The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elas...The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code.Then,the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software.The effects of welding sequence,clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically.The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure.Compared with the welding sequence,the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure.In the case of30 mm reverse deformation,the maximum deformation can be reduced about 70%in comparison to an actual welding process.展开更多
Copper matrix composites consisting of chromium （Cr） or ferrochrome （Cr-Fe） as strengthening elements and molybdenum disulfide as a lubricant had been sintered in nitrogen and hydrogen atmosphere, respectively. Th...Copper matrix composites consisting of chromium （Cr） or ferrochrome （Cr-Fe） as strengthening elements and molybdenum disulfide as a lubricant had been sintered in nitrogen and hydrogen atmosphere, respectively. Their morphology and energy-dispersive X-ray spectrometry （EDS） analysis showed that serious interaction occurred between MoS2 and Cr （or Cr-Fe） particles when the samples were sintered in hydrogen atmosphere. Chromium sulfide compound （CrxSy） was formed as a reaction product, which decreased the density and strength of the composites remarkably. This interaction was inhibited when the samples were sintered in nitrogen atmosphere; thus, the mechanical properties of the composites were improved.展开更多
A spherical Fe matrix composite powder containing a high volume fraction （82vo1%） of fine TiC reinforcement was produced using a novel process combining in situ synthesis and plasma techniques. The composite powder ...A spherical Fe matrix composite powder containing a high volume fraction （82vo1%） of fine TiC reinforcement was produced using a novel process combining in situ synthesis and plasma techniques. The composite powder exhibited good sphericity and a dense structure, and the fine sub-micron TiC particles were homogeneously distributed in the α-Fe matrix. A TiC-Fe cermet was prepared from the as-prepared spherical composite powder using powder metallurgy at a low sintering temperature; the product exhibited a hardness of HRA 88.5 and a flexural strength of 1360 MPa. The grain size of the fine-grained TiC and special surface structure of the spherical powder played the key roles in the fabrication process.展开更多
The induced airfl w from passing trains,which is recognized as train wind,usually has adverse impacts on people in the surroundings,i.e.,the aerodynamic forces generated by a high-speed train＇s wind may act on the hu...The induced airfl w from passing trains,which is recognized as train wind,usually has adverse impacts on people in the surroundings,i.e.,the aerodynamic forces generated by a high-speed train＇s wind may act on the human body and endanger the safety of pedestrians or roadside workers.In this paper,an improved delayed detached eddy simulation（IDDES） method is used to study train wind.The effects of the affiliate components and train length on train wind are analyzed.The results indicate that the aff liated components and train length have no effect on train wind in the area in front of the leading nose.In the downstream and wake regions,the longitudinal train wind becomes stronger as the length of the train increases,while the transverse train wind is not affected.The presence of affiliate components strengthens the train wind in the near fiel of the train because of strong fl w solid interactions but has limited effects on train wind in the far field.展开更多
基金financial support to this project from the Chinese CSR Qingdao Sifang Co.,Ltd
文摘The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code.Then,the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software.The effects of welding sequence,clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically.The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure.Compared with the welding sequence,the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure.In the case of30 mm reverse deformation,the maximum deformation can be reduced about 70%in comparison to an actual welding process.
基金financially supported by the Key Project of the National Eleventh-Five Year Research Program of China (No.2009BAG12A07)
文摘Copper matrix composites consisting of chromium （Cr） or ferrochrome （Cr-Fe） as strengthening elements and molybdenum disulfide as a lubricant had been sintered in nitrogen and hydrogen atmosphere, respectively. Their morphology and energy-dispersive X-ray spectrometry （EDS） analysis showed that serious interaction occurred between MoS2 and Cr （or Cr-Fe） particles when the samples were sintered in hydrogen atmosphere. Chromium sulfide compound （CrxSy） was formed as a reaction product, which decreased the density and strength of the composites remarkably. This interaction was inhibited when the samples were sintered in nitrogen atmosphere; thus, the mechanical properties of the composites were improved.
基金financially supported by the National Natural Science Foundation of China (No. 51274039)the Research Fund for the Doctoral Program of Higher Education of China (No. 20120006110007)
文摘A spherical Fe matrix composite powder containing a high volume fraction （82vo1%） of fine TiC reinforcement was produced using a novel process combining in situ synthesis and plasma techniques. The composite powder exhibited good sphericity and a dense structure, and the fine sub-micron TiC particles were homogeneously distributed in the α-Fe matrix. A TiC-Fe cermet was prepared from the as-prepared spherical composite powder using powder metallurgy at a low sintering temperature; the product exhibited a hardness of HRA 88.5 and a flexural strength of 1360 MPa. The grain size of the fine-grained TiC and special surface structure of the spherical powder played the key roles in the fabrication process.
文摘The induced airfl w from passing trains,which is recognized as train wind,usually has adverse impacts on people in the surroundings,i.e.,the aerodynamic forces generated by a high-speed train＇s wind may act on the human body and endanger the safety of pedestrians or roadside workers.In this paper,an improved delayed detached eddy simulation（IDDES） method is used to study train wind.The effects of the affiliate components and train length on train wind are analyzed.The results indicate that the aff liated components and train length have no effect on train wind in the area in front of the leading nose.In the downstream and wake regions,the longitudinal train wind becomes stronger as the length of the train increases,while the transverse train wind is not affected.The presence of affiliate components strengthens the train wind in the near fiel of the train because of strong fl w solid interactions but has limited effects on train wind in the far field.
文摘钩状缺陷是影响搅拌摩擦搭接焊接头性能的重要因素.为了尽可能的避免钩状缺陷的产生,利用不扎透上板的方式对2024-T4铝合金进行焊接,重点分析不同转速下的接头横截面形貌及力学性能.结果表明,利用不扎透上板的方式所得搭接界面保持连续且主要呈水平方向分布.由于搅拌针长度较小,焊核区底部的宽度远大于搅拌针尖端直径,使有效连接宽度增加,导致搭接接头在承受拉剪载荷时呈拉伸断裂模式.与转速为500 r/min相比,600 r/min下接头的有效连接宽度与剪切拉伸强度均有小幅度地增加,最大剪切拉伸载荷为17 215.11 N.
