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Journal of Materials Science & technology 2004年第5期20卷 561-566页

作者： RuihengWU XueyuRUAN HongbingZHANG t.y.Hsu DepartmentofPlasticitytechnology ShanghaiJiaoTongUniversityShanghai200030China Departmentof.MaterialsEngineering ShanghaiInstituteofTechnologyShanghai200233China SchoolofMaterialsScieuceaudEugineering ShanghaiJiaoTougUuiversityShanghai200030China

By combining the α/γ interface migration and the carbon diffusion at the interface in Fe-C alloys, a mathematical model is constructed to describe the mixed-control mechanism for proeutectoid ferrite formation from austenite. In this model, the α/γ interface is treated as non-equilibrium interface, i.e., the carbon concentration of austenite at γ/α interface is obtained through theoretical calculation, instead of that assumed as the local equilibrium concentration. For isothermal precipitation of ferrite in Fe-C alloys, the calculated results show that the rate of interface migration decreases monotonically during the whole process, while the rate of carbon diffusion from γ/α interface into austenite increases to a peak value and then decreases. the process of ferrite growth may be considered as composed of three stages: the period of rapid growth, slow growth and finishing stage. the results also show that the carbon concentration of austenite at γ/α interface could not reach the thermodynamic equilibrium value even at the last stage of ferrite growth.

关键词： Proeutectoid ferrite precipitation Non-equilibrium interface Phase transformation kinetics Mixed-control mechanism

Dynamic stiffness for thin-walled structures by power series

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2006年第8期7卷 1351-1357页

作者： ZHU Bin LEUNG A.y.t. Department of Civil Engineering Zhejiang University Hangzhou 310027 China Department of Building and Construction City University of Hong Kong Hong Kong China

the dynamic stiffness method is introduced to analyze thin-walled structures including thin-walled straight beams and spatial twisted helix beam. A dynamic stiffness matrix is formed by using frequency dependent shape functions which are exact solutions of the governing differential equations. With the obtained thin-walled beam dynamic stiffness matrices, the thin-walled frame dynamic stiffness matrix can also be formulated by satisfying the required displacements compatibility and forces equilib-rium, a method which is similar to the finite element method (FEM). then the thin-walled structure natural frequencies can be found by equating the determinant of the system dynamic stiffness matrix to zero. By this way, just one element and several elements can exactly predict many modes of a thin-walled beam and a spatial thin-walled frame, respectively. Several cases are studied and the results are compared with the existing solutions of other methods. the natural frequencies and buckling loads of these thin-walled structures are computed.

关键词： Dynamic stiffness method thin-wall structures Power series Buckling

CONStRUCtION OF QUANtUM FIELD tHEORy OF DISLOCAtIONS BASED ON tHE NON-RIEMANNIANPLAStICIty

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Acta Metallurgica Sinica(English Letters) 1998年第6期11卷 405-411页

作者： t.Hasebe y.Imaida Doshisha Univ Kyoto Japan

A new microscopic approach was proposed, which bridges the order gap between the dislocation theory and the crystalline plasticity based on the quantum field theory of dislocations. the Ginzburg-Landau equation was derived rigorously from the quantized Hamiltonian for a crystal body containing a large number of dislocations, which gives the reaction-diffusion (RD) type differential equations. the RD equation describes periodic patterning shown in PSBs, etc.. relationship between the proposed theory and the concepts appeared in the non-Riemannian plasticity was extensively discussed by introducing the gauge field of dislocations. (Edited author abstract) 15 Refs.

关键词： crystalline plasticity field theory Non-Riemannian plasticity,dislocation theory gauge field

Processing and Performance of Alumina Fiber Reinforced Alumina Composites

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Journal of Materials Science & technology 2003年第4期19卷 337-340页

作者： P.y.Leet t.Uchijima t.yano Research Laboratory for Nuclear Reactors Tokyo Institute of Technology2-12-1O-okayamaMeguro-kuTokyo152-8550JapanResearch Laboratory for Nuclear ReactorsTokyo Institute of Technology2-12-1O-okayamaMeguro-kuTokyo152-8550JapanResearch Laboratory for Nuclear ReactorsTokyo Institute of Technology2-12-1O-okayamaMeguro-kuTokyo152-8550Japan

Processing of alumina fiber-reinforced alumina matrix composites by hot-pressing was described. the mechanical properties of the composites fabricated by different sintering conditions including temperature and pressure have been investigated. the results indicated that the higher sintering temperature and pressure corresponded to the higher bulk density and higher maximum strength of the composite, whereas the pseudo-ductility of the composite was lower. the preliminary results of the composite with monazite-coated fibers showed that maximum strength could be improved up to 35% compared with the noncoated fiber composite in the same sintering condition. Moreover, the fracture behavior of the composite changed from completely brittle fracture to non-brittle fracture under the suitable sintering conditions. SEM observation of the fracture surface indicated that the coating worked as a protective barrier and avoided sintering of the fibers together even at high temperature and pressure during densification process.

关键词： Al2O3/Al2O3 composites Mechanical properties Hot-pressing Fiber reinforced composites

Effect of refinement of grains and icosahedral phase on hot compressive deformation and processing maps of Mg-Zn-y magnesium alloys with different volume fractions of icosahedral phase

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Journal of Materials Science & technology 2019年第1期35卷 181-191页

作者： t.y.Kwak W.J.Kim Department of Materials Science and Engineering Hongik University

the effect of the volume fraction of I-phase on the hot compressive behavior and processing maps of the extruded Mg-Zn-y alloys was examined, and the obtained results were compared with those of the cast alloys in a previous work. the average grain sizes, fractions of dynamically recrystallized(DRXed) grains,and sizes of DRXed grains of the extruded alloys after compressive deformation were significantly smaller,higher and smaller, respectively, than those of the cast alloys after compressive deformation under the same experimental conditions. this was because the microstructures of the extruded alloys, having much more grain boundaries and more refined I-phase particles than the cast alloys, provided a larger number of nucleation sites for dynamic recrystallization than those of the cast alloys. the constitutive equations for high-temperature deformation of the extruded and cast alloys could be derived using the same activation energy for plastic flow, which was close to the activation energy for lattice diffusion in *** with the cast alloys, the onset of the power law breakdown(PLB) occurred at larger ZenerHolloman(Z) parameter values in the extruded alloys. this was because the extruded alloys had finer initial grain sizes and higher fractions of finer DRXed grains compared to the cast alloys, such that the onset of PLB caused by creation of excessive concentrations of deformation-induced vacancies was delayed to a higher strain rate and a lower temperature. the flow-stress difference between the extruded alloys and the cast alloys could be attributed to the difference in the fraction of DRXed grains. According to the processing maps, the extruded alloys exhibited higher power dissipation efficiency and flow stability than the cast alloys. this agreed with the microstructural observations.

关键词： Hot compression Magnesium alloy Processing map Grain refinement Dynamic recrystallization

Superplastic behavior of an ultrafine-grained Mg-13Zn-1.55y alloy with a high volume fraction of icosahedral phases prepared by high-ratio differential speed rolling

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Journal of Materials Science & technology 2017年第9期33卷 919-925页

作者： t.y.Kwak W.J.Kim Rare Metal R&BD Group Korea Institute of Industrial Technology Department of Materials Science and Engineering Hongik University

An ultrafine-grained（UFG） Mg-13Zn-1.55 y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） on the cast microstructure following homogenization. the alloy exhibited excellent superplasticity at low temperatures(tensile elongations of 455% and 1021% 473 K-10;s;and 523 K-10;s;,respectively). Compared with UFG Mg-9.25Zn-1.66 y alloy（ZW92） with a lower volume fraction of I-phase particles（4.1%）, which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond523 K, leading to a loss of superplasticity. the high-temperature deformation behavior of the HRDSRprocessed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K.

关键词： Magnesium alloy Superplastic deformation Ultrafine grain Icosahedral quasicrystal Grain growth

A new design of dual-constituent triangular lattice metamaterial with unbounded thermal expansion

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Acta Mechanica Sinica 2019年第3期35卷 507-517页

作者： y.C.Zhang y.J.Liang S.t.Liu y.D.Su State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of TechnologyDalian 116024China New Functional Structural Design and Verification Key Laboratory of Aeronautical technology Shenyang 110035China

triangular lattice metamaterials composed of bi-layer curved rib elements (called the Lehman-Lakes lattice) possess unbounded thermal expansion, high stiffness and impossibility of thermal buckling, which are highly desirable in many engineering structural applications subjected to large fluctuations in temperature. However, the requirement of such lattice metamaterial is that it must be a hinged joint in order to achieve the bending deformation upon heating freely, which directly leads to poor manufacturability, especially in small dimensions. In this study, a new design of dual-constituent triangular lattice metamaterial (DtLM) with good manufacturability is proposed to achieve the identical unbounded thermal expansion. In this lattice, a special bi-layer curved rib element where layer one is partially covered by layer two is presented, where the hinge joints are not necessary because the flexural rigidity in the single-layer part is much smaller than that in the bi-layer part, and the desirable thermal bending deformation can be achieved. A sample fabricated by additive manufacturing is given in order to show the good manufacturability;simultaneously, the multifunctional performance of the tailored DtLM with zero, large positive or negative coefficient of thermal expansion (CtE) can remain excellent, as well as the Lehman-Lakes lattice. Examples illustrate that the DtLM with zero CtE has about 34.2% improvement in stiffness and meanwhile has 17% reduction in weight compared with the Lehman-Lakes lattice. the stiffness of the DtLM has a moderate reduction when achieving the same large positive or negative CtE. In addition, the thermomechanical properties of the DtLM are given by the closed-form analytical solution and their effectiveness is verified by the detailed numerical simulation.

关键词： Metamaterial Zero thermal expansion Lattice material Multifunctional design Additive manufacturing

Imaging global auroras in space

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Light(Science & Applications) 2019年第1期8卷 452-453页

作者： A.t.y.Lui JHU/APL LaurelMD 20723-6099USA

China’s initial participation in the global monitoring of auroras for scientific and space weather investigations has been enabled by the successful launch of the Chinese Fengyun-3D satellite,which carries a wide-fie... 详细信息

关键词： weather global space

Characterization for Fusion Candidate Vanadium Alloys

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Plasma Science and technology 2004年第4期6卷 2395-2399页

作者： t.Muroga t.Nagasaka J.M.Chen Z.y.Xu Q.y.Huang y.C.Wu NationalInstituteforFusionScience Toki509-5292Japan SouthwesternInstituteofPhysics Chengdu610041China InstituteofPlasmaPhysics ChineseAcademyofSciencesHefei230031China

this paper summarizes recent achievements in the characterization ofcandidate vanadium alloys obtained for fusion in the framework of the Japan-China Core UniversityProgram. National Institute for Fusion Science (NIFS) has a program of fabricating high-purityV-4Cr-4ti alloys. the resulting products (NIFS-HEAt-1,2), were characterized by various researchgroups in the world including Chinese partners. South Western Institute of Physics (SWIP) fabricateda new V-4Cr-4ti alloy (SWIP-Heat), and carried out a comparative evaluation of hydrogenembrittlement of NIFS-HEAts and SWIP-Heat. the tensile test of hydrogen-doped alloys showed that theNIFS-HEAt maintained the ductility to relatively high hydrogen levels. the comparison of the datawith those of previous studies suggested that the reduced oxygen level in the NIFS-HEAts should beresponsible for the increased resistance to hydrogen embrittlement. Based on the chemical analysisdata of NIFS-HEAts and SWIP-Heats, neutron-induced activation was analyzed in Institute of PlasmaPhysics (IPP-CAS) as a function of cooling time after the use in the fusion first wall. the resultsshowed that the low level of Co dominates the activity up to 50 years followed by a domination of Nbor Nb and Al in the respective alloys. It was suggested that reduction of Co and Nb, both of whichare thought to have been introduced via cross-contamination into the alloys from the molds usedshould be crucial for reducing further the activation.

关键词： vanadium alloys characterization nuclear fusion

Effect of Duct Geometry on Shock Wave Discharge

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Journal of thermal Science 2006年第4期15卷 349-354页

作者： y.-H.Kweon y.Miyazato t.Aoki H.-D.Kim t.Setoguchi Department of Energy and Environmental Engineering Kyushu UniversityKasuga 816-8580Japan Faculty of Environmental Engineering The University of KitakyushuKitakyushu 808-0135Japan School of Mechanical Engineering Andong National UniversityAndong 760-749Korea Department of Mechanical System Engineering Saga UniversitySaga 840-8502Japan

this paper describes computational work to understand the unsteady flow-field of a shock wave discharging from an exit of a duct and impinging upon a flat plate. A flat plate is located downstream, and normal to the axis of the duct. the distance between the exit of the duct and flat plate is changed. In the present study, two different duct geometries （i.e., square and cross section） are simulated to investigate the effect of duct geometry on the un-steady flows of a shock wave. In computation, the total variation diminishing （tVD） scheme is employed to solve three-dimensional, unsteady, compressible, Euler equations. Computations are performed over the range of shock Mach number from 1.05 to 1.75. Computational results can predict the three-dimensional dynamic behaviour of the shock wave impinging upon the flat plate. the results obtained show that the pressure increase generated on the plate by the shock impingement depends on the duct geometry and the distance between the duct exit and plate, as well as the shock Mach number. It is also found that for the duct with cross-section, the unsteady loads acting on the flat plate are less, compared with the square duct.

关键词： unsteady flow compressible flow shock wave shock impingement duct geometry