A series of single track clads of Inconel 625 alloy were fabricated by laser solid forming.To achieve the high dimensional accuracy and excellent mechanical properties,the effect of processing parameters on the geomet...A series of single track clads of Inconel 625 alloy were fabricated by laser solid forming.To achieve the high dimensional accuracy and excellent mechanical properties,the effect of processing parameters on the geometry,the formation of Laves phase and the residual stress was investigated.The results show that laser power and scanning speed had a dramatical influence on the width and height of single-track clads.According to the columnar to equiaxed transition curve of Inconel 625,the grain morphology can be predicted during the LSF process.With the increasing laser power and the decreasing scanning speed,the segregation degree of Si,Nb,Mo,the volume fraction and size of Laves phase increased.Vickers indentation was used to demonstrate that optimizing processing parameter can achieve the minimum residual tensile stress.展开更多
The cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses.However,the mechanism of the irregul...The cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses.However,the mechanism of the irregularities initiation and development is unclear.The motivation of the present study was the previous experimental studies on the application of wide sleepers in the ballasted track.The long-term track geometry measurements with wide sleepers show an enormous reduction of the vertical longitudinal irregularities compared to the conventional track.However,wide sleepers had higher twist and cross-section level irregularities.The present paper aims to explain the phenomenon by discrete element method(DEM)modeling the development process of sleeper inhomogeneous support at cross-level depending on the sleeper form.The DEM simulations show that the maximal settlement intensity is up to 3.5 times lower for a wide sleeper in comparison with the conventional one.Nevertheless,the cross-level differential settlements are almost the same for both sleepers.The particle loading distribution after all loading cycles is concentrated on the smaller area,up to the half sleeper length,with fully unloaded zones under sleeper ends.Ballast flow limitation under the central part of the sleeper could improve the resilience of wide sleepers to the development of cross-level irregularities.The mechanism of initiation of the cross-level irregularity is proposed,which assumes the loss of sleeper support under sleeper ends.The further growth of inhomogeneous settlements along the sleeper is assumed as a result of the interaction of two processes:ballast flow due to dynamic impact during void closing and on the other side high pressure due to the concentration of the pressure under the middle part of the sleeper.The DEM simulation results support the assumption of the mechanism and agree with the experimental studies.展开更多
基金Project(2018YFB1105804)supported by the National Key R&D Program of ChinaProject(2020-TS-06)supported by the Research Fund of the State Key Laboratory of Solidification Processing(NPU),China。
文摘A series of single track clads of Inconel 625 alloy were fabricated by laser solid forming.To achieve the high dimensional accuracy and excellent mechanical properties,the effect of processing parameters on the geometry,the formation of Laves phase and the residual stress was investigated.The results show that laser power and scanning speed had a dramatical influence on the width and height of single-track clads.According to the columnar to equiaxed transition curve of Inconel 625,the grain morphology can be predicted during the LSF process.With the increasing laser power and the decreasing scanning speed,the segregation degree of Si,Nb,Mo,the volume fraction and size of Laves phase increased.Vickers indentation was used to demonstrate that optimizing processing parameter can achieve the minimum residual tensile stress.
文摘The cross-level and twist irregularities are the most dangerous irregularity types that could cause wheel unloading with the risk of derailments and additional maintenance expenses.However,the mechanism of the irregularities initiation and development is unclear.The motivation of the present study was the previous experimental studies on the application of wide sleepers in the ballasted track.The long-term track geometry measurements with wide sleepers show an enormous reduction of the vertical longitudinal irregularities compared to the conventional track.However,wide sleepers had higher twist and cross-section level irregularities.The present paper aims to explain the phenomenon by discrete element method(DEM)modeling the development process of sleeper inhomogeneous support at cross-level depending on the sleeper form.The DEM simulations show that the maximal settlement intensity is up to 3.5 times lower for a wide sleeper in comparison with the conventional one.Nevertheless,the cross-level differential settlements are almost the same for both sleepers.The particle loading distribution after all loading cycles is concentrated on the smaller area,up to the half sleeper length,with fully unloaded zones under sleeper ends.Ballast flow limitation under the central part of the sleeper could improve the resilience of wide sleepers to the development of cross-level irregularities.The mechanism of initiation of the cross-level irregularity is proposed,which assumes the loss of sleeper support under sleeper ends.The further growth of inhomogeneous settlements along the sleeper is assumed as a result of the interaction of two processes:ballast flow due to dynamic impact during void closing and on the other side high pressure due to the concentration of the pressure under the middle part of the sleeper.The DEM simulation results support the assumption of the mechanism and agree with the experimental studies.
