The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendati...The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendation for the allowable strength and lifetime, which hinders the lightweight design of modern railway vehicles. In this study, to ensure the reliability and durability of a brake unit bracket, an attempt was made to integrate the nominal stress method and an advanced damage tolerance method. First, a complex bogie frame was modelled using solid elements instead of plate and beam elements. A hot spot stress region on the bracket was found under an eight-stage load spectrum obtained from the Wuhan–Guangzhou high-speed railway line. Based on the probability of foreign damage, a semi-elliptical surface crack was then assumed for residual life assessment. The results obtained by the cumulative damage and damage tolerance methods show that the brake unit bracket can operate for over 30 years. Moreover, even if a 2-mm depth crack exists, the brake unit bracket can be safely operated for more than 2.27 years, with the hope that the crack can be detected in subsequent maintenance procedures. Finally, an appropriate safety margin was suggested which provides a basis for the life prediction and durability assessment of brake unit brackets of high-speed railways.展开更多
A multiscale methodology using scanning and transmission electron microscope,synchrotron X-ray nano-tomography and micro-tomography,small angle neutron scattering,and in situ synchrotron X-ray diffrac-tion has been us...A multiscale methodology using scanning and transmission electron microscope,synchrotron X-ray nano-tomography and micro-tomography,small angle neutron scattering,and in situ synchrotron X-ray diffrac-tion has been used,to reveal the effect of Fe-rich phases and precipitates on the mechanical behaviour of an Al-Cu-Mn-Fe-Sc-Zr alloy.Theα-Al grains size is reduced from 185.1μm(0 MPa)and 114.3μm(75 MPa)by applied pressure.Moreover,it has been demonstrated that suitable heat treatments modify the 3D morphology of Fe-rich phases from interconnected to a disaggregated structure that improves the mechanical properties of the alloy.The size and morphology evolution of fine precipitates under differ-ent ageing temperature and time are revealed.At ageing temperature of 160℃,the precipitates change from GP zones toθ’(around 75 nm in length)with ageing time increasing from 1 h to 24 h;the Vick-ers hardness increases from 72.0 HV to 110.7HV.The high ductility of the Sc,Zr modified Al-Cu alloy is related to the complex shape and the loss of interconnectivity of the Fe-rich particles due to the heat treatment.The evolution of the crystal lattice strains inα-Al,andβ-Fe calculated during tensile test us-ing in-situ synchrotron X-ray diffraction corroborates the influence of the microstructure in the ductility of the modified alloy.展开更多
The internal oxide precipitates were supposed to be spherical in Wagner’s original theory,while the fol-lowing research demonstrated that this assumption is an exception rather than the truth,which caused deviations ...The internal oxide precipitates were supposed to be spherical in Wagner’s original theory,while the fol-lowing research demonstrated that this assumption is an exception rather than the truth,which caused deviations in the application of this theory.In this study,the internal oxide precipitates have a needle-like and a near-spherical morphology in a Fe-9Cr ferritic and a Fe-17Cr-9Ni austenitic steels after expo-sure to 600℃ deaerated steam for 600 h,respectively.The nano-to-atomic scale characterization shows that the morphology of the internal oxide precipitates is controlled by the structure of the interfaces be-tween the metal matrix and the internal oxide,while the interface structure is mainly affected by the crystallographic structure of the two phases and their orientation relationship.In addition,the internal oxide precipitation-induced volume expansion and the outward Fe diffusion-induced volume shrink oc-cur simultaneously during the oxidation process.The stress status in the internal oxidation zone(IOZ)is the competing result of the two factors,which could dynamically affect the high-temperature oxidation.The results obtained in this study suggest that there is potential to control the distribution,morphology,and interface structure of the internal oxide precipitates by selecting appropriate base metal and internal oxide-forming element,in order to obtain better high-temperature oxidation-resistant materials.展开更多
High‐speed maglev trains are subjected to severe dynamic loads,thus posing a failure hazard.It is necessary to account for the vehicle dynamics to improve the structural strength and fatigue life assessment approach ...High‐speed maglev trains are subjected to severe dynamic loads,thus posing a failure hazard.It is necessary to account for the vehicle dynamics to improve the structural strength and fatigue life assessment approach under harsh routes and super high‐speed grades.As the most critical load‐carrying part between the vehicle body and levitation frames,the swing bar was taken as an example to demonstrate the significance of vehicle dynamics to integrate classical structural strength and fatigue life with the service conditions.A multiphysics‐coupled dynamic model of an alpha improvement scheme for an electromagnetic suspension maglev train capable of 600 km/h was established to investigate the complex dynamic loads and fatigue spectra.Using this model,the structural strength and fatigue life of the wrought swing bars were investigated.Results show only a slight effect on the structural strength and fatigue life of swing bars by the super high‐speed grades.The nonaxial bending moments caused by the uncompensated relative displacement between the vehicle body and bolsters are identified as the decisive factors.The minimum safety factor of the structural strength for wrought swing bars is 1.33,while the minimum fatigue life is 34 years.Both match the design requirements but are not conservative enough.Therefore,further verification and optimization are recommended to improve the design of swing bars.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.11572267)Sichuan Science and Technology Program(Grant No.2017JY0216)+1 种基金Open Research Project of State Key Laboratory for Strength and Vibration of Mechanical Structures of China(Grant No.SV2016-KF-21)Open Research Project of State Key Laboratory of Traction Power of China(Grant No.2018TPL_T03)
文摘The brake unit bracket of a bogie frame is an important load-carrying component, particularly under emergency start/stop conditions. Conventional infinite/safe life approaches provide an over-conservative recommendation for the allowable strength and lifetime, which hinders the lightweight design of modern railway vehicles. In this study, to ensure the reliability and durability of a brake unit bracket, an attempt was made to integrate the nominal stress method and an advanced damage tolerance method. First, a complex bogie frame was modelled using solid elements instead of plate and beam elements. A hot spot stress region on the bracket was found under an eight-stage load spectrum obtained from the Wuhan–Guangzhou high-speed railway line. Based on the probability of foreign damage, a semi-elliptical surface crack was then assumed for residual life assessment. The results obtained by the cumulative damage and damage tolerance methods show that the brake unit bracket can operate for over 30 years. Moreover, even if a 2-mm depth crack exists, the brake unit bracket can be safely operated for more than 2.27 years, with the hope that the crack can be detected in subsequent maintenance procedures. Finally, an appropriate safety margin was suggested which provides a basis for the life prediction and durability assessment of brake unit brackets of high-speed railways.
基金financially supported by the Natural Science Foundation of China(Nos.52104373 and 51901042)the Ba-sic and Applied Basic Foundation of Guangdong Province,China(Nos.2020B1515120065 and 2021B1515140028)the Guangdong Province Office of Education,China(No.2018KQNCX256).
文摘A multiscale methodology using scanning and transmission electron microscope,synchrotron X-ray nano-tomography and micro-tomography,small angle neutron scattering,and in situ synchrotron X-ray diffrac-tion has been used,to reveal the effect of Fe-rich phases and precipitates on the mechanical behaviour of an Al-Cu-Mn-Fe-Sc-Zr alloy.Theα-Al grains size is reduced from 185.1μm(0 MPa)and 114.3μm(75 MPa)by applied pressure.Moreover,it has been demonstrated that suitable heat treatments modify the 3D morphology of Fe-rich phases from interconnected to a disaggregated structure that improves the mechanical properties of the alloy.The size and morphology evolution of fine precipitates under differ-ent ageing temperature and time are revealed.At ageing temperature of 160℃,the precipitates change from GP zones toθ’(around 75 nm in length)with ageing time increasing from 1 h to 24 h;the Vick-ers hardness increases from 72.0 HV to 110.7HV.The high ductility of the Sc,Zr modified Al-Cu alloy is related to the complex shape and the loss of interconnectivity of the Fe-rich particles due to the heat treatment.The evolution of the crystal lattice strains inα-Al,andβ-Fe calculated during tensile test us-ing in-situ synchrotron X-ray diffraction corroborates the influence of the microstructure in the ductility of the modified alloy.
基金This work was financially supported by National Key Re-search and Development Program of China(No.2018YFE0116200)Shanghai Pujiang Program(No.21PJ1406400)+1 种基金EPSRC(Nos.EP/K040375/1,EP/N010868/1,and EP/R009392/1)Prof.Lefu Zhang is acknowledged for providing the samples used in this study.In-strumental Analysis Center of SJTU is also gratefully acknowledged.The atom probe facilities at the University of Oxford are funded by the EPSRC(No.EP/M022803/1).
文摘The internal oxide precipitates were supposed to be spherical in Wagner’s original theory,while the fol-lowing research demonstrated that this assumption is an exception rather than the truth,which caused deviations in the application of this theory.In this study,the internal oxide precipitates have a needle-like and a near-spherical morphology in a Fe-9Cr ferritic and a Fe-17Cr-9Ni austenitic steels after expo-sure to 600℃ deaerated steam for 600 h,respectively.The nano-to-atomic scale characterization shows that the morphology of the internal oxide precipitates is controlled by the structure of the interfaces be-tween the metal matrix and the internal oxide,while the interface structure is mainly affected by the crystallographic structure of the two phases and their orientation relationship.In addition,the internal oxide precipitation-induced volume expansion and the outward Fe diffusion-induced volume shrink oc-cur simultaneously during the oxidation process.The stress status in the internal oxidation zone(IOZ)is the competing result of the two factors,which could dynamically affect the high-temperature oxidation.The results obtained in this study suggest that there is potential to control the distribution,morphology,and interface structure of the internal oxide precipitates by selecting appropriate base metal and internal oxide-forming element,in order to obtain better high-temperature oxidation-resistant materials.
基金National Key R&D Program of China,Grant/Award Numbers:2016YFB1200602‐15,2016YFB1200602‐17National Natural Science Foundation of China,Grant/Award Numbers:U2032121,12192212Open Research Project of State Key Laboratory of Traction Power,Grant/Award Numbers:2021TPL‐T03,2021TPL‐T04,2021TPL‐T06。
文摘High‐speed maglev trains are subjected to severe dynamic loads,thus posing a failure hazard.It is necessary to account for the vehicle dynamics to improve the structural strength and fatigue life assessment approach under harsh routes and super high‐speed grades.As the most critical load‐carrying part between the vehicle body and levitation frames,the swing bar was taken as an example to demonstrate the significance of vehicle dynamics to integrate classical structural strength and fatigue life with the service conditions.A multiphysics‐coupled dynamic model of an alpha improvement scheme for an electromagnetic suspension maglev train capable of 600 km/h was established to investigate the complex dynamic loads and fatigue spectra.Using this model,the structural strength and fatigue life of the wrought swing bars were investigated.Results show only a slight effect on the structural strength and fatigue life of swing bars by the super high‐speed grades.The nonaxial bending moments caused by the uncompensated relative displacement between the vehicle body and bolsters are identified as the decisive factors.The minimum safety factor of the structural strength for wrought swing bars is 1.33,while the minimum fatigue life is 34 years.Both match the design requirements but are not conservative enough.Therefore,further verification and optimization are recommended to improve the design of swing bars.
