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
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
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
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 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
Equivalent axle load factor(EALF)is used to characterize the fatigue damage effect of multi-axle loads on asphalt pavement.EALF is calculated as the ratio of the pavement’s fatigue resistance under a single axle load...Equivalent axle load factor(EALF)is used to characterize the fatigue damage effect of multi-axle loads on asphalt pavement.EALF is calculated as the ratio of the pavement’s fatigue resistance under a single axle load to that under a multi-axle load.Existing studies use the same fatigue life function to predict the fatigue life of asphalt mixture under both single-and multi-axle loads,primarily focusing on the differences in pavement strains under these two configurations.However,strain waveforms in asphalt pavement caused by multi-axle loads differ from those under single-axle loads,altering the mixture’s fatigue behavior.To address this issue,this research tests the fatigue responses of asphalt mixtures under actual loading waveforms from single-axle,tandem-axle,and tridem-axle loads.Based on the test results,fatigue life functions are developed for each axle configuration and used to establish an updated EALF model.Since the applied fatigue life functions are based on test results from more realistic strain waveforms,the calculated EALFs provide more reliable predictions of the damaging effect of multi-axle loads on asphalt mixtures.展开更多
As China's high-speed railway technology advances,high-speed trains have emerged as a pivotal mode of transportation,instrumental in facilitating passenger and freight mobility while fostering robust regional eco-...As China's high-speed railway technology advances,high-speed trains have emerged as a pivotal mode of transportation,instrumental in facilitating passenger and freight mobility while fostering robust regional eco-nomic and trade interactions.Nonetheless,the safety of train operations remains a paramount concern,prompting extensive research into the dynamic behavior of critical components,which is essential to ensuring seamless and secure transportation services.This article commences by comprehensively reviewing the current landscape and evolutionary trajectory of dynamic model analysis for both traditional bearings and axle box bearings.Emphasis is placed on elucidating the profound influence of diverse bearing fault types on the system's kinematic state,alongside delving into the research methodologies employed in developing multi-physics field coupling models.Subsequently,it expounds on the content of investigations focusing on various wheel and track impairments,grounded in the dynamic modeling of the bearing vehicle coupling system.Concurrently,the intricate interplay between wheel-rail excitation and axle box bearing faults on the system's performance is elucidated.Concludingly,the article underscores the inadequacy of current multi-source fault diagnosis meth-odologies in tackling the intricacies of complex train operating environments,thereby highlighting its sig-nificance as a pressing and vital research agenda for the future.展开更多
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
The axle box bearings of high-speed trains often operate in extremely harsh environments,bearing loads from different directions.Long-term operation and frequent changes in working conditions can easily lead to axle b...The axle box bearings of high-speed trains often operate in extremely harsh environments,bearing loads from different directions.Long-term operation and frequent changes in working conditions can easily lead to axle box bearing failures.Therefore,it is extremely important to study the mechanism of axle box bearings.Firstly,the medium of thermal deformation establishes a coupling relationship between the system dynamics model and the thermal grid model,and then obtains the thermal force coupling model of the high-speed train axle box bearing.The coupling model is validated from the perspectives of system dynamics response and temperature response,proving its effectiveness in system dynamics response and temperature characteristic response.Comparing the coupling model with the dynamics model,it is found that thermal deformation complicates the dynamic re-sponse.Finally,using the Lundberg-Palmgren(L-P)bearing fatigue calculation method and damage accumu-lation theory,the bearing fatigue life is calculated,and it is found that thermal deformation deteriorates the bearing operating environment,reducing the bearing fatigue life.Finally,by comparing the bearing fatigue life under different working conditions,it is concluded that the faster the vehicle speed,the greater the load,and the smaller the initial radial clearance of the bearing,the fatigue life of the bearing is reduced.The shorter the lifespan.展开更多
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 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 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.
基金supported by grants from the National Key R&D Program of China(No.2023YFA1008904)the Guangxi Key Research and Development Project(No.AB22080091)the National Natural Science Foundation of China(No.52108412).
文摘Equivalent axle load factor(EALF)is used to characterize the fatigue damage effect of multi-axle loads on asphalt pavement.EALF is calculated as the ratio of the pavement’s fatigue resistance under a single axle load to that under a multi-axle load.Existing studies use the same fatigue life function to predict the fatigue life of asphalt mixture under both single-and multi-axle loads,primarily focusing on the differences in pavement strains under these two configurations.However,strain waveforms in asphalt pavement caused by multi-axle loads differ from those under single-axle loads,altering the mixture’s fatigue behavior.To address this issue,this research tests the fatigue responses of asphalt mixtures under actual loading waveforms from single-axle,tandem-axle,and tridem-axle loads.Based on the test results,fatigue life functions are developed for each axle configuration and used to establish an updated EALF model.Since the applied fatigue life functions are based on test results from more realistic strain waveforms,the calculated EALFs provide more reliable predictions of the damaging effect of multi-axle loads on asphalt mixtures.
基金Supported by the National Natural Science Foundation of China(Grant Nos.12393783,12302067,12172235,52072249)Joint Funds of the National Natural Science Foundation of China(Grant No.U24A2003)+3 种基金College Education Scientific Research Project of Hebei Province(Grant No.JZX2024006)Central Guiding Local Scientific and Technological Development Funding Project(Grant No.246Z2206G)the Key Research Project of China State Railway Group Co.,Ltd.(Grant No.N2024T009)S&T Program of Hebei(Grant No.21567622H).
文摘As China's high-speed railway technology advances,high-speed trains have emerged as a pivotal mode of transportation,instrumental in facilitating passenger and freight mobility while fostering robust regional eco-nomic and trade interactions.Nonetheless,the safety of train operations remains a paramount concern,prompting extensive research into the dynamic behavior of critical components,which is essential to ensuring seamless and secure transportation services.This article commences by comprehensively reviewing the current landscape and evolutionary trajectory of dynamic model analysis for both traditional bearings and axle box bearings.Emphasis is placed on elucidating the profound influence of diverse bearing fault types on the system's kinematic state,alongside delving into the research methodologies employed in developing multi-physics field coupling models.Subsequently,it expounds on the content of investigations focusing on various wheel and track impairments,grounded in the dynamic modeling of the bearing vehicle coupling system.Concurrently,the intricate interplay between wheel-rail excitation and axle box bearing faults on the system's performance is elucidated.Concludingly,the article underscores the inadequacy of current multi-source fault diagnosis meth-odologies in tackling the intricacies of complex train operating environments,thereby highlighting its sig-nificance as a pressing and vital research agenda for the future.
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Supported by the National Natural Science Foundation of China(Grant Nos.12393780,12032017,12302067)College Education Scientific Research Project of Hebei Province(Grant No.JZX2024006)Hebei Provincial S&T Program(Grant No.21567622 H).
文摘The axle box bearings of high-speed trains often operate in extremely harsh environments,bearing loads from different directions.Long-term operation and frequent changes in working conditions can easily lead to axle box bearing failures.Therefore,it is extremely important to study the mechanism of axle box bearings.Firstly,the medium of thermal deformation establishes a coupling relationship between the system dynamics model and the thermal grid model,and then obtains the thermal force coupling model of the high-speed train axle box bearing.The coupling model is validated from the perspectives of system dynamics response and temperature response,proving its effectiveness in system dynamics response and temperature characteristic response.Comparing the coupling model with the dynamics model,it is found that thermal deformation complicates the dynamic re-sponse.Finally,using the Lundberg-Palmgren(L-P)bearing fatigue calculation method and damage accumu-lation theory,the bearing fatigue life is calculated,and it is found that thermal deformation deteriorates the bearing operating environment,reducing the bearing fatigue life.Finally,by comparing the bearing fatigue life under different working conditions,it is concluded that the faster the vehicle speed,the greater the load,and the smaller the initial radial clearance of the bearing,the fatigue life of the bearing is reduced.The shorter the lifespan.
