elastic fracture mechanics theory,the stress intensity factor of the crack of the geometry transition outside the wheel seat is also studied.Associated with fatigue crack propagation equation and the corresponding crack propagation threshold,the crack propagation characteristics under different shapes are calculated.Then the running distances are educed with different shapes propagating to the critical length,and the estimation of the residual lives about hollow axles which are the reference values of examine and repair limit of the hollow axle is given.
基金financially supported by the National Key Research and Development Project(No.2017YFB0703004)the National Natural Science Foundation of China(NSFC,No.U1664253)the LiaoNing Revitalization Talents Program(No.XLYC1808027)。
文摘Fatigue fracture is the major threat to the railway axle, which can be avoided or delayed by surface strengthening. In this study, a low-carbon alloy axle steel with two states was treated by surface induction hardening and shot peening, respectively, to reveal the mechanism of fatigue property improvement by microstructure characterization, microhardness measurement, residual stress analysis, roughness measurement, and rotary bending fatigue tests. The results indicate that both quenching and tempering treatment can effectively improve the fatigue properties of the modified axle steel. In addition, induction hardening can create an ideal hardened layer on the sample surface by phase transformation from the microstructure of ferrite and pearlite to martensite. By comparison, shot peening can modify the microstructure in surface layer by surface severe plastic deformation introducing a large number of dislocation and even cause grain refinement. Both induction hardening and shot peening create compressive residual stress into the surface layer of axle steel sample, which can effectively reduce the stress level applied to the metal surface during the rotary bending fatigue tests. On the whole, the contribution of induction hardening to the fatigue life of axle steel sample is better than that of the shot peening, and induction hardening shows obvious advantages in improving the fatigue life of axle steel.
基金the Independent Research Project of the State Key Laboratory of Traction Power(No.2018TPL_Z01)the National Natural Science Foundation of China(No.51375406)the Fundamental Research Funds for the Central Universities(No.2682018CX68).
文摘This study investigated the fretting wear and fatigue of full-scale railway axles.Fatigue tests were conducted on full-scale railway axles,and the fretting wear and fretting fatigue in the fretted zone of the railway axles were analysed.Three-dimensional finite element models were established based on the experimental results.Then,multi-axial fatigue parameters and a linear elastic fracture mechanics-based approach were used to investigate the fretting fatigue crack initiation and propagation,respectively,in which the role of the fretting wear was taken into account.The experimental and simulated results showed that the fretted zone could be divided into zones I-III according to the surface damage morphologies.Fretting wear alleviated the stress concentration near the wheel seat edge and resulted in a new stress concentration near the worn/unworn boundary in zone II,which greatly promoted the fretting crack initiation at the inner side of the fretted zone.Meanwhile,the stress concentration also increased the equivalent stress intensity factor range DKeq below the mating surface,and thus promoted the propagation of fretting fatigue crack.Based on these findings,the effect of the stress redistribution resulting from fretting wear is suggested to be taken into account when evaluating the fretting fatigue in railway axles.
基金supported by National Basic Research and Development Program of China(973 Program,Grant No.2007CB714705)
文摘Because of the wicked service environment of the high speed train,it is possible that the hollow axle of the train may encounter the foreign object damage and form a sharp notch.Under the fatigue loading a crack can initiate from the notch and propagate to failure.It is noted that the stress intensity factor is the control parameter of the crack propagating,for the purpose of getting the more exact propagation characteristics,the stress intensity factor is studied mainly.The service loads of hollow axles are defined,and the stress distribution of hollow axles is obtained according to the load spectrum.The semi-ellipse crack configuration is defined with three parameters:the aspect ratio,the relative depth and the relative location along the crack front.Quarter point 20-node isoparametric degenerate singular elements are used for the region near the crack tip.The finite element model of crack extension of hollow axle is created,and the crack front is dispersed which can realize orthogonal extension.Based on this the stress intensity factors of crack front were calculated,and the distribution rules of the stress intensity factors of different initial crack shapes are obtained.The conclusions are compared with that of the analytic method and they agree with each other very well,and the calculating results show that there is a close relationship between the stress intensity factor and the initial crack shape.For a round crack the stress intensity factor at the surface point increases faster than the one at the center point with the crock propagation.However,for a narrow crack,the results are in contrast with that of a round one.So,all the cracks with different shapes propagate toward to a similar shape,and they grow at this shape to end.The study may contribute to the crack propagate characteristics research.
基金the Local Capacity Building Project of Shanghai Municipal Science and Technology Commission(No.17090503500)the Young Teachers Training Funding Scheme of Shanghai Colleges and Universities(No.ZZZZyyx16023)。
文摘The wheel diameter difference would worsen the dynamic performance and affect the safety of the rail vehicle.Therefore,it is necessary to detect wheel diameter difference while the train is operating.However,several existing detection methods can’t accurately detect and diagnose the wheel diameter difference under highspeed running environment.In this study,a new method of detecting wheel diameter difference was proposed for high speed rail vehicle.The wheel diameter difference would be diagnosed by the amplitude and frequency of vibration impact on the axle box.Firstly,the dynamic model with varying wheel diameters was established in SIMPACK,and LMA tread was used in high-speed rail vehicles.Then,the simulation results of rail vehicle dynamic performance were compared under different wheel diameter differences.After that,the relationship between axle box vibration and wheel diameter difference was used to demonstrate the feasibility of this detection technology.Finally,comparing and analyzing the simulation results of vibration obtained by matching treads with different wheel diameters,it shows that by increasing the wheel diameter difference,the longitudinal and lateral impacts on axle boxes increase asymmetrically,and the amplitude and the frequency become more evident.Therefore,this paper presents a technical scheme of online measuring wheel diameter difference by monitoring the vibration of the axle box.
基金supported by National Key R&D Program of China(No.2017YFB0304600).
文摘The microstructure,precipitates and properties of 25CrNiMoV(DZ2)steel for high-speed railway axles with different Nb contents were investigated by means of optical microscopy,scanning electron microscopy,electron back-scattering diffraction,transmission electron microscopy and physicochemical phase analysis.The results show that the grain size of the original austenite of the test steels decreases from 20.5 to 14.2 and 10.8μm after adding 0.026 and 0.039 wt.%Nb to a 25CrNiMoV steel,respectively.Moreover,the block width of the tempered martensite in the test steels is refined from 1.91 to 1.72 and 1.60µm,respectively.MC-type precipitates in 25CrNiMoV steel are mainly VC,while(Nb,V)C gradually precipitates when Nb is microalloyed,and the amount of precipitates increases with increasing Nb content.Through strengthening mechanism analysis,it is found that grain refinement strengthening is the primary way to increase the strength.The improvement in the yield strength with increasing Nb content is attributed to a significant increase in precipitation strengthening,grain refinement strengthening and dislocation strengthening.
