To study the microstructural evolution of pearlite steel subjected to pure rolling and rolling-sliding contact loading,a hypoeutectoid pearlite steel with composition and microstructure similar to BS11 was designed an...To study the microstructural evolution of pearlite steel subjected to pure rolling and rolling-sliding contact loading,a hypoeutectoid pearlite steel with composition and microstructure similar to BS11 was designed and twindisc tests of this pearlite steel were performed to simulate the wheel/rail system.After a series of twin-disc tests,optical microscope（OM）observation,scanning electron microscope（SEM）observation,X-ray diffraction（XRD）,and micro-hardness tests were conducted to characterize the microstructure.Under the pure rolling contact condition,a large amount of reticular cracks emerged within 60μm below the contact surface of the samples after 120 000 revolutions.The largest deformation was approximately 200μm below the contact surface.Under the rolling-sliding contact condition,the nodularization of pearlite within 100μm below the contact surface was obvious.The microstructure and stress-strain distribution of the area within 2mm below the contact surface were investigated.The distribution of micro-hardness under the contact surface varied with contact conditions.Finite element method（FEM）was used to simulate the stress-strain distribution.The results of SEM,FEM,and micro-hardness tests indicated that under the pure rolling contact condition,the maximum plastic strain was approximately 200-400μm below the contact surface.Conversely,under the rolling-sliding contact condition,the maximum plastic strain emerged on the contact surface.Under the pure rolling contact condition,the distribution of micro-hardness was almost identical to that of the equivalent plastic strain.Under the rolling-sliding contact condition,the distribution of micro-hardness was affected by the equivalent plastic strain and tangential stress.展开更多
Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature fiel...Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-meehanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.展开更多
Experime ntal research results of surface damage accumulation in rail steel under rolling with slippage are presented. Hertz contact for two rollers made of rail and whe el steels was realized in the test. The influe...Experime ntal research results of surface damage accumulation in rail steel under rolling with slippage are presented. Hertz contact for two rollers made of rail and whe el steels was realized in the test. The influence of loading regime upon wear of rail is considered. The estimation of characteristics of surface fracture resis tance for rail steel is made. The method to predict the life of rail steel under given conditions of regular loading is proposed.展开更多
The analytical elastoplastic rolling/sliding model for two-dimensional contact proposed by McDowell is an important tool for predicting residual stress in rolling/sliding processes. In application of the model, a prob...The analytical elastoplastic rolling/sliding model for two-dimensional contact proposed by McDowell is an important tool for predicting residual stress in rolling/sliding processes. In application of the model, a problem of low predicting precision near the surface layer of the component is found. According to the volume- constancy of plastic deformation, an improved algorithm for McDowell＇s model is proposed in order to improve its predicting accuracy of the surface residual stress. In the algorithm, a relationship between three normal stresses perpendicular to each other at any point within the component is derived, and the relationship is applied to McDowell＇s model. Meanwhile, an unnecessary hypothesis proposed by McDowell can be eliminated to make the model more reasonable. The simulation results show that the surface residual stress predicted by modified method is much closer to the FEM results than the results predicted by McDowell＇s model under the same simulation conditions.展开更多
Microstructure evolution or degradation has been well recognized to be closely related to the formation of microcracks in pearlitic rails and wheels.The rolling contact fatigue machine was employed to simulate the rai...Microstructure evolution or degradation has been well recognized to be closely related to the formation of microcracks in pearlitic rails and wheels.The rolling contact fatigue machine was employed to simulate the rail-wheel contact,and the microstructure evolution and crack formation of pearlitic steels subjected to rolling-sliding contact loading were then experimentally characterized.To further quantitatively predict the fracture behaviors,a phase-field model was herein established to investigate the cyclic loading-driven microstructure evolution and the microstructure-dependent fracture resistance in pearlite.The coupling of microstructure evolution and crack propagation was realized through the introduction of two-set order parameters,i.e.,the crack field and the microstructure field,and the microstructure-dependent fracture toughness.The proposed model can predict the fracture resistance of microstructure at different depths from the contact surface,after different rolling cycles and with different initial pearlitic microstructures,which can shed light on the design of damage-resistant microstructure of pearlitic steels.展开更多
The rolling contact fatigue(RCF)model is commonly used to predict the contact fatigue life when the sliding is insignificant in contact surfaces.However,many studies reveal that the sliding,compared to the rolling sta...The rolling contact fatigue(RCF)model is commonly used to predict the contact fatigue life when the sliding is insignificant in contact surfaces.However,many studies reveal that the sliding,compared to the rolling state,can lead to a considerable reduction of the fatigue life and an excessive increase of the pitting area,which result from the microscopic stress cycle growth caused by the sliding of the asperity contact.This suggests that fatigue life in the rolling-sliding condition can be overestimated based only on the RCF model.The rubbing surfaces of spiral bevel gears are subject to typical rolling-sliding motion.This paper aims to study the mechanism of the micro stress cycle along the meshing path and provide a reasonable method for predicting the fatigue life in spiral bevel gears.The microscopic stress cycle equation is derived with the consideration of gear meshing parameters.The combination of the RCF model and asperity stress cycle is developed to calculate the fatigue life in spiral bevel gears.We find that the contact fatigue life decreases significantly compared with that obtained from the RCF model.There is strong evidence that the microscopic stress cycle is remarkably increased by the rolling-sliding motion of the asperity contact,which is consistent with the experimental data in previous literature.In addition,the fatigue life under different assembling misalignments are investigated and the results demonstrate the important role of misalignments on fatigue life.展开更多
基金Item Sponsored by National Basic Research Programs of China(2015GB118001,2015CB654802)
文摘To study the microstructural evolution of pearlite steel subjected to pure rolling and rolling-sliding contact loading,a hypoeutectoid pearlite steel with composition and microstructure similar to BS11 was designed and twindisc tests of this pearlite steel were performed to simulate the wheel/rail system.After a series of twin-disc tests,optical microscope（OM）observation,scanning electron microscope（SEM）observation,X-ray diffraction（XRD）,and micro-hardness tests were conducted to characterize the microstructure.Under the pure rolling contact condition,a large amount of reticular cracks emerged within 60μm below the contact surface of the samples after 120 000 revolutions.The largest deformation was approximately 200μm below the contact surface.Under the rolling-sliding contact condition,the nodularization of pearlite within 100μm below the contact surface was obvious.The microstructure and stress-strain distribution of the area within 2mm below the contact surface were investigated.The distribution of micro-hardness under the contact surface varied with contact conditions.Finite element method（FEM）was used to simulate the stress-strain distribution.The results of SEM,FEM,and micro-hardness tests indicated that under the pure rolling contact condition,the maximum plastic strain was approximately 200-400μm below the contact surface.Conversely,under the rolling-sliding contact condition,the maximum plastic strain emerged on the contact surface.Under the pure rolling contact condition,the distribution of micro-hardness was almost identical to that of the equivalent plastic strain.Under the rolling-sliding contact condition,the distribution of micro-hardness was affected by the equivalent plastic strain and tangential stress.
基金supported by National Natural Science Foundation of China(Grant Nos.51175438,U1134202)National Science and Technology Support Program of China(Grant No.2009BAG12A01)Program for New Century Excellent Talents in University of China(Grant No.NCET-08-0824)
文摘Thermal damage caused by frictional heat of rolling-sliding contact is one of the most important failure forms of wheel and rail. Many studies of wheel-rail frictional heating have been devoted to the temperature field, but few literatures focus on wheel-rail thermal stress caused by frictional heating. However, the wheel-rail creepage is one of important influencing factors of the thermal stress In this paper, a thermo-mechanical coupling model of wheel-rail rolling-sliding contact is developed using thermo-elasto-plastic finite element method. The effect of the wheel-rail elastic creepage on the distribution of heat flux is investigated using the numerical model in which the temperature-dependent material properties are taken into consideration. The moving wheel-rail contact force and the frictional heating are used to simulate the wheel rolling on the rail. The effect of the creepage on the temperature rise, thermal strain, residual stress and residual strain under wheel-rail sliding-rolling contact are investigated. The investigation results show that the thermally affected zone exists mainly in a very thin layer of material near the rail contact surface during the rolling-sliding contact. Both the temperature and thermal strain of rail increase with increasing creepage. The residual stresses induced by the frictional heat in the surface layer of rail appear to be tensile. When the creepage is large, the frictional heat has a significant influence on the residual stresses and residual strains of rail. This paper develops a thermo-meehanical coupling model of wheel-rail rolling-sliding contact, and the obtained results can help to understand the mechanism of wheel/rail frictional thermal fatigue.
基金SupportedbytheNationalNaturalScienceFoundationofChina (No .5 9935 10 0 )
文摘Experime ntal research results of surface damage accumulation in rail steel under rolling with slippage are presented. Hertz contact for two rollers made of rail and whe el steels was realized in the test. The influence of loading regime upon wear of rail is considered. The estimation of characteristics of surface fracture resis tance for rail steel is made. The method to predict the life of rail steel under given conditions of regular loading is proposed.
文摘The analytical elastoplastic rolling/sliding model for two-dimensional contact proposed by McDowell is an important tool for predicting residual stress in rolling/sliding processes. In application of the model, a problem of low predicting precision near the surface layer of the component is found. According to the volume- constancy of plastic deformation, an improved algorithm for McDowell＇s model is proposed in order to improve its predicting accuracy of the surface residual stress. In the algorithm, a relationship between three normal stresses perpendicular to each other at any point within the component is derived, and the relationship is applied to McDowell＇s model. Meanwhile, an unnecessary hypothesis proposed by McDowell can be eliminated to make the model more reasonable. The simulation results show that the surface residual stress predicted by modified method is much closer to the FEM results than the results predicted by McDowell＇s model under the same simulation conditions.
基金Chi Zhang acknowledges the financial support from the National Natural Science Foundation of China(Grant No.51771097)the National Program on Key Basic Research Project(973 Program,Grant No.2015CB654802)+2 种基金the National Magnetic Confinement Fusion Energy Research Project of China(Grant No.2015GB118001)the Science Challenge Project(Grant No.TZ2018004)Lei Chen is grateful for the financial support by NSF under CBET-1604104.
文摘Microstructure evolution or degradation has been well recognized to be closely related to the formation of microcracks in pearlitic rails and wheels.The rolling contact fatigue machine was employed to simulate the rail-wheel contact,and the microstructure evolution and crack formation of pearlitic steels subjected to rolling-sliding contact loading were then experimentally characterized.To further quantitatively predict the fracture behaviors,a phase-field model was herein established to investigate the cyclic loading-driven microstructure evolution and the microstructure-dependent fracture resistance in pearlite.The coupling of microstructure evolution and crack propagation was realized through the introduction of two-set order parameters,i.e.,the crack field and the microstructure field,and the microstructure-dependent fracture toughness.The proposed model can predict the fracture resistance of microstructure at different depths from the contact surface,after different rolling cycles and with different initial pearlitic microstructures,which can shed light on the design of damage-resistant microstructure of pearlitic steels.
基金National Science Foundation of China(No.51875369)General Projects of Basic Science and Frontier Technology Research of Chongqing(Nos.cstc2016jcyjA0511,cstc2018jcyjAX0451)Wei PU would like to thank Fundamental Research Funds for the Central Universities(No.YjJ201752).
文摘The rolling contact fatigue(RCF)model is commonly used to predict the contact fatigue life when the sliding is insignificant in contact surfaces.However,many studies reveal that the sliding,compared to the rolling state,can lead to a considerable reduction of the fatigue life and an excessive increase of the pitting area,which result from the microscopic stress cycle growth caused by the sliding of the asperity contact.This suggests that fatigue life in the rolling-sliding condition can be overestimated based only on the RCF model.The rubbing surfaces of spiral bevel gears are subject to typical rolling-sliding motion.This paper aims to study the mechanism of the micro stress cycle along the meshing path and provide a reasonable method for predicting the fatigue life in spiral bevel gears.The microscopic stress cycle equation is derived with the consideration of gear meshing parameters.The combination of the RCF model and asperity stress cycle is developed to calculate the fatigue life in spiral bevel gears.We find that the contact fatigue life decreases significantly compared with that obtained from the RCF model.There is strong evidence that the microscopic stress cycle is remarkably increased by the rolling-sliding motion of the asperity contact,which is consistent with the experimental data in previous literature.In addition,the fatigue life under different assembling misalignments are investigated and the results demonstrate the important role of misalignments on fatigue life.
