The morphology and dimension of W phases play an important role in determining mechanical properties of Mg-RE-Zn(where RE denotes rare earth elements)alloys.In this study,theγ′platelet and W particle occurred in the...The morphology and dimension of W phases play an important role in determining mechanical properties of Mg-RE-Zn(where RE denotes rare earth elements)alloys.In this study,theγ′platelet and W particle occurred in the aged Mg-2Dy-0.5Zn(at.%)alloys were investigated by aberration-corrected scanning transmission electron microscopy.A novel formation mechanism of W phase was proposed,and its effects on the morphology and dimension of W particle,as well as mechanical properties of Mg-2Dy-0.5Zn alloys,were also discussed particularly.Different from other Mg-RE-Zn alloys,the nucleation and growth of W particle in Mg-Dy-Zn alloys mainly depend on the precipitatedγ′platelet.Primarily,a mass of Dy and Zn solute atoms concentrated nearγ′platelet or between two adjacentγ′platelets can meet the composition requirement of W particle nucleation.Next,the smaller interfacial mismatch between W andγ′facilitates the nucleation and growth of W particle.Thirdly,the growth of W particle can be achieved by consuming the surroundingγ′platelets.The nucleation and growth mechanisms make W particles exhibit rectangular or leaf-like and remain at the nanoscale.The coexistence ofγ′platelets and nanoscale W particles,and some better interfacial relationships between phases,lead to a high strength-ductility synergy of alloy.The findings may provide some fundamental guidelines for the microstructure design and optimization of new-type Mg-based alloys.展开更多
We further consider the effect of rod strength by employing the compressible penetration model to study the effect of compressibility on hypervelocity penetration.Meanwhile, we define different instances of penetratio...We further consider the effect of rod strength by employing the compressible penetration model to study the effect of compressibility on hypervelocity penetration.Meanwhile, we define different instances of penetration efficiency in various modified models and compare these penetration efficiencies to identify the effects of different factors in the compressible model. To systematically discuss the effect of compressibility in different metallic rod-target combinations, we construct three cases, i.e., the penetrations by the more compressible rod into the less compressible target, rod into the analogously compressible target, and the less compressible rod into the more compressible target. The effects of volumetric strain, internal energy, and strength on the penetration efficiency are analyzed simultaneously. It indicates that the compressibility of the rod and target increases the pressure at the rod/target interface. The more compressible rod/target has larger volumetric strain and higher internal energy. Both the larger volumetric strain and higher strength enhance the penetration or anti-penetration ability. On the other hand, the higher internal energy weakens the penetration or anti-penetration ability. The two trends conflict, but the volumetric strain dominates in the variation of the penetration efficiency, which would not approach the hydrodynamic limit if the rod and target are not analogously compressible. However, if the compressibility of the rod and target is analogous, it has little effect on the penetration efficiency.展开更多
Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical,automobile,aerospace including defence technology.Variety of modelling techniques have been a...Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical,automobile,aerospace including defence technology.Variety of modelling techniques have been adopted in the past to model mechanical behaviour of particulate composites.Due to their favourable properties,particle-based methods provide a convenient platform to model failure or fracture of these composites.Smooth particle hydrodynamics(SPH)is one of such methods which demonstrate excellent potential for modelling failure or fracture of particulate composites in a Lagrangian setting.One of the major challenges in using SPH method for modelling composite materials depends on accurate and efficient way to treat interface and boundary conditions.In this paper,a masterslave method based multi-freedom constraints is proposed to impose essential boundary conditions and interfacial displacement constraints in modelling mechanical behaviour of composite materials using SPH method.The proposed methodology enforces the above constraints more accurately and requires only smaller condition number for system stiffness matrix than the procedures based on typical penalty function approach.A minimum cut-off value-based error criteria is employed to improve the computational efficiency of the proposed methodology.In addition,the proposed method is further enhanced by adopting a modified numerical interpolation scheme along the boundary to increase the accuracy and computational efficiency.The numerical examples demonstrate that the proposed master-slave approach yields better accuracy in enforcing displacement constraints and requires approximately the same computational time as that of penalty method.展开更多
1.Introduction High strength steels continue to be developed for automotive applications to increase safety and reduce lightweight by downgauging[1,2].In addition,reducing density is another solution for the lightweig...1.Introduction High strength steels continue to be developed for automotive applications to increase safety and reduce lightweight by downgauging[1,2].In addition,reducing density is another solution for the lightweight of automotive components[3,4].Aluminum addition could effectively reduce the density of steels,since it has a low atomic mass and invokes a lattice expansion[5].展开更多
1.Introduction The precipitation of κ-carbides is critical for the deformation behavior of Fe-Mn-Al-C austenitic low-density steels[1-5].Ther-momechanical treatment can significantly influence the distribution,size,a...1.Introduction The precipitation of κ-carbides is critical for the deformation behavior of Fe-Mn-Al-C austenitic low-density steels[1-5].Ther-momechanical treatment can significantly influence the distribution,size,and morphology of κ-carbides,and thus regulate the mechanical properties[1,4,6-8].Intragranular κ-carbides precipitate through either nucleation and growth mechanisms[9]or spinodal decomposition[3,5],depending on thermodynamic conditions.展开更多
The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of...The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of 0.5×10^(35) cm^(–2)·s^(–1) or higher.The STCF will produce a data sample about a factor of 100 larger than that of the presentτ-charm factory—the BEPCII,providing a unique platform for exploring the asymmetry of matter-antimatter(charge-parity violation),in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions,as well as searching for exotic hadrons and physics beyond the Standard Model.The STCF project in China is under development with an extensive R&D program.This document presents the physics opportunities at the STCF,describes conceptual designs of the STCF detector system,and discusses future plans for detector R&D and physics case studies.展开更多
1 Introduction Ring Opening Metathesis Polymerization(ROMP)is based on the olefin metathesis reaction,which requires transition metal catalysts.Mainly molybdenum,tungsten and ruthenium based catalysts have up to now b...1 Introduction Ring Opening Metathesis Polymerization(ROMP)is based on the olefin metathesis reaction,which requires transition metal catalysts.Mainly molybdenum,tungsten and ruthenium based catalysts have up to now been used.The“in-between”metal rhenium was only rarely applied in olefin metathesis reactions,and not at all in ROMP processes.We have found that cationic phosphine substituted dinitrosyl rhenium complexes 1a and 1b effectively catalyze ROMP of norbonene,dicyclopentadiene and of cyclooctene.See Fig.1.展开更多
基金supported by Natural Science Foundation of Liaoning Province of China under Grant No.2020-MS-085。
文摘The morphology and dimension of W phases play an important role in determining mechanical properties of Mg-RE-Zn(where RE denotes rare earth elements)alloys.In this study,theγ′platelet and W particle occurred in the aged Mg-2Dy-0.5Zn(at.%)alloys were investigated by aberration-corrected scanning transmission electron microscopy.A novel formation mechanism of W phase was proposed,and its effects on the morphology and dimension of W particle,as well as mechanical properties of Mg-2Dy-0.5Zn alloys,were also discussed particularly.Different from other Mg-RE-Zn alloys,the nucleation and growth of W particle in Mg-Dy-Zn alloys mainly depend on the precipitatedγ′platelet.Primarily,a mass of Dy and Zn solute atoms concentrated nearγ′platelet or between two adjacentγ′platelets can meet the composition requirement of W particle nucleation.Next,the smaller interfacial mismatch between W andγ′facilitates the nucleation and growth of W particle.Thirdly,the growth of W particle can be achieved by consuming the surroundingγ′platelets.The nucleation and growth mechanisms make W particles exhibit rectangular or leaf-like and remain at the nanoscale.The coexistence ofγ′platelets and nanoscale W particles,and some better interfacial relationships between phases,lead to a high strength-ductility synergy of alloy.The findings may provide some fundamental guidelines for the microstructure design and optimization of new-type Mg-based alloys.
文摘We further consider the effect of rod strength by employing the compressible penetration model to study the effect of compressibility on hypervelocity penetration.Meanwhile, we define different instances of penetration efficiency in various modified models and compare these penetration efficiencies to identify the effects of different factors in the compressible model. To systematically discuss the effect of compressibility in different metallic rod-target combinations, we construct three cases, i.e., the penetrations by the more compressible rod into the less compressible target, rod into the analogously compressible target, and the less compressible rod into the more compressible target. The effects of volumetric strain, internal energy, and strength on the penetration efficiency are analyzed simultaneously. It indicates that the compressibility of the rod and target increases the pressure at the rod/target interface. The more compressible rod/target has larger volumetric strain and higher internal energy. Both the larger volumetric strain and higher strength enhance the penetration or anti-penetration ability. On the other hand, the higher internal energy weakens the penetration or anti-penetration ability. The two trends conflict, but the volumetric strain dominates in the variation of the penetration efficiency, which would not approach the hydrodynamic limit if the rod and target are not analogously compressible. However, if the compressibility of the rod and target is analogous, it has little effect on the penetration efficiency.
基金National Key R&D Program of China(No.2018YFC0809700,No.2017YFC0803300)National Natural Science Foundation of China(No.71673158,No.11702046).
文摘Particulate composites are one of the widely used materials in producing numerous state-of-the-art components in biomedical,automobile,aerospace including defence technology.Variety of modelling techniques have been adopted in the past to model mechanical behaviour of particulate composites.Due to their favourable properties,particle-based methods provide a convenient platform to model failure or fracture of these composites.Smooth particle hydrodynamics(SPH)is one of such methods which demonstrate excellent potential for modelling failure or fracture of particulate composites in a Lagrangian setting.One of the major challenges in using SPH method for modelling composite materials depends on accurate and efficient way to treat interface and boundary conditions.In this paper,a masterslave method based multi-freedom constraints is proposed to impose essential boundary conditions and interfacial displacement constraints in modelling mechanical behaviour of composite materials using SPH method.The proposed methodology enforces the above constraints more accurately and requires only smaller condition number for system stiffness matrix than the procedures based on typical penalty function approach.A minimum cut-off value-based error criteria is employed to improve the computational efficiency of the proposed methodology.In addition,the proposed method is further enhanced by adopting a modified numerical interpolation scheme along the boundary to increase the accuracy and computational efficiency.The numerical examples demonstrate that the proposed master-slave approach yields better accuracy in enforcing displacement constraints and requires approximately the same computational time as that of penalty method.
基金supported by the National Natural Science Foundation of China[grant numbers 5180407251722402]+3 种基金the Fundamental Research Funds for the Central Universities[grant number N2007012]the China Postdoctoral Science Foundation[grant number 2018M631802]the 111 Project[grant number B16009]the Liaoning Revitalization Talent Program[grant number xlyc1907128]。
文摘1.Introduction High strength steels continue to be developed for automotive applications to increase safety and reduce lightweight by downgauging[1,2].In addition,reducing density is another solution for the lightweight of automotive components[3,4].Aluminum addition could effectively reduce the density of steels,since it has a low atomic mass and invokes a lattice expansion[5].
基金financially supported by the National Natural Science Foundation of China(grant No 52171108)the Natural Science Foundation of Liaoning Province(grant No 2023-MSBA-037)the Fundamental Research Funds for the Central University(grant No N2402007).
文摘1.Introduction The precipitation of κ-carbides is critical for the deformation behavior of Fe-Mn-Al-C austenitic low-density steels[1-5].Ther-momechanical treatment can significantly influence the distribution,size,and morphology of κ-carbides,and thus regulate the mechanical properties[1,4,6-8].Intragranular κ-carbides precipitate through either nucleation and growth mechanisms[9]or spinodal decomposition[3,5],depending on thermodynamic conditions.
基金supported by the National Key R&D Program of China under Contract No.2022YFA1602200the International Partnership Program of the Chineses Academy of Sciences under Grant No.211134KYSB20200057the STCF Key Technology Research and Development Project.
文摘The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of 0.5×10^(35) cm^(–2)·s^(–1) or higher.The STCF will produce a data sample about a factor of 100 larger than that of the presentτ-charm factory—the BEPCII,providing a unique platform for exploring the asymmetry of matter-antimatter(charge-parity violation),in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions,as well as searching for exotic hadrons and physics beyond the Standard Model.The STCF project in China is under development with an extensive R&D program.This document presents the physics opportunities at the STCF,describes conceptual designs of the STCF detector system,and discusses future plans for detector R&D and physics case studies.
文摘1 Introduction Ring Opening Metathesis Polymerization(ROMP)is based on the olefin metathesis reaction,which requires transition metal catalysts.Mainly molybdenum,tungsten and ruthenium based catalysts have up to now been used.The“in-between”metal rhenium was only rarely applied in olefin metathesis reactions,and not at all in ROMP processes.We have found that cationic phosphine substituted dinitrosyl rhenium complexes 1a and 1b effectively catalyze ROMP of norbonene,dicyclopentadiene and of cyclooctene.See Fig.1.
