The effect of quenching rate on the aging precipitation behavior and properties of Al-Zn-Mg-Cu-Zr-Er alloy was investigated.The scanning electron microscopy,transmission electron microscopy,and atom probe tomography w...The effect of quenching rate on the aging precipitation behavior and properties of Al-Zn-Mg-Cu-Zr-Er alloy was investigated.The scanning electron microscopy,transmission electron microscopy,and atom probe tomography were used to study the characteristics of clusters and precipitates in the alloy.The quench-inducedηphase and a large number of clusters are formed in the air-cooled alloy with the slowest cooling rate,which contributes to an increment of hardness by 24%(HV 26)compared with that of the water-quenched one.However,the aging hardening response speed and peak-aged hardness of the alloy increase with the increase of quenching rate.Meanwhile,the water-quenched alloy after peak aging also has the highest strength,elongation,and corrosion resistance,which is due to the high driving force and increased number density of aging precipitates,and the narrowed precipitate free zones.展开更多
A nonlinear explicit dynamic finite element formulation based on the generalized beam theory(GBT)is proposed and developed to simulate the dynamic responses of prismatic thin-walled steel members under transverse impu...A nonlinear explicit dynamic finite element formulation based on the generalized beam theory(GBT)is proposed and developed to simulate the dynamic responses of prismatic thin-walled steel members under transverse impulsive loads.Considering the rate strengthening and thermal softening effects on member impact behavior,a modified Cowper-Symonds model for constructional steels is utilized.The element displacement field is built upon the superposition of GBT cross-section deformation modes,so arbitrary deformations such as cross-section distortions,local buckling and warping shear can all be involved by the proposed model.The amplitude function of each cross-section deformation mode is approximated by the cubic non-uniform B-spline basis functions.The Kirchhoff s thin-plate assumption is utilized in the construction of the bending related displacements.The Green-Lagrange strain tensor and the second Piola-Kirchhoff(PK2)stress tensor are employed to measure deformations and stresses at any material point,where stresses are assumed to be in plane-stress state.In order to verify the effectiveness of the proposed GBT model,three numerical cases involving impulsive loading of the thin-walled parts are given.The GBT results are compared with those of the Ls-Dyna shell finite element.It is shown that the proposed model and the shell finite element analysis has equivalent accuracy in displacement and stress.Moreover,the proposed model is much more computationally efficient and structurally clearer than the shell finite elements.展开更多
基金the financial supports from the National Natural Science Foundation of China(No.51871033)the Opening Project of State Key Laboratory for Advanced Metals and Materials,China(No.2020-ZD02)。
文摘The effect of quenching rate on the aging precipitation behavior and properties of Al-Zn-Mg-Cu-Zr-Er alloy was investigated.The scanning electron microscopy,transmission electron microscopy,and atom probe tomography were used to study the characteristics of clusters and precipitates in the alloy.The quench-inducedηphase and a large number of clusters are formed in the air-cooled alloy with the slowest cooling rate,which contributes to an increment of hardness by 24%(HV 26)compared with that of the water-quenched one.However,the aging hardening response speed and peak-aged hardness of the alloy increase with the increase of quenching rate.Meanwhile,the water-quenched alloy after peak aging also has the highest strength,elongation,and corrosion resistance,which is due to the high driving force and increased number density of aging precipitates,and the narrowed precipitate free zones.
基金The National Natural Science Foundation of China(No.51078229)the Specialized Research Fund for the Doctoral Program of Higher Education(o.20100073110008)
文摘A nonlinear explicit dynamic finite element formulation based on the generalized beam theory(GBT)is proposed and developed to simulate the dynamic responses of prismatic thin-walled steel members under transverse impulsive loads.Considering the rate strengthening and thermal softening effects on member impact behavior,a modified Cowper-Symonds model for constructional steels is utilized.The element displacement field is built upon the superposition of GBT cross-section deformation modes,so arbitrary deformations such as cross-section distortions,local buckling and warping shear can all be involved by the proposed model.The amplitude function of each cross-section deformation mode is approximated by the cubic non-uniform B-spline basis functions.The Kirchhoff s thin-plate assumption is utilized in the construction of the bending related displacements.The Green-Lagrange strain tensor and the second Piola-Kirchhoff(PK2)stress tensor are employed to measure deformations and stresses at any material point,where stresses are assumed to be in plane-stress state.In order to verify the effectiveness of the proposed GBT model,three numerical cases involving impulsive loading of the thin-walled parts are given.The GBT results are compared with those of the Ls-Dyna shell finite element.It is shown that the proposed model and the shell finite element analysis has equivalent accuracy in displacement and stress.Moreover,the proposed model is much more computationally efficient and structurally clearer than the shell finite elements.
