For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical prope...For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.展开更多
To investigate dynamic tensile and compressive properties of AT72 magnesium alloys under high strain rates,the Split Hopkinson tensile Bar(SHTB)and the Split Hopkinson Pressure Bar apparatus was used at ambient temper...To investigate dynamic tensile and compressive properties of AT72 magnesium alloys under high strain rates,the Split Hopkinson tensile Bar(SHTB)and the Split Hopkinson Pressure Bar apparatus was used at ambient temperature.The specimens after dynamic tension and dynamic compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties and fracture mechanism were discussed in this paper.The results show that at approximate tensile strain rate,the dynamic tensile strength of ordinary die-casting AT72 and vacuum die-casting AT72 is very similar,but the dynamic failure strain is of great difference.AT72 magnesium alloys under dynamic compressive yield continuously,and have the slight positive strain rate effect.The dynamic compressive behaviors of ordinary die-casting AT72 and vacuum die-casting AT72 are nearly the same.The dynamic tensile fracture mechanism of both vacuum die-casting AT72 and ordinary die-casting AT72 is inter-granular fracture.The dynamic compressive fracture mechanism of both vacuum die-casting AT72 and ordinary die-casting AT72 is quasi-cleavage intra-crystalline failure.The pores have an important effect on dynamic properties of die casting magnesium alloys.展开更多
We describe the target selection algorithm for the low latitude disk por- tion of the LAMOST Pilot Survey, which aims to test systems in preparation for the LAMOST spectroscopic survey. We use the PPMXL astrometric ca...We describe the target selection algorithm for the low latitude disk por- tion of the LAMOST Pilot Survey, which aims to test systems in preparation for the LAMOST spectroscopic survey. We use the PPMXL astrometric catalog, which provides positions, proper motions, B/R/I magnitudes (mostly) from USNO-B and d/H/Ks from the Two Micron All Sky Survey (2MASS) as well. We chose eight plates along the Galactic plane, in the region 0° 〈 α° 〈 67° and 42° 〈 δ 〈 59°, which cover 22 known open clusters with a range of ages. Adjacent plates may have some small overlapping area. Each plate covers an area of 2.5° in radius, with its cen- tral star (for the Shack-Hartmann guider) brighter than 8th magnitude. For each plate, we create an input catalog in the magnitude range 11.3 〈 Imag 〈 16.3 and Bmag available from PPMXL. The stars are selected to satisfy the requirements of the fiber positioning system and have a uniform distribution in the I vs. B - I color-magnitude diagram. Our final input catalog consists of 12 000 objects on each of eight plates that are observable during the winter observing season from the Xinglong Station of the National Astronomical Observatory of China.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51601154)the Fundamental Research Funds for the Central Universities, China (No. XDJK2019B003)+1 种基金the Natural Science Foundation of Jiangsu Higher Education Institutions of China (No. 17KJD430006)Chongqing Municipal Education Commission, China (No. KJZDK202001502)
基金The authors would like to acknowledge the financial support from the National Key Basic Research Program(973 Program),Project(2013CB632205).
文摘For the purpose of investigating the dynamic deformational behavior and failure mechanisms of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)was used for investigating dynamic mechanical properties of extruded Mg-Gd-Y Magnesium alloy at ambient temperature(300 K),200℃(473 K)and 300℃(573 K)temperature.The samples after compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties,crack performance and plastic deformation mechanism of extruded Mg-Gd-Y Magnesium alloy along the extrusion direction(ED)were discussed.The results show that,extruded Mg-Gd-Y Magnesium alloy has the largest dynamic compressive strength which is 535 MPa at ambient temperature(300 K)and strain rate of 2826 s^(−1).When temperature increases,dynamic compressive strength decreases,while ductility increases.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation and intergranular quasi-cleavage fracture at both ambient temperature and high temperature.The dynamic compressive deformation mechanism of extruded Mg-Gd-Y Magnesium alloy is a combination of twinning,slipping and dynamic recrystallization at both ambient temperature and high temperature.
基金The authors would like to acknowledge the financial support from the Ministry of Science and Technology of People’s Republic of China(National Basic Research Program of China,No:2011BAE22B05,Research and evaluation of magnesium alloy protection,connectivity and reliability)a Specialized Research Fund of the Doctoral Program of colleges and universities,No:20122102110002,Research of local deformation and fracture mechanism of AZ31 Magnesium alloy under high speed impact.
文摘To investigate dynamic tensile and compressive properties of AT72 magnesium alloys under high strain rates,the Split Hopkinson tensile Bar(SHTB)and the Split Hopkinson Pressure Bar apparatus was used at ambient temperature.The specimens after dynamic tension and dynamic compression were analyzed by scanning electron microscope(SEM)and metallographic microscope.Dynamic mechanical properties and fracture mechanism were discussed in this paper.The results show that at approximate tensile strain rate,the dynamic tensile strength of ordinary die-casting AT72 and vacuum die-casting AT72 is very similar,but the dynamic failure strain is of great difference.AT72 magnesium alloys under dynamic compressive yield continuously,and have the slight positive strain rate effect.The dynamic compressive behaviors of ordinary die-casting AT72 and vacuum die-casting AT72 are nearly the same.The dynamic tensile fracture mechanism of both vacuum die-casting AT72 and ordinary die-casting AT72 is inter-granular fracture.The dynamic compressive fracture mechanism of both vacuum die-casting AT72 and ordinary die-casting AT72 is quasi-cleavage intra-crystalline failure.The pores have an important effect on dynamic properties of die casting magnesium alloys.
基金funded by the National Natural Science Foundation of China (Grant Nos. 11173044(PI: Hou), 11073038 (PI: Chen), 10573022, 10973015 and 11061120454 (PI: Deng))the Key Project No.10833005 (PI: Hou)+2 种基金the Group Innovation Project No.11121062the US National Science Foundation grant AST 09-37523Chinese Academy of Sciences is acknowledged for providing initial support from grant number GJHZ 200812
文摘We describe the target selection algorithm for the low latitude disk por- tion of the LAMOST Pilot Survey, which aims to test systems in preparation for the LAMOST spectroscopic survey. We use the PPMXL astrometric catalog, which provides positions, proper motions, B/R/I magnitudes (mostly) from USNO-B and d/H/Ks from the Two Micron All Sky Survey (2MASS) as well. We chose eight plates along the Galactic plane, in the region 0° 〈 α° 〈 67° and 42° 〈 δ 〈 59°, which cover 22 known open clusters with a range of ages. Adjacent plates may have some small overlapping area. Each plate covers an area of 2.5° in radius, with its cen- tral star (for the Shack-Hartmann guider) brighter than 8th magnitude. For each plate, we create an input catalog in the magnitude range 11.3 〈 Imag 〈 16.3 and Bmag available from PPMXL. The stars are selected to satisfy the requirements of the fiber positioning system and have a uniform distribution in the I vs. B - I color-magnitude diagram. Our final input catalog consists of 12 000 objects on each of eight plates that are observable during the winter observing season from the Xinglong Station of the National Astronomical Observatory of China.