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Acta Metallurgica Sinica(English Letters) 2016年第6期29卷 561-567页

作者： Chi zhang li-wen zhang Zhen-Yu liu School of Materials Science and Engineering Dalian University of Technology State Key Lab of Rolling Technologies and Automation Northeastern University

The effects of the finisher entry temperatures（FETs） on the surface ridging behavior for an ultra-purified21%Cr ferritic stainless steel have been investigated. The results indicate that decreasing the FET facilitates the formation of in-grain shear bands in the hot rolled slab. The in-grain shear bands supplied recrystallization nucleation sites in grains during subsequent annealing through coalescence of subgrains, which is beneficial to refine the microstructures and intensify the {111}//ND textures. This effect will evolve to the final cold rolled and annealed sheet. The micro-texture analysis indicates that the formation of grain colony in the final sheet is weakened by decreasing the FET. Then, the surface ridging resistance of FSS is enhanced due to the optimizing of micro-texture distribution.

关键词： Ferritic steels Surface ridging Micro-texture Electron backscattered diffraction(EBSD)

Estimating Restricted Common Structural Changes for Panel Data

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Acta Mathematicae Applicatae Sinica 2019年第4期35卷 893-908页

作者： li-wen zhang Zhong-yi ZHU School of Statistics and Management Shanghai University of Finance and Economics Shanghai 200444 China Department of Statistics School of Management Fudan University Shanghai 200433 China

We consider estimating multiple structural changes occurring at unknown common dates in a panel data regression model with restrictions imposed on the coefficients. We establish the consistency and rate of convergence of the structural change estimates and the asymptotic distribution of the parameter *** is shown that the efficiency of the parameter estimators is increased using the restrictions. An efficient dynamic algorithm is proposed to obtain the break date estimates and the parameter estimates. In addition, we propose a testing procedure for the existence of the change points with the restrictions and derive the asymptotic distribution under the null hypothesis of the test statistics. Simulation studies are presented to investigate the performance of the proposed method in finite samples.

关键词： common structural changes panel data consistency

Numerical simulation on recrystallization behavior and microstructure evolution during hot continuous rolling process of 38CrMoAl steel rod

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Journal of Iron and Steel Research International 2022年第10期29卷 1633-1645页

作者： Fei li li-wen zhang Chi zhang Kang-jie Song Pei-gang Mao School of Materials Science and Engineering Dalian University of TechnologyDalian116024LiaoningChina

The control of microstructure during hot rolling process of steel is of great importance and will affect the properties of the steel *** to the production line,a three-dimensional multi-field coupled finite element model of 24-pass continuous hot rolling process of 38CrMoAl steel rod is established using the finite element software *** on the recrystallization kinetics model and the grain growth model,a subroutine written in Fortran is introduced to calculate the recrystallization behavior and microstructure evolution of 38CrMoAl steel during the entire rolling *** distribution and evolution of variables such as strain,temperature and recrystallization fractions during the rolling process are *** temperature variations and grain sizes at both the center and surface of the tested steel are compared with the experimental *** it is found that the simulation results are in good agreement with the experimental ones,confirming the reliability of the established model.

关键词： 38CrMoAl steel Recrystallization Microstructure evolution Hot rolling process Numerical simulation

Applications of molten salt and progress of molten salt electrolysis in secondary metal resource recovery

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International Journal of Minerals,Metallurgy and Materials 2020年第12期27卷 1599-1617页

作者： Xiao-li Ming Feng li-wen zhang Zuo-ren Nie College of Materials Science and Engineering Key Laboratory of Advanced Functional MaterialsEducation Ministry of ChinaBeijing University of TechnologyBeijing 100124China National Engineering Laboratory for Industrial Big-data Application Technology Beijing University of TechnologyBeijing 100124China

Molten salt is an excellent medium for chemical reaction,energy transfer,and *** salt innovative technologies should be developed to recover metals from secondary resources and reserve metals from primary natural *** these technologies,molten salt electrolysis is an economic and environment-friendly method to extract metals from waste *** the perspective of molten salt characteristics,the application of molten salts in chemistry,electrochemistry,energy,and thermal storage should be comprehensively *** review discusses further directions for the research and development of molten salt electrolysis and their use for metal recovery from various metal wastes,such as magnet scrap,nuclear waste,and cemented carbide *** is placed on the development of various electrolysis methods for different metal containing wastes,overcoming some problems in electrolytes,electrodes,and electrolytic *** focus is given to future development directions for current associated processing obstacles.

关键词： molten salt application molten salt electrochemistry resource recycling cemented carbide scrap

On Ekeland's Variational Principle for Set-Valued Mappings

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Acta Mathematicae Applicatae Sinica 2007年第1期23卷 141-148页

作者： Sheng-jie li wen-yan zhang College of Mathematics and Science Chongqing University Chongqing 400044 China

In this paper, we derive a general vector Ekeland variational principle for set-valued mappings, which has a dosed relation to εk^0 -efficient points of set-valued optimization problems. The main result presented in ... 详细信息

关键词： Vector Ekeland variational principle nonlinear scalarization function metric space set-valued mapping

On the Finite Convergence of Newton-type Methods for P_0 Affine Variational Inequalities

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Acta Mathematica Sinica,English Series 2007年第9期23卷 1553-1562页

作者： li Ping zhang wen Xun XING Department of Mathematical Sciences Tsinghua University Beijing 100084 P. R. China

Based on the techniques used in non-smooth Newton methods and regularized smoothing Newton methods, a Newton-type algorithm is proposed for solving the P0 affine variational inequality problem. Under mild conditions, the algorithm can find an exact solution of the P0 affine variational inequality problem in finite steps. Preliminary numerical results indicate that the algorithm is promising.

关键词： affine variational inequality non-smooth smoothing Newton method finite termination

Testing for Change Points in Partially linear Models

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Acta Mathematicae Applicatae Sinica 2015年第4期31卷 879-892页

作者： li-wen zhang Zhong-yi ZHU School of Economics Shanghai University Department of Statistics School of ManagementFudan University

In this paper we provide a method to test the existence of the change points in the nonparametric regression function of partially linear models with conditional heteroscedastic variance. We propose the test statistic and establish its asymptotic properties under some regular conditions. Some simulation studies are given to investigate the performance of the proposed method in finite samples. Finally, the proposed method is applied to a real data for illustration.

关键词： change point partially linear model heteroscedastic variance local linear regression bandwidthselection

3D Crystal Plasticity Finite Element Modeling of the Tensile Deformation of Polycrystalline Ferritic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2017年第1期30卷 79-88页

作者： Chi zhang li-wen zhang wen-Fei Shen Ying-Nan Xia Yu-Tan Yan School of Materials Science and Engineering Dalian University of TechnologyDalian 116024China

A mesoscale model of plastic deformation of ferritic stainless steels （FSSs） is formulated by combining a crystal plasticity finite element model with 3D cellular automaton algorithm. The actual grain orientations of FSS cold rolling and annealing sheet have been detected by electron backscatter diffraction and selected to be assigned to the polycrystal model. The simulation results have been validated by comparing the calculated true stress-strain response with the experimental one. For the lack of considering the interactions of dislocations with impurities, there are no upper and lower yield points in the simulation stress-strain curves. However, the calculated yield strength and the stress-strain response after yielding agree well with the real material. The local stress and strain fields show inhomogeneous at mesoscale. The plastic deformations of the grains with typical orientations have been characterized. The analysis reveals that the grains with fiber texture show higher thickness reduction ratio as compared to others. The deformation behaviors of the grains in polycrystal are not only related to the orientations but also to the interactions from adjacent grains.

关键词： Ferritic steels Crystallographic orientation Polycrystal plasticity modeling Cellular automaton

Photogalvanic effect induced charge and spin photocurrent in group-V monolayer systems

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Frontiers of physics 2023年第6期18卷 253-261页

作者： li-wen zhang Ya-Qing Yang Jun Chen Lei zhang School of Physics and Information Engineering Shanxi Normal UniversityTaiyuan 030031China State Key Laboratory of Quantum Optics and Quantum Optics Devices Institute of Laser SpectroscopyShanxi UniversityTaiyuan 030006China State Key Laboratory of Quantum Optics and Quantum Optics Devices Institute of Theoretical PhysicsShanxi UniversityTaiyuan 030006China Collaborative Innovation Center of Extreme Optics Shanxi UniversityTaiyuan 030006China

Photogalvanic effect(PGE)occurs in materials with non-centrosymmetric structures when irradiated by linearly or circularly polarized ***,using non-equilibrium Green’s function combined with density functional theory(NEGF-DFT),we investigated the linear photogalvanic effect(LPGE)in monolayers of group-V elements(As,Sb,and Bi)by first-principles ***,by designing a two-probe structure based on the group-V elements,we found a giant anisotropy photoresponse of As between the armchair and zigzag ***,we analyzed Sb and Bi’s charge and spin photocurrent characteristics when considering the spin-orbit coupling(SOC)*** is found that when the polarization direction of linearly polarized light is parallel or perpendicular to the transport direction(θ=0°or 90°),the spin up and spin down photoresponse in the armchair direction has the same magnitude and direction,leading to the generation of net charge ***,in the zigzag direction,the spin up and spin down photoresponse have the same magnitude with opposite directions,leading to the generation of pure spin ***,it is understood by analyzing the bulk spin photovoltaic(BSPV)coefficient from the symmetry point of ***,we found that the net charge current generated in the armchair direction and the pure spin current generated in the zigzag direction can be further tuned with the increase of the material’s buckling *** results highlight that these group-V monolayers are promising candidates for novel functional materials,which will provide a broad prospect for the realization of ultrathin ferroelectric devices in optoelectronics due to their spontaneous polarization characteristics and high Curie temperature.

关键词： group-V monolayers photogalvanic effect pure spin current

Microstructures and properties evolution of Al-Zn-Mg-Cu alloy under electrical pulse assisted creep aging

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Advances in Manufacturing 2022年第4期10卷 596-609页

作者： Tian-Jun Bian Heng li Chao Lei Chang-Hui Wu li-wen zhang State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an710072People’s Republic of China School of Materials Science and Engineering Xi’an University of TechnologyXi’an710048People’s Republic of China

Creep aging(CA)is a promising forming technology for integral panels with complex ***,how to balance excellent corrosion resistance and strength is still a challenge for CA *** synchronously applying electrical pulse(300 Hz,15 A/mm^(2))in the middle of steady-state CA of Al-Zn-Mg-Cu alloy,the electrically assisted CA(ECA)is proposed to induce retrogression rapidly for realizing a three-step aging(retrogression and re-aging,RRA)in CA to tailor the needed properties *** is compared with conventional CA with one-step aging(peak aging,T6 or over aging,T7),two-step aging(over aging,T73)and RRA in hardness,intergranular corrosion and *** the ECA of pre-aging and re-aging for 20 h plus electropulsing for 10 min,the hardness is 10.5%,20.5%and 18.9%higher than those of CA with T6,T7 and T73 processes,respectively,while the corrosion resistance is higher than T6 process and lower than T7 and T73 *** the hardness and corrosion resistance are comparable to those of the CA with the RRA process,ECA takes one hour less due to the accelerated effect of the electropulsing and is not limited by the thick *** improved comprehensive performance of the ECA sample is due to both fine intragranular precipitatesη′and large discontinuous grain boundary precipitatesη.

关键词： Creep aging(CA) Electrical pulse Retrogression Corrosion Hardness Al-Zn-Mg-Cu alloy