Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint ...Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.展开更多
As a vehicle passing through a track with different weld irregularities, the dynamic performance of track com- ponents is investigated in detail by using a coupled vehi- cle-track model. In the model, the vehicle is m...As a vehicle passing through a track with different weld irregularities, the dynamic performance of track com- ponents is investigated in detail by using a coupled vehi- cle-track model. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom, and a Timoshenko beam is used to model the rails which are dis- cretely supported by sleepers. In the track model, the sleepers are modeled as rigid bodies accounting for their vertical, lat- eral and rolling motions and assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the study of the coupled vehicle and track dynamics, the Hertizian contact theory and the theory proposed by Shen-Hedrick-Elkins are, respectively, used to calculate normal and creep forces between the wheel and the rails. In the calculation of the normal forces, the coefficient of the normal contact stiffness is determined by transient contact condition of the wheel and rail surface. In the calcu- lation of the creepages, the lateral, roll-over motions of the rail and the fact that the relative velocity between the wheel and rail in their common normal direction is equal to zero are simultaneously taken into account. The motion equations of the vehicle and track are solved by means of an explicit integration method, in which the rail weld irregularities are modeled as local track vertical deviations described by some ideal cosine functions. The effects of the train speed, the axle load, the wavelength and depth of the irregularities, and the weld center position in a sleeper span on the wheel-rail impact loading are analyzed. The numerical results obtained are greatly useful in the tolerance design of welded rail pro- file irregularity caused by hand-grinding after rail welding and track maintenances.展开更多
The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail(CWR)brings great challenges to CWR designing.Taking a suspension bridge with laying CWR as a case,the mechanical propertie...The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail(CWR)brings great challenges to CWR designing.Taking a suspension bridge with laying CWR as a case,the mechanical properties of CWR on the bridge are analyzed to reveal the sensitive areas of the track,and the design method of CWR and track structures on the beam ends are proposed.The results show that the unidirectional Rail Expansion Joints(REJ)need to be installed on the beam end of the kilometer-span bridge to reduce rail longitudinal force.Due to the bridge characteristics,there is no CWR fixed area on the kilometer-span bridge,and rail longitudinal force on the main span caused by bending loads needs to be concerned.The deformation of track on the beam end is complex,which is the weak area on the kilometer bridge,the large relative displacement between the stock rail of REJ and the main beam can cause poor stability of ballast bed on beam end,small resistance fasteners need to be laid on the sides of stock rail on the main beam to increase the stability of ballast and fasteners on the beam end.To improve the driving safety and comfort of beam end,the Sleeper-Supporting Apparatus(SSA)should be specially designed to ensure the uniform transition of track on beam ends.Temperature and wind loads have a significant impact on track regularity on the kilometer span bridge,the dynamic response of trains and bridges under those loads needs to be attended to.展开更多
Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete ...Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube(CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a(77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail(CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load.Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.展开更多
Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of...Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fi'acture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation aider frac- ture and percentage reduction of area) and the toughness indices (Charpy impact energy Ak and plane-strain fracture toughness Kic) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and Klc values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.展开更多
A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement ...A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement (among) the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.展开更多
The effect of preheating temperature on the mechanical and fracture behavior, hardness, and the microstructure of slot welded pearlitic rail steel were studied. Railhead sections with slots were preheated to 200℃, 30...The effect of preheating temperature on the mechanical and fracture behavior, hardness, and the microstructure of slot welded pearlitic rail steel were studied. Railhead sections with slots were preheated to 200℃, 300℃, 350℃ and 400℃?before gas metal arc filling to simulate defects repair. Another sample, welded at room temperature (RT) with no preheat, was studied in comparison. The parent rail steel has ultimate strength, yield strength and strain to failure of 1146 MPa, 717 MPa and 9.3%, respectively. Optimum values of these properties for the welded rail steels were found to be 1023 MPa, 655 MPa and 4.7%, respectively, for the 200℃ preheat temperature. On this basis, the optimum weld efficiency was found to be 89.2%. The average apparent fracture toughness KI for the parent rail was 127 MPa.m0.5, while that for the optimum welded joint (200℃ preheat) was 116.5 MPa.m0.5. In addition, the average hardness values of the weld, fusion zone, and heat affected zone (HAZ) were 313.5, 332 and 313.6 HB, respectively, while that for parent rail steel was about 360 HB. Dominance of bainite and acicular ferrite phase in the weld microstructure was observed at 200℃ preheat.展开更多
An innovation is conducted on a K190πK rail auto welding machine because of its poor stability in quality of welding joints. A new control system based on a programmable controller is designed to replace the old o...An innovation is conducted on a K190πK rail auto welding machine because of its poor stability in quality of welding joints. A new control system based on a programmable controller is designed to replace the old one. The new control system is of higher accuracy in controlling sequence and good ability in anti disturbance, and is convenient to operate. The comparison tests are carried out. The experimental results show that the quality of welded joints is greatly increased by the improved welding mechine.展开更多
This paper describes the economic and technological benefits of installing continuous welded rail (CWR) track on sharp (radius≤300 m) railway curves. A new form of prestressed concrete sleepers developed by the V...This paper describes the economic and technological benefits of installing continuous welded rail (CWR) track on sharp (radius≤300 m) railway curves. A new form of prestressed concrete sleepers developed by the V. Lazaryan Dniprope- trovsk National University of Railway Transport is shown to improve the lateral shift resistance of CWR track in sharp curves and the use of anchor sleepers on tangents is shown to make it possible to lower the fastening temperature of the CWR track in order to increase the rail lifespan.展开更多
A kind of heat treatment technology of thermit welds was introduced in this paper. Through the heal treatment not only the mechanical properties are improved, but the hardness of head was redistributed. Heat treatreat...A kind of heat treatment technology of thermit welds was introduced in this paper. Through the heal treatment not only the mechanical properties are improved, but the hardness of head was redistributed. Heat treatreatment alleviated the soften of the quenched rail clue to welding. The technology has been successfully applied to lay the lines and crosses at Da-qin continuous line.展开更多
文摘Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.
基金supported by the National Basic Research Program of China(2007CB714702)the National Natural Science Foundation of China(50821063,50675183 and 50875221)
文摘As a vehicle passing through a track with different weld irregularities, the dynamic performance of track com- ponents is investigated in detail by using a coupled vehi- cle-track model. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom, and a Timoshenko beam is used to model the rails which are dis- cretely supported by sleepers. In the track model, the sleepers are modeled as rigid bodies accounting for their vertical, lat- eral and rolling motions and assumed to move backward at a constant speed to simulate the vehicle running along the track at the same speed. In the study of the coupled vehicle and track dynamics, the Hertizian contact theory and the theory proposed by Shen-Hedrick-Elkins are, respectively, used to calculate normal and creep forces between the wheel and the rails. In the calculation of the normal forces, the coefficient of the normal contact stiffness is determined by transient contact condition of the wheel and rail surface. In the calcu- lation of the creepages, the lateral, roll-over motions of the rail and the fact that the relative velocity between the wheel and rail in their common normal direction is equal to zero are simultaneously taken into account. The motion equations of the vehicle and track are solved by means of an explicit integration method, in which the rail weld irregularities are modeled as local track vertical deviations described by some ideal cosine functions. The effects of the train speed, the axle load, the wavelength and depth of the irregularities, and the weld center position in a sleeper span on the wheel-rail impact loading are analyzed. The numerical results obtained are greatly useful in the tolerance design of welded rail pro- file irregularity caused by hand-grinding after rail welding and track maintenances.
基金supported by the National Key R&D Program of China(2022YFB2602901)the National Natural Science Foundation of China(No.52178405).
文摘The complex bridge-track interaction between kilometer-span bridges and continuous Welded Rail(CWR)brings great challenges to CWR designing.Taking a suspension bridge with laying CWR as a case,the mechanical properties of CWR on the bridge are analyzed to reveal the sensitive areas of the track,and the design method of CWR and track structures on the beam ends are proposed.The results show that the unidirectional Rail Expansion Joints(REJ)need to be installed on the beam end of the kilometer-span bridge to reduce rail longitudinal force.Due to the bridge characteristics,there is no CWR fixed area on the kilometer-span bridge,and rail longitudinal force on the main span caused by bending loads needs to be concerned.The deformation of track on the beam end is complex,which is the weak area on the kilometer bridge,the large relative displacement between the stock rail of REJ and the main beam can cause poor stability of ballast bed on beam end,small resistance fasteners need to be laid on the sides of stock rail on the main beam to increase the stability of ballast and fasteners on the beam end.To improve the driving safety and comfort of beam end,the Sleeper-Supporting Apparatus(SSA)should be specially designed to ensure the uniform transition of track on beam ends.Temperature and wind loads have a significant impact on track regularity on the kilometer span bridge,the dynamic response of trains and bridges under those loads needs to be attended to.
基金Project(51378503)supported by the National Natural Science Foundation of ChinaProject(2014M552158)supported by China Postdoctoral Science Foundation
文摘Considering arch rib, lateral brace, suspender, girder, pier and track position, the model for the interaction between long-span tied arch continuous bridge and multiple tracks was established by using steel-concrete composite section beam element to simulate concrete-filled steel tube(CFST) arch rib, using the beam element with rigid arm to simulate the prestressed concrete girder and using nonlinear bar element to simulate longitudinal constraint between track and bridge. Taking a(77+3×156.8+77) m tied arch continuous bridge with four tracks on the Harbin-Qiqihar Passenger Dedicated Line as an example, the arrangement of continuously welded rail(CWR) was explored. The longitudinal force in CWR on the tied arch continuous bridge, the pier top horizontal force and torque due to the unbalance load case, were analyzed under the action of temperature, vertical live load, train braking and wind load.Studies show that, it can significantly reduce track displacement to set the track expansion devices at main span arch springing on both sides; the track stress due to arch temperature variation can reach 40.8 MPa; the track stress, pier top horizontal force and torque are related to the number of loaded tracks and train running direction, and the bending force applied to unloaded track is close to the loaded track, while the braking force applied to unloaded track is 1/4 to 1/2 of the loaded track; the longitudinal force of track due to the wind load is up to 12.4 MPa, which should be considered.
基金supported by the Research Foundation of the Ministry of Railways and Tsinghua University (No.T200410)the National Natural Science Foundation of China (Nos.50778102 and 51178244)
文摘Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fi'acture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation aider frac- ture and percentage reduction of area) and the toughness indices (Charpy impact energy Ak and plane-strain fracture toughness Kic) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and Klc values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.
文摘A new mechanics model, which reveals additional longitudinal force transmission between the continuously welded rails and the bridges, is established on the fact that the influence of the mutual relative displacement (among) the rail, the sleeper and the beam is taken into account. An example is presented and numerical results are compared. The results show that the additional longitudinal forces calculated with the new model are less than those of the previous, especially in the case of the flexible pier bridges. The new model is also suitable for the analysis of the additional longitudinal force transmission between rails and bridges of ballastless track with small resistance fasteners without taking the sleeper displacement into account, and compared with the ballast bridges, the ballastless bridges have a much stronger additional longitudinal force transmission between the continuously welded rails and the bridges.
文摘The effect of preheating temperature on the mechanical and fracture behavior, hardness, and the microstructure of slot welded pearlitic rail steel were studied. Railhead sections with slots were preheated to 200℃, 300℃, 350℃ and 400℃?before gas metal arc filling to simulate defects repair. Another sample, welded at room temperature (RT) with no preheat, was studied in comparison. The parent rail steel has ultimate strength, yield strength and strain to failure of 1146 MPa, 717 MPa and 9.3%, respectively. Optimum values of these properties for the welded rail steels were found to be 1023 MPa, 655 MPa and 4.7%, respectively, for the 200℃ preheat temperature. On this basis, the optimum weld efficiency was found to be 89.2%. The average apparent fracture toughness KI for the parent rail was 127 MPa.m0.5, while that for the optimum welded joint (200℃ preheat) was 116.5 MPa.m0.5. In addition, the average hardness values of the weld, fusion zone, and heat affected zone (HAZ) were 313.5, 332 and 313.6 HB, respectively, while that for parent rail steel was about 360 HB. Dominance of bainite and acicular ferrite phase in the weld microstructure was observed at 200℃ preheat.
文摘An innovation is conducted on a K190πK rail auto welding machine because of its poor stability in quality of welding joints. A new control system based on a programmable controller is designed to replace the old one. The new control system is of higher accuracy in controlling sequence and good ability in anti disturbance, and is convenient to operate. The comparison tests are carried out. The experimental results show that the quality of welded joints is greatly increased by the improved welding mechine.
文摘This paper describes the economic and technological benefits of installing continuous welded rail (CWR) track on sharp (radius≤300 m) railway curves. A new form of prestressed concrete sleepers developed by the V. Lazaryan Dniprope- trovsk National University of Railway Transport is shown to improve the lateral shift resistance of CWR track in sharp curves and the use of anchor sleepers on tangents is shown to make it possible to lower the fastening temperature of the CWR track in order to increase the rail lifespan.
文摘A kind of heat treatment technology of thermit welds was introduced in this paper. Through the heal treatment not only the mechanical properties are improved, but the hardness of head was redistributed. Heat treatreatment alleviated the soften of the quenched rail clue to welding. The technology has been successfully applied to lay the lines and crosses at Da-qin continuous line.