In this paper, single-walled carbon nanotubes (SWCNTs) are studied through molecular dynamics (MD) simulation. The simulations are performed at temperatures of 1 and 300K separately, with atomic interactions chara...In this paper, single-walled carbon nanotubes (SWCNTs) are studied through molecular dynamics (MD) simulation. The simulations are performed at temperatures of 1 and 300K separately, with atomic interactions characterized by the second Reactive Empirical Bond Order (REBO) potential, and temperature controlled by a certain thermostat, i.e. by separately using the velocity scaling, the Berendsen scheme, the Nose-Hoover scheme, and the generalized Langevin scheme. Results for a (5,5) SWCNT with a length of 24.5 nm show apparent distortions in nanotube configuration, which can further enter into periodic vibrations, except in simulations using the generalized Langevin thermostat, which is ascribed to periodic boundary conditions used in simulation. The periodic boundary conditions may implicitly be applied in the form of an inconsistent constraint along the axis of the nanotube. The combination of the inconsistent constraint with the cumulative errors in calculation causes the distortions of nanotubes. When the generalized Langevin thermostat is applied, inconsistently distributed errors are dispersed by the random forces, and so the distortions and vibrations disappear. This speculation is confirmed by simulation in the case without periodic boundary conditions, where no apparent distortion and vibration occur. It is also revealed that numerically induced distortions and vibrations occur only in simulation of nanotubes with a small diameter and a large length-to-diameter ratio. When MD simulation is applied to a system with a particular geometry, attention should be paid to avoiding the numerical distortion and the result infidelity.展开更多
The shape, type, content, and dimension of nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting were studied using scanning electron microscopy (SEM). The results show that the inclusions are m...The shape, type, content, and dimension of nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting were studied using scanning electron microscopy (SEM). The results show that the inclusions are mainly spherical Al2O3 and complex oxides composed of MnO, Al2O3 , and SiO2. The percentage of fine oxides smaller than 3 μm reaches up to 51.8%. The theoretical calculations show that fine oxides have precipitated during solidification. Therefore, it is concluded that during twin-roll strip casting, because of high cooling rate, the size of inclusions precipitated during solidification decreases, and the amount increases.展开更多
The solidification process of AISI 304 stainless steel during cooling at a rate of 0.05 K/s has been observed in situ using a confocal scanning laser microscope (CSLM). The results show that the 8 phase appeared fir...The solidification process of AISI 304 stainless steel during cooling at a rate of 0.05 K/s has been observed in situ using a confocal scanning laser microscope (CSLM). The results show that the 8 phase appeared first in liquid steel, as the temperature decreased, the γ phase precipitated prior at δ-grain boundary at 1452. 2 ℃, the liquid steel disappeared at 1 431.3 ℃, and then the γ phase precipitated on the δ ferrite. Based on the Scheil-Gulliver solidification model, the solidification processes of AISI 304 stainless steel are simulated using the Scheil model in Thermo Calc, and the simulation results agree well with the results observed in the experiment.展开更多
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No 20060003025)the State Key Program for Basic Research of China (Grant No 2003CB716201)
文摘In this paper, single-walled carbon nanotubes (SWCNTs) are studied through molecular dynamics (MD) simulation. The simulations are performed at temperatures of 1 and 300K separately, with atomic interactions characterized by the second Reactive Empirical Bond Order (REBO) potential, and temperature controlled by a certain thermostat, i.e. by separately using the velocity scaling, the Berendsen scheme, the Nose-Hoover scheme, and the generalized Langevin scheme. Results for a (5,5) SWCNT with a length of 24.5 nm show apparent distortions in nanotube configuration, which can further enter into periodic vibrations, except in simulations using the generalized Langevin thermostat, which is ascribed to periodic boundary conditions used in simulation. The periodic boundary conditions may implicitly be applied in the form of an inconsistent constraint along the axis of the nanotube. The combination of the inconsistent constraint with the cumulative errors in calculation causes the distortions of nanotubes. When the generalized Langevin thermostat is applied, inconsistently distributed errors are dispersed by the random forces, and so the distortions and vibrations disappear. This speculation is confirmed by simulation in the case without periodic boundary conditions, where no apparent distortion and vibration occur. It is also revealed that numerically induced distortions and vibrations occur only in simulation of nanotubes with a small diameter and a large length-to-diameter ratio. When MD simulation is applied to a system with a particular geometry, attention should be paid to avoiding the numerical distortion and the result infidelity.
基金This work was financially supported by the National Natural Science Foundation of China (No.50434040).
文摘The shape, type, content, and dimension of nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting were studied using scanning electron microscopy (SEM). The results show that the inclusions are mainly spherical Al2O3 and complex oxides composed of MnO, Al2O3 , and SiO2. The percentage of fine oxides smaller than 3 μm reaches up to 51.8%. The theoretical calculations show that fine oxides have precipitated during solidification. Therefore, it is concluded that during twin-roll strip casting, because of high cooling rate, the size of inclusions precipitated during solidification decreases, and the amount increases.
基金Item Sponsored by National Natural Science Foundation of China(50434040)
文摘The solidification process of AISI 304 stainless steel during cooling at a rate of 0.05 K/s has been observed in situ using a confocal scanning laser microscope (CSLM). The results show that the 8 phase appeared first in liquid steel, as the temperature decreased, the γ phase precipitated prior at δ-grain boundary at 1452. 2 ℃, the liquid steel disappeared at 1 431.3 ℃, and then the γ phase precipitated on the δ ferrite. Based on the Scheil-Gulliver solidification model, the solidification processes of AISI 304 stainless steel are simulated using the Scheil model in Thermo Calc, and the simulation results agree well with the results observed in the experiment.