For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is ...For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is a growing need to improve the services by increasing the speed limit for the conventional lines.This paper aims at studying the influence of train speed on the mechanical behaviours of track-bed materials based on field monitoring data.Emphasis is put on the behaviours of interlayer and subgrade soils.The selected experimental site is located in Vierzon,France.Several sensors including accelerometers and soil pressure gauges were installed at different depths.The vertical strains of different layers can be obtained by integrating the records of accelerometers installed at different trackbed depths.The experimentation was carried out using an intercity test train running at different speeds from 60 km/h to 200 km/h.This test train was composed of a locomotive(22.5 Mg/axle) and 7 'Corail'coaches(10.5 Mg/axle).It was observed that when the train speed was raised,the loadings transmitted to the track-bed increased.Moreover,the response of the track-bed materials was amplified by the speed rise at different depths:the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading,and the vertical strains doubled their quasistatic values in the shallow layers.Moreover,the stressestrain paths were estimated using the vertical stress and strain for each train speed.These loading paths allowed the resilient modulus Mrto be determined.It was found that the resilient modulus(M_r) was decreased by about 10% when the train speed was increased from 100 km/h to 200 km/h.However,the damping ratio(D_r) kept stable in the range of speeds explored.展开更多
基于激光粉末床熔融(Laser Powder Bed Fusion,LPBF)成形技术,针对工艺参数对铝合金熔道成形质量的影响规律进行研究。通过工艺实验与数值仿真,阐明LPBF成形过程中输入线能量密度(Linear Energy Density,LED)对熔道成形质量稳定性的影...基于激光粉末床熔融(Laser Powder Bed Fusion,LPBF)成形技术,针对工艺参数对铝合金熔道成形质量的影响规律进行研究。通过工艺实验与数值仿真,阐明LPBF成形过程中输入线能量密度(Linear Energy Density,LED)对熔道成形质量稳定性的影响规律。结果表明随着输入线能量密度的升高,熔道稳定性先升高后降低。当输入线能量密度在0.55~1.0 J/mm时,熔道表面光滑,粉末黏附颗粒少,熔道高度数值离散程度小,成形质量稳定。当线能量密度相同时,适当增加激光功率可以提升熔道成形质量的稳定性。展开更多
基金part of the results obtained within the ‘INVICSA’ research project funded by SNCF-INFRASTRUCTURE and the ANRT with a CIFRE funding number 2012/1150
文摘For the 30,000 km long French conventional railway lines(94% of the whole network),the train speed is currently limited to 220 km/h,whilst the speed is 320 km/h for the 1800 km long high-speed lines.Nowadays,there is a growing need to improve the services by increasing the speed limit for the conventional lines.This paper aims at studying the influence of train speed on the mechanical behaviours of track-bed materials based on field monitoring data.Emphasis is put on the behaviours of interlayer and subgrade soils.The selected experimental site is located in Vierzon,France.Several sensors including accelerometers and soil pressure gauges were installed at different depths.The vertical strains of different layers can be obtained by integrating the records of accelerometers installed at different trackbed depths.The experimentation was carried out using an intercity test train running at different speeds from 60 km/h to 200 km/h.This test train was composed of a locomotive(22.5 Mg/axle) and 7 'Corail'coaches(10.5 Mg/axle).It was observed that when the train speed was raised,the loadings transmitted to the track-bed increased.Moreover,the response of the track-bed materials was amplified by the speed rise at different depths:the vertical dynamic stress was increased by about 10% when the train speed was raised from 60 km/h to 200 km/h for the locomotive loading,and the vertical strains doubled their quasistatic values in the shallow layers.Moreover,the stressestrain paths were estimated using the vertical stress and strain for each train speed.These loading paths allowed the resilient modulus Mrto be determined.It was found that the resilient modulus(M_r) was decreased by about 10% when the train speed was increased from 100 km/h to 200 km/h.However,the damping ratio(D_r) kept stable in the range of speeds explored.
文摘基于激光粉末床熔融(Laser Powder Bed Fusion,LPBF)成形技术,针对工艺参数对铝合金熔道成形质量的影响规律进行研究。通过工艺实验与数值仿真,阐明LPBF成形过程中输入线能量密度(Linear Energy Density,LED)对熔道成形质量稳定性的影响规律。结果表明随着输入线能量密度的升高,熔道稳定性先升高后降低。当输入线能量密度在0.55~1.0 J/mm时,熔道表面光滑,粉末黏附颗粒少,熔道高度数值离散程度小,成形质量稳定。当线能量密度相同时,适当增加激光功率可以提升熔道成形质量的稳定性。
