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On the Blaschke Isoparametric Hypersurfaces in the Unit Sphere

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Acta Mathematica Sinica,English Series 2009年第4期25卷 657-678页

作者： Xing Xiao li feng yun ZHANG Department of Mathematics. He'nan Normal University Xinxiang 453007 P. R. China

Given an immersed submanifold x ： M^M → S^n in the unit sphere S^n without umbilics, a Blaschke eigenvalue of x is by definition an eigenvalue of the Blaschke tensor of x. x is called Blaschke isoparametric if its Mobius form vanishes identically and all of its Blaschke eigenvalues are constant. Then the classification of Blaschke isoparametric hypersurfaces is natural and interesting in the MSbius geometry of submanifolds. When n = 4, the corresponding classification theorem was given by the authors. In this paper, we are able to complete the corresponding classification for n = 5. In particular, we shall prove that all the Blaschke isoparametric hypersurfaces in S^5 with more than two distinct Blaschke eigenvalues are necessarily Mobius isoparametric.

关键词： Mobius form Blaschke eigenvalues Blaschke tensor Mobius metric Mobius second fundamental form

Deformation resistance of Fe-Mn-V-N alloy under different deformation processes

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Rare Metals 2017年第10期36卷 833-839页

作者： yun-li feng Jie li li-Qun Ai Bao-Mei Duan College of Metallurgy and Energy North China University of Science and Technology Tangshan 063009 China Key Laboratory of the Ministry of Education for Modem Metallurgy Technology Tangshan 063009 China

The deformation resistance of Fe-Mn-V-N alloy under different deformation conditions was investigated by hot compression method on thermal simulator. Effects of deformation degree, deformation temperature, and strain rate on deformation resistance were analyzed. The results show that when other conditions are constant, the deformation resistance increases with the increase in deformation degree and strain rate and decreases with the increase in deformation temperature. At the same time, the mathematical model of deformation resistance for Fe-Mn- V-N alloy was established by lstOpt software using the Levenberg-Marquardt optimization algorithm carried out on the fitting of regression coefficients, which has higher fitting precision.

关键词： Fe-Mn-V-N alloy Deformation process Deformation resistance Mathematical model

Microstructure transformation of X70 pipeline steel welding heat-affected zone

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Rare Metals 2014年第4期33卷 493-498页

作者： Hui li Jing-Long liang yun-li feng Dong-Xing Huo College of Metallurgy and Energy Hebei United University

The continuous cooling transformation curve of heat-affected zone （HAZ） of X70 pipeline steel was mea- sured by Gleeble-3500 thermal mechanical simulator, optical microscope （OM） and hardness analysis. The microstructure transformation rule at different cooling rates and solution behaviors of microalloy carbonitride during heating process of simulated specimens were investigated. When the cooling rate changes from 10 to 20 ℃.s-l, microstructures at HAZ are identified as granular bainite, lathy bainite, and quasi-polygonal ferrite. This micro- structure is featured with fine ferrite grains, martensite/ austenite islands dispersed, high-density dislocations, and fine carbonitride particles, resulting in improving the strength and toughness of HAZ. With the cooling rate increasing to above 40 ℃.s-1, the microstructure is pre- dominantly coarse lathy bainite with clear primary aus- tenite grain boundary. While the cooling rate decreases to below 1 ℃.s-1, a fairly small amount of pearlite can be observed at the boundaries. The strength and toughness of HAZ are deteriorated because of coarse grains among these microstructures. Most of microalloy carbonitrides in HAZ could be dissolved in the matrix during heating process. A few of TiN particles existing as residues in the matrix can prevent austenite grain from growing, and then improve the strength and toughness of HAZ.

关键词： X70 pipeline steel Heat-affected zone Microstructure transformation Acicular ferrite

Constitutive Model of Warm Deformation Behavior of Medium Carbon Steel

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Journal of Iron and Steel Research International 2016年第9期23卷 940-948页

作者： Hong-bin li yun-li feng Tao YAN En-lin YU National Engineering Research Center for Equipment and Technology of Cold Strip Rolling Yanshan University College of Metallurgy and Energy North China University of Science and Technology Equipment Manufacturing College Hebei University of Engineering

The compressive behaviors of medium carbon steel specimens were investigated over a wide range of tem- peratures and strain rates using a Gleeble-3500 thermo-simulation machine. The results show that the flow stress in- creased with strain at first, and then gradually decreased after reaching a peak value. The flow stress softening rate at a high strain rate was larger than that at a low strain rate. The effects of deformation heating and friction on flow stress were analyzed. A new friction correction method, wherein the effect of strain on frictional coefficient was con- sidered, was established here. The stresses revised by the new method deviated from the measured stresses with in- creasing strain. Meanwhile, the apparent frictional coefficient variation law with strain was obtained. The frictional coefficient increased as the strain increased and then slightly decreased after maintaining a constant value. The stress was corrected by considering deformation heating. The accuracy of the temperature correction method was verified using a special experiment. The results of the verification experiment show that the temperature correction method exhibited a good accuracy in calculating the variation of stress caused by deformation heating. A constitutive model considering strain was proposed here to describe the deformation behaviors. Compared with experimental data, the modified constitutive model exhibited a good accuracy as to constitutive correlation.

关键词： friction correction temperature correction deformation heating flow stress constitutive model

Dependence of tensile properties on microstructural features of bimodal-sized ferrite/cementite steels

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Journal of Iron and Steel Research International 2017年第1期24卷 67-76页

作者： Jiang-li Ning yun-li feng Ming-ming Wang Shen-bai Zheng Jie li College of Metallurgy and Energy North China University of Science and TechnologyTangshan 063009HebeiChina

A medium-carbon steel was processed through different warm rolling techniques,and the microstructural features with bimodal grain size distribution were found to be *** combination of strength and ductility was ameliorated in the steel processed through warm rolling characterized by biaxial *** enhanced strength is attributed to the densely distributed fine intragranular cementite particles and the small grain size in the coarse grain *** enhanced uniform elongation is due to the improved work hardening behavior at the large-strain *** work hardening behavior is predominantly ascribed to the finely dispersed intragranular *** relatively small grain size with nearly equiaxed shape in the coarse grain regions helps stabilize the uniform deformation to a large strain.

关键词： Tensile property Ferrite/cementite steel Bimodal-sized structure Warm rolling Work hardening rate

Balanced solubility product and enthalpies of formation of Nb compounds in 0.09 % oriented silicon steel

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Rare Metals 2013年第3期32卷 318-322页

作者： Hui li yun-li feng Dan Zhang Meng Song Da-Qiang Cang School of Metallurgical and Ecological Engineering University of Science and Technology Beijing School of Metallurgy and Energy Hebei United University

Balance solubility products and enthalpy of for- mation for NbC0.75, NbC0.85, NbC0.88, NbC and NbN in oriented silicon steels were calculated and compared quali- tatively. Meanwhile, the mixing enthalpies of these five Nb compounds were calculated based on Miedema Model. The results show that the solubility products of Nb compounds in ferrite and austenite meet the following relationship, NbC0.75 〉 NbC0.85 〉 NbC0.88 〉 NbC 〉 NbN and NbN has the minimum enthalpy of formation. It indicates that NbN easily precipitate out, but it is more difficult for NbC0.75.

关键词： Oriented silicon steel Nb compounds Solubility formula Enthalpy of formation

Tension-Compression Yield Asymmetry Influenced by the Variable Deformation Modes in Gradient Structure Mg Alloys

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Acta Metallurgica Sinica(English Letters) 2020年第2期33卷 252-266页

作者： Jiang-li Ning Bo Xu yun-li feng Xu-Dong li Xin-Kang li Wei-Ping Tong College of Metallurgy and Energy North China University of Science and TechnologyTangshan 063210China Key Laboratory of Electromagnetic Processing of Materials Ministry of EducationNortheastern UniversityShenyang 110004China

Surface mechanical attrition treatment(SMAT) was carried out on hot-rolled AZ31 Mg samples along two orthogonal directions;as a result,two types of gradient structures with different grain sizes and texture components in different layers were *** tension-compression yield asymmetry(YA) was studied using samples with different thicknesses,in order to elucidate the effect of combinations of variable deformation modes operating in different layers of the two oriented SMAT *** 0° oriented SMAT sample containing layers with strong basal texture displayed significant YA,because of either dislocation slip or extension twinning domination during tension or *** contrast,the 90° oriented SMAT sample containing layers with coexisting orthogonal texture components had an obviously weakened YA,which was attributed to the multi-deformation modes cooperating during tension or compression,i.e.,extension twinning or detwinning in conjunction with dislocation slips,leading to close yield stresses compared between tension and compression.

关键词： Mg alloy Gradient structure Yield asymmetry Texture Deformation mechanism

Nanoscratching and mechanical behaviors of high-entropy alloys with different phase constituents

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Journal of Iron and Steel Research International 2019年第11期26卷 1240-1248页

作者： Jiang-li Ning yun-li feng Xu-dong li Qi-bo Deng Yong-jiang Huang College of Metallurgy and Energy North China University of Science and TechnologyTangshan 063210HebeiChina Tianjin Key Laboratory of Advanced Functional Porous Materials Institute for New Energy Materials and Low-Carbon TechnologiesSchool of Materials Science and EngineeringTianjin University of TechnologyTianjin 300384China School of Materials Science and Engineering Harbin Institute of TechnologyHarbin 150001HeilongjiangChina

High-entropy alloys(HEAs)exhibit unique microstructural features and properties in nanoscale and atomic scale because of their multi-element alloy *** nanoscratching behaviors of three HEAs with different phase constituents,relative to the microstructure and mechanical properties of the HEAs,were *** typical phase constituents were selected:face-centered cubic(FCC)structure,body-centered cubic(BCC)structure,and a dual-phase structure containing both FCC and BCC *** the fact that the FCC alloy has the highest ductility and strain hardening capability,it exhibited inferior scratch resistance due to the over-softening of *** to the brittle failure mode,the BCC alloy hardly exhibited desirable scratch resistance despite its highest *** contrast,the nanostructured dual-phase alloy exhibited the best scratch resistance because of its good combination of strength and ductility,as well as the ductile failure *** research suggests that the HEA with structure comprising nanoscale hard and soft phases is desirable for nanoscratch resistance,and possesses appropriate hardness for industrial applications.

关键词： High-entropy alloy Nanoscratch Mechanical property Microstructure-Failure mode

Dynamics and control of a solar collector system for near Earth object deflection

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Research in Astronomy and Astrophysics 2011年第2期11卷 205-224页

作者： Shen-Ping Gong,Jun-feng li and yun-feng Gao School of Aerospace,Tsinghua University,Beijing 100084,China School of Aerospace Tsinghua University Beijing 100084 China

A solar collector system is a possible method using solar energy to deflect Earth-threatening near-Earth *** investigate the dynamics and control of a solar collector system including a main collector （MC） and secondary collector （SC）.The MC is used to collect the sunlight to its focal point,where the SC is placed and directs the collected light to an *** the relative position and attitude of the two collectors should be accurately controlled to achieve the desired optical ***,the dynamical equation of the relative motion of the two collectors in the vicinity of the asteroid is ***,the nonlinear sliding-mode method is employed to design a control law to achieve the desired configuration of the two ***,the deflection capability of this solar collector system is compared with those of the gravitational tractor and solar sail gravitational *** results show that the solar collector is much more efficient with respect to deflection capability.

关键词： minor planets asteroids -- techniques: miscellaneous -- solar collector