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Analysis in Theory and Applications 1999年第3期15卷 100-102页

作者： K.C.Chang q.y.shi D.G.Deng PekingUniversity PekingUniversityZhongshanUniversity

One-dimensional non-Darcy flow in a semi-infinite porous media:a multiphase implicit Stefan problem with phases divided by hydraulic gradients

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Acta Mechanica Sinica 2017年第5期33卷 855-867页

作者： G.q.Zhou y.Zhou X.y.shi State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and Technology School of Mechanics and Civil Engineering China University of Mining and Technology JiangSu Collaborative Innovation Center for Building Energy Saving and Construct Technology

One-dimensional non-Darcy flow in a semi-infinite porous media is investigated. We indicate that the non-Darcy relation which is usually determined from experimental results can always be described by a piecewise linear function, and the problem can be equivalently transformed to a multiphase implicit Stefan problem. The novel feature of this Stefan problem is that the phases of the porous media are divided by hydraulic gradients, not the excess pore water pressures. Using the similarity transformation technique, an exact solution for the situation that the external load increases in proportion to the square root of time is developed. The study on the existence and uniqueness of the solution leads to the requirement of a group of inequalities. A similar Stefan problem considering constant surface seepage velocity is also investigated, and the solution, which we indicate to be uniquely existent under all conditions, is established. Meanwhile, the relation between our Stefan problem and the traditional multiphase Stefan problem is demonstrated. In the end, computational examples of the solution are presented and discussed. The solution provides a useful benchmark for verifying the accuracy of general approximate algorithms of Stefan problems, and it is also attractive in the context of inverse problem analysis.

关键词： Moving boundary problem Stefan problem Analytical solution Non-Darcy flow Soil consolidation

Crack Initiation Mechanism of Z3CN20.09M Duplex Stainless Steel during Corrosion Fatigue in Water and Air at 290 °C

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Journal of Materials Science & Technology 2015年第11期31卷 1144-1150页

作者： H.C.Wu B.yang y.Z.shi q.Gao y.q.Wang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Collaborative Innovation Center of Universal Iron & Steel Technology School of Materials Science and Engineering Anhui University of Technology

The crack initiation mechanism of a Z3CN20.09M duplex stainless steel （DSS） during corrosion fatigue （CF） in water and air at 290 ℃ was investigated by using a CF cracking machine and a scanning electron microscopy （SEM）. The cracks were initiated successively at the persistent stip bands （PSBs）, phase boundaries （PBs） and pitting corrosion points （PCPs） of the specimens when they were tested in water at 290 ℃, while in airat 290 ℃ the cracks were only initiated at the PSBs and PBs. And the cracks were found mainly to initiate at the PSBs and PBs when the specimens were tested in water and air at 290 ℃, respectively. The results also reveal that the cracks were likely to be initiated at the first 20% of fatigue life of the specimens tested in water at 290 ℃. However, the cracks were not found until 50% of fatigue life when tested in air at 290 ℃. Moreover, the crack numbers of the specimens tested in water at 290 ℃ were much more than those tested in air at 290 ℃.

关键词： Duplex stainless steel Corrosion fatigue Crack initiation High temperature water

Tuning the microstructure for superb corrosion resistance in eutectic high entropy alloy

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Journal of Materials Science & Technology 2022年第14期109卷 197-208页

作者： S.Shuang q.yua X.Gao q.F.He J.y.Zhang S.q.shi y.yang Department of Mechanical Engineering City University of Hong KongKowloon TongKowloonHong KongChina Department of Mechanical Engineering Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina Department of Materials Science and Engineering City University of Hong KongKowloon TongKowloonHong KongChina

In this work,we demonstrate that the corrosion resistance of the FeCrNiCoNb_(0.5) eutectic high entropy alloy(EHEA)can be tuned by controlling the size of its eutectic *** microstructure refinement,the EHEA exhibits a superb corrosion resistance in 1 M NaCl in terms of a very low corrosion current density and an ultra-high transpassviation potential,which outperforms a variety of other HEAs and conventional metals and *** the fundamental level,the microstructure refinement results in a rapid formation of a thick and compact passive film with less Cl-adsorption on the EHEA,which results in significant enhancement in its corrosion *** outcome of our research provides important insights into the design of corrosion resistant chemically complex alloys.

关键词： Eutectic high entropy alloy Passivation Transpassivation potential Microstructure size

Reduction effect of final-pass heavy reduction rolling on the texture development,tensile property and stretch formability of ZWK100 alloy plates

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Journal of Materials Science & Technology 2022年第16期111卷 211-223页

作者： B.q.shi L.y.Zhao X.L.Shang B.H.Nie D.C.Chen C.q.Li y.q.Cheng School of Materials Science and Hydrogen Energy Foshan UniversityFoshan 528000China School of Materials and Energy Guangdong University of TechnologyGuangzhouGuangdong 510006China GD Midea Air-Conditioning Equipment Co. Ltd.Foshan 528311China Guangdong Key Laboratory of Hydrogen Energy Technology Foshan 528000China yunFu(Foshan)R&D Center of Hydrogen Energy Standardization Yunfu 527326China

Obviously planar anisotropy due to‘TD split’orthotropic texture(TD indicates Transverse direction)always exist in the Rare-earth(RE)or Ca containing Mg alloy sheets,which is likely caused by the lowreduction rolling(and annealing)as revealed in our previous *** this work,the as-cast billets of a ZWK100 alloy were subjected to final-pass heavy reduction rolling(FHRR)at 500°C with different reductions(30%-70%)after rough rolling,aiming to investigate the reduction effect on the microstructure and texture *** results show that FHRR with higher reductions above 50%is in favor of shear banding formation but has little effect on the as-deformed texture components,and the excellent formability with single-pass reduction up to 70%is mainly ascribed to the activation of prismatic *** with reduction above 50%and annealing can generate uniform grain structures of~10μm and symmetrical‘oblique-line split’texture in(0001)pole figures,with basal poles tilting by about 50°from ND(Normal direction)towards some oblique-line of TD and RD(Rolling direction)as well as uniform distribution of counter lines as an annular shape,resulting in excellent elongation to failure of~50%and ultra-low planar anisotropyΔr_of~0.1 and high stretch formability(Erichsen value:8.1).The formation‘oblique-line split’texture in(0001)pole figures is mainly correlated with the preferred growth tendency of grains with■//RD,which was suggested to relate to the high mobility of some special boundaries such as 40°-45°■.The influences of starting textures on the mechanical properties,planar anisotropy and related deformation modes,as well as their correlations with the stretch formability were comparatively investigated with the‘TD split’orthotropic texture as a counterpoint.

关键词： Magnesium alloys Texture Plane anisotropy Stretch formability Rolled sheets

A STUDy OF RATE-DEPENDENCE AT ELEVATED TEMPERATURE FOR AN Al-Cu-Mg ALLOy

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Acta Metallurgica Sinica(English Letters) 2004年第4期17卷 618-624页

作者： y.q.Wu H.J.shi K.S.Zhang Key Laboratory of Failure Mechanics Department of Engineering Mechanics Tsinghua UniversityBeijing 100084 China Department of Engineering Mechanics North-Western Polytechnical University Xi'an 710072 ChinaKey Laboratory of Failure Mechanics Department of Engineering Mechanics Tsinghua UniversityBeijing 100084 ChinaDepartment of Engineering Mechanics North-Western Polytechnical University Xi'an 710072 China

The hot deformation of an Al-Cu-Mg alloy was studied in the two temperature ranges (room temperature-300℃ and 400℃-480℃). The rate-independent flow curves are typical of elasto-plastic response with significant work hardening followed by strain softening below 300℃. Similar dislocation structures with high density tangled into grain interiors were observed by TEM, which suggests that the process of obstacles arresting mobile dislocations results in this macroscopically rate-independence. At 400-480℃, all rate dependent flow behaviors characterized by a continuous softening after an initial work hardening at a small plastic strain show large tensile elongations. Long dislocation segments around the second phases infer their good mobility to climb across obstacles. Grain boundary morphology observed by TEM suggests that the capacity of the grain boundaries to absorb the dislocations sensitively accounts for the rate-dependent mechanical properties.

关键词： rate dependence elevated temperature dislocations,grain boundary

SCALING PROPERTIES OF INTERFACES IN CRySTALS UNDER NONEqUILIBRIUM CONDITIONS

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Acta Metallurgica Sinica(English Letters) 1997年第5期10卷 415-418页

作者： shi, D.W. Huang, J.y. Long, q.W. Inst of Metal Research Chinese Acad of Sciences Shenyang China

An equation of Langevin type was proposed to describe the interface evolution in crystals under nonequilibrium conditions (such as in Cu-Fe or Cu-Co system upon ball milling). The scaling properties (H) of this equation is in good agreement with the Monte Carlo simulations described by Bellon and Averback. In this equation the volume diffusion and interface diffusion are all important and this is consistent with some experimental results.

关键词： Ball milling Binary alloys Crystals Mathematical models Nanostructured materials Surface roughness

STUDy ON DyNAMIC J-INTEGRAL OF MECHANICAL HETEROGENEOUS WELDED JOINT

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Acta Metallurgica Sinica(English Letters) 2004年第6期17卷 934-939页

作者： F.q.Tian D.y.He X.y.Li y.W.shi D.Zhang InstituteofCompositeMaterials ShanghaiJiaotongUniversityShanghai200030China SchoolofMaterialsScienceandEngineering BeijingPolytechnicUniversityBeijing100022China

Welded joint is a mechanical heterogeneous body, and mechanical heterogeneity has great effect on dynamic fracture behaviour of welded joints. In the present investigation, dynamic response curve and dynamic J-integral of practical undermatched welded joint and whole base and whole weld three-point-bend (TPB) models containing longitudinal crack are com- puted. Dynamic J-integral is evaluated using virtual crack extension (VCE) method and the computation is performed using MARC finite element code. Because of the effect of inertia, dynamic load response curve of computed model waves periodically. Dynamic J-integral evaluated by VCE method is path independent. The effect of inertia has little influence on dynamic J-integral curve. The value of dynamic J-integral of undermatched welded joint is lower than that of whole base metal and higher than that of whole weld metal. The results establish the foundation of safety evaluation for dynamic loaded welded structures.

关键词： virtual crack extension welded joint dynamic response curve dynamic J-integral

STUDy ON TEMPERATURE FIELD INDUCED IN HIGH FREqUENCy INDUCTION HEATING

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Acta Metallurgica Sinica(English Letters) 2006年第3期19卷 190-196页

作者： H. Shen Z.q. yao y.J. shi J. Hu School of Mechanical Engineering Shanghai Jiaotong University Shanghai 200030 China

A mathematical model was established for the temperature field developed during high frequency induction heating （HFIH） by Maxwell＇s equations. It required solving the coupled equations of the electromagnetic and temperature fields. The numerical simudation was performed using FEMLAB. The comparison of the calculations using the proposed model with experimental results showed a very good correlation. The effects of the heating parameters in high frequency induction such as the distance between the plate and the coil, the applied current, the frequency, and the turns of the coil on the temperature profiles developed in the plate were also discussed using the established model.

关键词： high frequency induction temperature field numerical simudation

NUMERICAL INVESTIGATION OF STRAIGHT-LINE LASER FORMING UNDER THE TEMPERATURE GRADIENT MECHANISM

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Acta Metallurgica Sinica(English Letters) 2006年第2期19卷 144-150页

作者： y.J. shi H. Shen Z.q. yao J. Hu School of Mechanical and Power Engineering Shanghai Jiaotong University Shanghai 200030 China

Laser forraing is a new flexible and dieless forming technique. To achieve the high accuracy forming, the temperature gradient mechanism （TGM） is studied. In the analysis of TGM, the plate bends about x-axis and about y-axis as well. To understand the deformation trend, the numerical simulation of deformation of plate is conducted by choosing different laser powers, laser spot diameters, scanning speeds, lengths, widths and thicknesses. From the results of simulation, it can be seen that the laser spot diameter, the scanning speed, laser power and thickness of plate play dominant roles in the laser forming process. However, the bending angles αx and αy show different trends with the variation of parameters. In addition, in comparison with above four parameters, the effect of length and width of plate on the beading angle may be neglected, but their effects are significant for the bending radius R.

关键词： laser forming temperature gradient mechanism metal plate