First-principles methods based on density functional theory(DFT)are nowadays routinely applied to calculate the elastic constants of materials at temperature of 0 K.Nevertheless,the first-principles calculations of el...First-principles methods based on density functional theory(DFT)are nowadays routinely applied to calculate the elastic constants of materials at temperature of 0 K.Nevertheless,the first-principles calculations of elastic constants at finite temperature are not straightforward.In the present work,the feasibility of the ab initio molecular dynamic(AIMD)method in calculations of the temperature dependent elastic constants of relatively"soft"metals,taking face centered cubic(FCC)aluminum(Al)as example,is explored.The AIMD calculations are performed with carefully selected strain tensors and strain magnitude.In parallel with the AIMD calculations,first-principles calculations with the quasiharmonic approximation(QHA)are performed as well.We show that all three independent elastic constant components(C11,C12 and C44)of Al from both the AIMD and QHA calculations decrease with increasing temperature T,in good agreement with those from experimental measurements.Our work allows us to quantify the individual contributions of the volume expansion,lattice vibration(excluding those contributed to the volume expansion),and electronic temperature effects to the temperature induced variation of the elastic constants.For Al with stable FCC crystal structure,the volume expansion effect contributes the major part(about 75%~80%)in the temperature induced variation of the elastic constants.The contribution of the lattice vibration is minor(about 20%~25%)while the electronic temperature effect is negligible.Although the elastic constants soften with increasing temperature,FCC Al satisfies the Born elastic stability criteria with temperature up to the experimental melting point.展开更多
The mechanical and microstructural properties as well as crystallographic textures of asymmetrically rolled low carbon steel were studied.The modelling of plastic deformation was carried out in two scales:in the macro...The mechanical and microstructural properties as well as crystallographic textures of asymmetrically rolled low carbon steel were studied.The modelling of plastic deformation was carried out in two scales:in the macro-scale,using the finite elements method,and in the crystallographic scale,using the polycrystalline deformation model.The internal stress distribution in the rolling gap was calculated using the finite elements method and these stresses were then applied to the polycrystalline elasto-plastic deformation model.Selected mechanical properties,namely residual stress distribution,deformation work,applied force and torques,and bend amplitude,were calculated.The diffraction measurements,X-ray and electron backscatter diffraction,enabled the examination of texture heterogeneity and selected microstructure characteristics.The predicted textures agree well with those determined experimentally.The plastic anisotropy of cold rolled ferritic steel samples,connected with texture,was expressed by Lankford coefficient.展开更多
Castellation of plasma facing components is foreseen as the best solution for ensuring the lifetime of future fusion devices. However, the gaps between the resulting surface elements can increase fuel retention and co...Castellation of plasma facing components is foreseen as the best solution for ensuring the lifetime of future fusion devices. However, the gaps between the resulting surface elements can increase fuel retention and complicate fuel removal issues. To know how the fuel is retained inside the gaps, the plasma sheath around the gaps needs to be understood first. In this work, a kinetic model is used to study plasma characteristics around the divertor gaps with the focus on the H＋ penetration depth inside the poloidal gaps, and a rate-theory model is coupled to simulate the hydrogen retention inside the tungsten gaps. By varying the magnetic field strength and plasma temperature, we find that the H＋ cyclotron radius has a significant effect on the penetration depth. Besides, the increase of magnetic field inclination angle can also increase the penetration depth. It is found in this work that parameters as well as the penetration depth strongly affect fuel retention in tungsten gaps.展开更多
基金the National Key Research and Development Program of China(No.2016YFB0701301)the National Nature Science Foundation of China(No.91860107)the National Key Basic Research Program(No.2014CB644001)。
文摘First-principles methods based on density functional theory(DFT)are nowadays routinely applied to calculate the elastic constants of materials at temperature of 0 K.Nevertheless,the first-principles calculations of elastic constants at finite temperature are not straightforward.In the present work,the feasibility of the ab initio molecular dynamic(AIMD)method in calculations of the temperature dependent elastic constants of relatively"soft"metals,taking face centered cubic(FCC)aluminum(Al)as example,is explored.The AIMD calculations are performed with carefully selected strain tensors and strain magnitude.In parallel with the AIMD calculations,first-principles calculations with the quasiharmonic approximation(QHA)are performed as well.We show that all three independent elastic constant components(C11,C12 and C44)of Al from both the AIMD and QHA calculations decrease with increasing temperature T,in good agreement with those from experimental measurements.Our work allows us to quantify the individual contributions of the volume expansion,lattice vibration(excluding those contributed to the volume expansion),and electronic temperature effects to the temperature induced variation of the elastic constants.For Al with stable FCC crystal structure,the volume expansion effect contributes the major part(about 75%~80%)in the temperature induced variation of the elastic constants.The contribution of the lattice vibration is minor(about 20%~25%)while the electronic temperature effect is negligible.Although the elastic constants soften with increasing temperature,FCC Al satisfies the Born elastic stability criteria with temperature up to the experimental melting point.
基金Projects(DEC-2011/01/B/ST8/07394,DEC-2011/01/D/ST8/07399)supported by the Polish National Centre for Science(NCN)The support of the Polish Ministry of Science and Higher Education and of the French ANR 05-BLAN-0383 project
文摘The mechanical and microstructural properties as well as crystallographic textures of asymmetrically rolled low carbon steel were studied.The modelling of plastic deformation was carried out in two scales:in the macro-scale,using the finite elements method,and in the crystallographic scale,using the polycrystalline deformation model.The internal stress distribution in the rolling gap was calculated using the finite elements method and these stresses were then applied to the polycrystalline elasto-plastic deformation model.Selected mechanical properties,namely residual stress distribution,deformation work,applied force and torques,and bend amplitude,were calculated.The diffraction measurements,X-ray and electron backscatter diffraction,enabled the examination of texture heterogeneity and selected microstructure characteristics.The predicted textures agree well with those determined experimentally.The plastic anisotropy of cold rolled ferritic steel samples,connected with texture,was expressed by Lankford coefficient.
基金supported by the National Magnetic Confinement Fusion Science Program,China(Grant No.2013GB109001)the National Natural Science Foundation of China(Grant Nos.11275042 and 11305026)the Fundamental Research Funds for the Central Universities of Ministry of Education of China(Grant No.DUT14RC(3)039)
文摘Castellation of plasma facing components is foreseen as the best solution for ensuring the lifetime of future fusion devices. However, the gaps between the resulting surface elements can increase fuel retention and complicate fuel removal issues. To know how the fuel is retained inside the gaps, the plasma sheath around the gaps needs to be understood first. In this work, a kinetic model is used to study plasma characteristics around the divertor gaps with the focus on the H＋ penetration depth inside the poloidal gaps, and a rate-theory model is coupled to simulate the hydrogen retention inside the tungsten gaps. By varying the magnetic field strength and plasma temperature, we find that the H＋ cyclotron radius has a significant effect on the penetration depth. Besides, the increase of magnetic field inclination angle can also increase the penetration depth. It is found in this work that parameters as well as the penetration depth strongly affect fuel retention in tungsten gaps.
