The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/stra...The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The one-step forward simulations of compression and rolling processes were presented as examples,and the results were compared with those obtained by classical incremental FE simulation to verify the feasibility and validity of the proposed method.展开更多
Nanotwinned diamond（nt-diamond）,which demonstrates unprecedented hardness and stability,is synthesized through the martensitic transformation of onion carbons at high pressure and high temperature（HPHT）.Its hardne...Nanotwinned diamond（nt-diamond）,which demonstrates unprecedented hardness and stability,is synthesized through the martensitic transformation of onion carbons at high pressure and high temperature（HPHT）.Its hardness and stability increase with decreasing twin thickness at the nanoscale.However,the formation mechanism of nanotwinning substructures within diamond nanograins is not well established.Here,we characterize the nanotwins in nt-diamonds synthesized under different HPHT conditions.Our observation shows that the nanotwin thickness reaches a minimum at ~20 GPa,below which phase-transformation twins and deformation twins coexist.Then,we use the density-functional-based tight-binding method and kinetic dislocation theory to investigate the subsequent plastic deformation mechanism in these pre-existing phase-transformation diamond twins.Our results suggest that pressure-dependent conversion of the plastic deformation mechanism occurs at a critical synthetic pressure for nt-diamond,which explains the existence of the minimum twin thickness.Our findings provide guidance on optimizing the synthetic conditions for fabricating nt-diamond with higher hardness and stability.展开更多
Pairing-deformation-frequency self-consistent cranking Woods-Saxon model is employed to investigate the triaxiality in the ground states of the neutron-rich even-even Mo, Ru isotopes. Deformation evolutions and transi...Pairing-deformation-frequency self-consistent cranking Woods-Saxon model is employed to investigate the triaxiality in the ground states of the neutron-rich even-even Mo, Ru isotopes. Deformation evolutions and transition probabilities have been studied, giving the triaxial shapes in their ground states. The kinematic moments of inertia have been calculated to illustrate the gradually rigid deformation. To understand the origin of the asymmetry shape in this region, we analyze the evolution of single-particle orbits with changing 3, deformation. The present calculations reveal the importance of the triaxial deformation in describing not only static property, but also rotational behaviors in this mass region, providing significant probes into the shell structure around.展开更多
基金Project(50575143)supported by the National Natural Science Foundation of ChinaProject(20040248005)supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘The bulk metal forming processes were simulated by using a one-step finite element(FE)approach based on deformation theory of plasticity,which enables rapid prediction of final workpiece configurations and stress/strain distributions.This approach was implemented to minimize the approximated plastic potential energy derived from the total plastic work and the equivalent external work in static equilibrium,for incompressibly rigid-plastic materials,by FE calculation based on the extremum work principle.The one-step forward simulations of compression and rolling processes were presented as examples,and the results were compared with those obtained by classical incremental FE simulation to verify the feasibility and validity of the proposed method.
基金supported by the National Natural Science Foundation of China(51421091,51332005,51572225,51272227, 51172197,51525205 and 51672239)the US National Science Foundation(EAR-1361276)
文摘Nanotwinned diamond（nt-diamond）,which demonstrates unprecedented hardness and stability,is synthesized through the martensitic transformation of onion carbons at high pressure and high temperature（HPHT）.Its hardness and stability increase with decreasing twin thickness at the nanoscale.However,the formation mechanism of nanotwinning substructures within diamond nanograins is not well established.Here,we characterize the nanotwins in nt-diamonds synthesized under different HPHT conditions.Our observation shows that the nanotwin thickness reaches a minimum at ~20 GPa,below which phase-transformation twins and deformation twins coexist.Then,we use the density-functional-based tight-binding method and kinetic dislocation theory to investigate the subsequent plastic deformation mechanism in these pre-existing phase-transformation diamond twins.Our results suggest that pressure-dependent conversion of the plastic deformation mechanism occurs at a critical synthetic pressure for nt-diamond,which explains the existence of the minimum twin thickness.Our findings provide guidance on optimizing the synthetic conditions for fabricating nt-diamond with higher hardness and stability.
基金supported by the National Key Basic Research Program of China(Grant No.2013CB834402)the National Natural Science Foundation of China(Grant Nos.11235001,11320101004 and 11575007)
文摘Pairing-deformation-frequency self-consistent cranking Woods-Saxon model is employed to investigate the triaxiality in the ground states of the neutron-rich even-even Mo, Ru isotopes. Deformation evolutions and transition probabilities have been studied, giving the triaxial shapes in their ground states. The kinematic moments of inertia have been calculated to illustrate the gradually rigid deformation. To understand the origin of the asymmetry shape in this region, we analyze the evolution of single-particle orbits with changing 3, deformation. The present calculations reveal the importance of the triaxial deformation in describing not only static property, but also rotational behaviors in this mass region, providing significant probes into the shell structure around.
