Compared to a cast AlSi10Mg alloy,a laser powder bed fused(LPBF)AlSi10Mg alloy shows superior yield strength and strain hardening capability.However,the underlying microstructure origin has not been comprehensively un...Compared to a cast AlSi10Mg alloy,a laser powder bed fused(LPBF)AlSi10Mg alloy shows superior yield strength and strain hardening capability.However,the underlying microstructure origin has not been comprehensively understood.In this work,the microstructural evolution of an LPBF AlSi10Mg alloy dur-ing tensile deformation was investigated.Synchrotron X-ray diffraction characterization shows that both stress and strain exhibit significant partition between an Al phase and a Si phase upon tensile deforma-tion.This leads to a significant strain gradient between those two phases,which is evident by the high density of dislocations in the cell boundaries of the deformed alloy.The strain gradient results in long-range internal stress,also known as back stress,in the cell boundaries,and in turn leads to enhanced strength and strain hardening in the LPBF AlSi10Mg alloy.Quantitatively analyses via loading-unloading-reloading tests show that during the tensile deformation,the back stress contributes 135 MPa to the yield strength of the alloy,which continuously increases with increasing the strain beyond the yielding point.This work illuminates the microstructural origin of the back stress in the LPBF AlSi10Mg alloy,i.e.the back stress arises from the stress/strain partition between the Al and Si phases in the cellular structures,and the back stress leads to significant strengthening of the alloy upon tensile deformation.This work may also provide guidance for manipulating the mechanical properties of additively manufactured Al-Si alloys for specific application needs.展开更多
In this paper, an approximate augmented Lagrangian function for nonlinear semidefinite programs is introduced. Some basic properties of the approximate augmented Lagrange function such as monotonicity and convexity ar...In this paper, an approximate augmented Lagrangian function for nonlinear semidefinite programs is introduced. Some basic properties of the approximate augmented Lagrange function such as monotonicity and convexity are discussed. Necessary and sufficient conditions for approximate strong duality results are derived. Conditions for an approximate exact penalty representation in the framework of augmented Lagrangian are given. Under certain conditions, it is shown that any limit point of a sequence of stationary points of approximate augmented Lagrangian problems is a KKT point of the original semidefinite program and that a sequence of optimal solutions to augmented Lagrangian problems converges to a solution of the original semidefinite program.展开更多
基金the National Key Research and Development Program(No.2022YFB3404203)the National Natural Science Foundation of China(Nos.52071262,52101049,52301197,52234009)+1 种基金the Qinchuangyuan"cientist+Engineer"Team Development of Shaanxi Province(No.2022KXJ-020)the Advanced Development of Aluminum Alloy Filler Materials used in welded High-end Lightweight Constructions-Research&Industrial implementation(No.2022Z109).
文摘Compared to a cast AlSi10Mg alloy,a laser powder bed fused(LPBF)AlSi10Mg alloy shows superior yield strength and strain hardening capability.However,the underlying microstructure origin has not been comprehensively understood.In this work,the microstructural evolution of an LPBF AlSi10Mg alloy dur-ing tensile deformation was investigated.Synchrotron X-ray diffraction characterization shows that both stress and strain exhibit significant partition between an Al phase and a Si phase upon tensile deforma-tion.This leads to a significant strain gradient between those two phases,which is evident by the high density of dislocations in the cell boundaries of the deformed alloy.The strain gradient results in long-range internal stress,also known as back stress,in the cell boundaries,and in turn leads to enhanced strength and strain hardening in the LPBF AlSi10Mg alloy.Quantitatively analyses via loading-unloading-reloading tests show that during the tensile deformation,the back stress contributes 135 MPa to the yield strength of the alloy,which continuously increases with increasing the strain beyond the yielding point.This work illuminates the microstructural origin of the back stress in the LPBF AlSi10Mg alloy,i.e.the back stress arises from the stress/strain partition between the Al and Si phases in the cellular structures,and the back stress leads to significant strengthening of the alloy upon tensile deformation.This work may also provide guidance for manipulating the mechanical properties of additively manufactured Al-Si alloys for specific application needs.
基金This work is partially supported by the Postdoctoral Fellowship of The Hong Kong Polytechnic Universitythe Research Grants Council of Hong Kong(PolyU B-Q890)
文摘In this paper, an approximate augmented Lagrangian function for nonlinear semidefinite programs is introduced. Some basic properties of the approximate augmented Lagrange function such as monotonicity and convexity are discussed. Necessary and sufficient conditions for approximate strong duality results are derived. Conditions for an approximate exact penalty representation in the framework of augmented Lagrangian are given. Under certain conditions, it is shown that any limit point of a sequence of stationary points of approximate augmented Lagrangian problems is a KKT point of the original semidefinite program and that a sequence of optimal solutions to augmented Lagrangian problems converges to a solution of the original semidefinite program.
