This study uses nonequilibrium molecular dynamics simulations to explore the dynamic failures and deformation mechanisms of a cylindrical shell composed of nanocrystalline nickel-titanium alloy under implosion loading...This study uses nonequilibrium molecular dynamics simulations to explore the dynamic failures and deformation mechanisms of a cylindrical shell composed of nanocrystalline nickel-titanium alloy under implosion loading.We discover that some individual spall planes are sequentially generated in the material along the propagation of a radial stress wave,indicative of the formation of multiple spallation.For larger grain sizes,void nucleation at the first spallation occurs in a coexisting intergranular/transgranular manner,whereas with decreasing grain size,voids tend to nucleate along the grain boundaries.Correspondingly,the spall strength exhibits a transition from an inverse Hall-Petch to a Hall-Petch relationship.For larger grain sizes,at the secondary spallation,localized shearing zones and grain boundaries provide potential void-nucleated sites.Importantly,the formation of shear deformation bands promotes grain refinement,contributing to a reduction in the dislocation-induced strengthening effect.Consequently,a lower spall strength is produced,in contrast to the first spallation.As the grain size becomes smaller,voids nucleate mostly along grain boundaries,and plastic deformation is dominated by dense grain boundaries.Overall,the high temperature caused by shear localization leads to material weakening,and in turn there is a significant decrease in the spall strength for the secondary spallation,compared with the first.Finally,significant penetration between two spall planes is observed for large grain size,which can be attributed to the nucleation of voids on linking grain boundaries,with temperatures exceeding the melting point of the material.展开更多
The beyond mean-field approach for low-lying hypernuclear states is extended by mixing the configurations associated with both single-particle and quadrupole-octupole collective excitations within the generator coordi...The beyond mean-field approach for low-lying hypernuclear states is extended by mixing the configurations associated with both single-particle and quadrupole-octupole collective excitations within the generator coordinate method based on a covariant den-sity functional theory.The method is demonstrated in the application to the low-lying states of 21ΛNe,where the configurations with theΛhyperon occupying the first(Λ_(s))and second(Λ_(p))lowest-energy states are considered.The results indicate that the positive-parity states are dominated by theα+^(12)C+α+Λ_(s) structure.In contrast,the low-lying negative-parity states are domi-nated by a strong admixture ofα+16O+Λ_(s) structure andα+12C+α+Λ_(p) structure due to the inclusion of octupole correlations.As a result,the low-lying negative-parity states become much lower than what is expected from the previous studies without the mixing,and the electric multipole transition strengths are significantly quenched.展开更多
We develop both relativistic mean field and beyond approaches for hypernuclei with possible quadrupole-octupole deformation or pear-like shapes based on relativistic point-coupling energy density functionals. The symm...We develop both relativistic mean field and beyond approaches for hypernuclei with possible quadrupole-octupole deformation or pear-like shapes based on relativistic point-coupling energy density functionals. The symmetries broken in the mean-field states are recovered with parity, particle-number and angular momentum projections. We take_Λ^(21)Ne as an example to illustrate the method, where the Λ hyperon is put on one of the two lowest-energy orbits(labeled as Λ_s, Λ_p), respectively. We find that the Λ hyperon in both cases disfavors the formation of a reflection-asymmetric molecular-like^(16)O+α structure in^(20)Ne, which is consistent with the Nilsson diagram for the hyperon in(β_2, β_3) deformation plane. In particular, we show that the negative-parity states with the configuration^(20)Ne(K~π= 0^-) Λ_s are close in energy to those with the configuration^(20)Ne(K~π= 0^+)Λ_p, even though they have very different structures. The Λ_s(Λ_p) becomes more and more concentrated around the bottom(top) of the"pear" with the increase of octupole deformation.展开更多
基金support of the National Natural Science Foundation of China under Grant Nos.12372367 and 12202081the Special Foundation from the Institute of Fluid Physics of CAEP under Grant No.2022-YCHT-0641.
文摘This study uses nonequilibrium molecular dynamics simulations to explore the dynamic failures and deformation mechanisms of a cylindrical shell composed of nanocrystalline nickel-titanium alloy under implosion loading.We discover that some individual spall planes are sequentially generated in the material along the propagation of a radial stress wave,indicative of the formation of multiple spallation.For larger grain sizes,void nucleation at the first spallation occurs in a coexisting intergranular/transgranular manner,whereas with decreasing grain size,voids tend to nucleate along the grain boundaries.Correspondingly,the spall strength exhibits a transition from an inverse Hall-Petch to a Hall-Petch relationship.For larger grain sizes,at the secondary spallation,localized shearing zones and grain boundaries provide potential void-nucleated sites.Importantly,the formation of shear deformation bands promotes grain refinement,contributing to a reduction in the dislocation-induced strengthening effect.Consequently,a lower spall strength is produced,in contrast to the first spallation.As the grain size becomes smaller,voids nucleate mostly along grain boundaries,and plastic deformation is dominated by dense grain boundaries.Overall,the high temperature caused by shear localization leads to material weakening,and in turn there is a significant decrease in the spall strength for the secondary spallation,compared with the first.Finally,significant penetration between two spall planes is observed for large grain size,which can be attributed to the nucleation of voids on linking grain boundaries,with temperatures exceeding the melting point of the material.
基金supported by the Science and Technology Project of Hebei Education Department(Grant No.ZC2021011)Scientific Research and Development Planning Project of Handan City(Grant No.21422901160)+5 种基金supported by the National Natural Science Foundation of China(Grant No.12005082)Jiangxi Provincial Natural Science Foun-dation(Grant No.20202BAB211008)Jiangxi Normal University(JXNU)Initial Research Foundation Grant to Doctor(Grant No.12019504)Young Talents Program under JXNU(Grant No.12019870)partially supported by the National Natural Science Foundation of China(Grant No.12141501)Fundamental Research Funds for Central Universities,Sun Yat-sen University.
文摘The beyond mean-field approach for low-lying hypernuclear states is extended by mixing the configurations associated with both single-particle and quadrupole-octupole collective excitations within the generator coordinate method based on a covariant den-sity functional theory.The method is demonstrated in the application to the low-lying states of 21ΛNe,where the configurations with theΛhyperon occupying the first(Λ_(s))and second(Λ_(p))lowest-energy states are considered.The results indicate that the positive-parity states are dominated by theα+^(12)C+α+Λ_(s) structure.In contrast,the low-lying negative-parity states are domi-nated by a strong admixture ofα+16O+Λ_(s) structure andα+12C+α+Λ_(p) structure due to the inclusion of octupole correlations.As a result,the low-lying negative-parity states become much lower than what is expected from the previous studies without the mixing,and the electric multipole transition strengths are significantly quenched.
基金supported by the National Natural Science Foundation of China(Grant No.11575148)the support by the Scientific Discovery through Advanced Computing(SciDAC)program funded by the U.S.Department of Energy,Office of Science,Office of Advanced Scientific Computing Research and Office of Nuclear Physics,under Award Number DE-SC0008641(NUCLEI SciDAC Collaboration)
文摘We develop both relativistic mean field and beyond approaches for hypernuclei with possible quadrupole-octupole deformation or pear-like shapes based on relativistic point-coupling energy density functionals. The symmetries broken in the mean-field states are recovered with parity, particle-number and angular momentum projections. We take_Λ^(21)Ne as an example to illustrate the method, where the Λ hyperon is put on one of the two lowest-energy orbits(labeled as Λ_s, Λ_p), respectively. We find that the Λ hyperon in both cases disfavors the formation of a reflection-asymmetric molecular-like^(16)O+α structure in^(20)Ne, which is consistent with the Nilsson diagram for the hyperon in(β_2, β_3) deformation plane. In particular, we show that the negative-parity states with the configuration^(20)Ne(K~π= 0^-) Λ_s are close in energy to those with the configuration^(20)Ne(K~π= 0^+)Λ_p, even though they have very different structures. The Λ_s(Λ_p) becomes more and more concentrated around the bottom(top) of the"pear" with the increase of octupole deformation.
