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An Extended Chaboche's Viscoplastic Law at Finite Strains: Theoretical and Numerical Aspects

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Journal of Materials Science & Technology 2005年第2期21卷 145-147页

作者： R.C.Lin W.Brocks Institute for Materials research gkss research centre Max-Planck-Street D-21502 Geesthacht GermanyInstitute for Materials Research GKSS Research Centre Max-Planck-Street D-21502 Geesthacht Germany

This paper presents a newly extended Chaboche’s viscoplastic law at finite strains, so that the classical Chaboche’s theories can be applied to the physical and numerical simulation of metals processing and behavior description of spatial metal structures. The extension is based on a new dissipation inequality at finite strains. The evolution equations are formulated in terms of the corotational rates of the logarithmic elastic strain and the strain-like internal variable conjugate to the back stress as well as the material time derivative of the accumulated plastic strain. The stress equation is expressed on the hyperelastic theory. Therefore, the possible inconsistency with elasticity, caused by the hypoelastic equations, is completely removed. A set of numerical examples with finite deformations are presented to prove the effectivities of the new model and numerical algorithms.

关键词： Viscoplastic law Dissipation inequality Finite strain

Recycling of magnesium drive train components

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Science China(Technological Sciences) 2009年第1期52卷 148-154页

作者： Daniel FECHNER Carsten BLAWERT Norbert HORT Karl Ulrich KAINER MagIC-Magnesium Innovation centre GKSS Research Centre Max-Planck-Straβe 1

With the development of new heat resistant magnesium alloys, the automotive industry has introduced several parts to the drive train. The rising number of large magnesium components will result in a higher quantity of automotive post consumer scrap. It was the aim of this work to find a reasonable alloy system for the recycling of these magnesium drive train components. A matrix of potential recy-cling alloys based on the magnesium alloy AM50 was prepared via permanent mould casting. The materials were investigated via tensile testing, creep tests and salt spray tests. Three alloys were selected for processing via high pressure die casting and the tests were repeated on the new materials. A promising system for recycling has been isolated and will be investigated more deeply for the influence of impurities.

关键词： magnesium recycling end-of-life vehicles recycling alloy post consumer scrap

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Acta Metallurgica Sinica(English Letters) 1995年第Z1期8卷 349-358页

作者： CHRISTOPH Ulrich, SPARKA Ulf APPEL Fritz, and WAGNER Richard(Institute for Materials research, gkss research Center, Max-Planck-Str. ,D-21502 Geesthacht, Germany) gkss research Center Geesthacht Germany

Deformation micromechanisms of two-phase titanium aluminide alloys have been investigated by deformation tests and electron microscope observations. Interaction mechanisms of perfect and twinning dislocations with the lamellar interfaces were characterized with respect to the factors governing the multiplication and the slip paths of the dislocations. Thermally activated processes controlling the dislocation mobility were described in terms of activation volumes and activation *** analysis is aimed at the identification of the dislocation processes operating under deformation conditions which are relevant for practical applications.

关键词： DEFORM PHAS

Effects of methyl-,phenyl-,ethylmercury and mercurychlorid on immune cells of harbor seals(Phoca vitulina)

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Journal of Environmental Sciences 2009年第12期21卷 1716-1721页

作者： Antje Kakuschke Elizabeth Valentine-Thon Sonja Fonfara Katharina Kramer Andreas Prange gkss research Center Institute for Coastal Research Department of Immunology Laboratory Center Bremen

Mercury （Hg） is present in the marine environment as a natural metal often enhanced through human activities. Depending on its chemical form, Hg can cause a wide range of immunotoxic effects. In this study, the influence of methyl-, ethyl- and phenylmercury as well as mercurychloride on immune functions was evaluated. Two parameters of cellular immunity, proliferation and mRNA cytokine expression of interleukin-2, -4, and transforming growth factor β, were investigated in harbor seal lymphocytes after in vitro exposure to Hg compounds. While all Hg compounds had a suppressive effect on proliferation, differences between juvenile and adult seals were found. Lymphocytes from juveniles showed a higher susceptibility to the toxic effect compared to lymphocytes from adults. Furthermore, the degree of inhibition of proliferation varied among the four Hg compounds. The organic compounds seem to be more immunotoxic than the inorganic compound. Finally, for the cytokine expression of methylmercury-incubated lymphocytes, timedependent changes were observed, but no dose-dependency was found. Marine mammals of the North Sea are burdened with Hg, and lymphocytes of harbor seals may be functionally impaired by this metal. The present in vitro study provides baseline information for future studies on the immunotoxic effects of Hg on cellular immunity of harbor seals.

关键词： harbor seal mercury lymphocyte proliferation cytokine expression North Sea

Atomistic simulation of tension deformation behavior in magnesium single crystal

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Acta Metallurgica Sinica(English Letters) 2010年第5期23卷 370-380页

作者： Yafang GUO Yuesheng WANG Honggang QI Dirk STEGLICH Institute of Engineering Mechanics Beijing Jiaotong University Beijing 100044 China gkss research centre Institute of Materials Research Materials Mechanics D-21502 Geesthacht Germany Graduate Institute of Ferrous Technology Pohang University of Science and Technology Pohang Gyeongbuk 790-784 Korea

The deformation behavior in magnesium single crystal under c-axis tension is investigated in a temperature range between 250 K and 570 K by molecular dynamics simulations. At a low temperature, twinning and shear bands are found to be the main deformation mechanisms. In particular, the {102} tension twins with the reorientation angle of about 90 °are observed in the simulations. The mechanisms of {102} twinning are illustrated by the simulated motion of atoms. Moreover, grain nucleation and growth are found to be accompanied with the {102} twinning. At temperatures above 450 K, the twin frequency decreases with increasing temperature. The {102} extension twin almost disappears at the temperature of 570 K. The non-basal slip plays an important role on the tensile deformation in magnesium single crystal at high temperatures.

关键词： Atomistic simulations Magnesium Twinning c-axis tension

Effect of the formation process of transient liquid phase (TLP) on the interface structure of TiAl joints

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Journal of University of Science and Technology Beijing 2005年第5期12卷 431-435页

作者： Huiping Duan Jun Luo Karl-Heinz Bohm Mustafa Kogak School of Materials Science and Technology Beijing University of Aeronautics and Astronautics Beijing 100083 China Institute for Materials research GKSS Research Center Geesthacht 21502 Germany

TiAl has been joined employing the transient liquid phase （TLP） bonding with Ti combined with Cu, Ni or Fe foils. Experimental results showed that though the interface structures of the joints are quite different, all the joined zones are composed of five sublayers, i.e. two diffusion zones, two interfacial zones and an interlayer. It has been convinced that the formation process of the transient liquid phase controls the diffusion behavior of melting point depressant （MPD） Cu, Ni, and Fe atoms, which leads to form different interface structures of the joints.

关键词： TiAl transient liquid phase (TLP) bonding interface

Effect of hot extrusion on microstructure and mechanical properties of quasicrystal-reinforced Mg-Zn-Yalloy

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中国有色金属学会会刊：英文版 2005年第4期15卷 715-721页

作者：郑明毅乔晓光徐世伟甘为民吴昆 S.Kamado Y.Kojima H.G.Brokmeier School of Materials Scienceand Engineering Harbin Institute of Technology Department of Mechanical Engineering Nagaoka University of Technology Institute of Materials Engineering GKSS-Research Center

The microstructure and mechanical properties of as-cast and as-extruded Mg-Zn-Y alloy （Mg-11%Zn-0.9%Y, mass fraction） containing Mg3YZn6 quasicrystal were studied. The eutectic icosahedral quasicrystal phase （I-phase） is broken and almost distributes along the extrusion direction, and fine I-phase with nano-size is precipitated during the extrusion. The α-Mg matrix grains are refined due to recrystallization occuring during the hot extrusion. Some {1012} twins are observed in the extruded ZW1101 alloy. And {0002}〈1010〉 fiber texture is formed in matrix alloys after hot extrusion. The extruded alloy exhibits high strength in combination with large elongation at room temperature. The strengthening mechanism of the as-extruded alloy was discussed.

关键词：镁合金微结构热突出锌

Electrochemical behavior of magnesium alloys in simulated body fluids

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中国有色金属学会会刊：英文版 2007年第A1期17卷 166-170页

作者：曾荣昌陈君 W.Dietzel N.Hort K.U.Kainer School of Materials Science and Engineering Chongqing Institute of Technology gkss research centre Geesthacht CmbH Geesthacht 21502Germany

Potentiodynamic electrochemical technique was utilized to study the corrosion behavior of magnesium alloys in simulated body fluids(SBFs). The influence of materials,solutions and their temperature on corrosion rate was mainly discussed. The results demonstrate that the free corrosion potential(Ecorr) of AZ31 and AZ91 alloys rises rapidly at initial stage,and then stabilizes at some value. Ecorr of WE43 alloy increases continuously. While Ecorr of AZ91 alloy with macro-arc oxidation(MAO) coating decreases drastically in 3 min,and then fluctuates between -1 607 mV and -1 503 mV. The WE43 alloy has better corrosion resistance in Hank's solution,compared with AZ31 and AZ91 alloys. Corrosion rates of the alloys are sensitive to the chemical composition and temperature of SBFs. A thin MgF2 film slightly improves corrosion resistance. An MAO coating on AZ91 alloy significantly reduces corrosion rate and enhances Ecorr. Pitting corrosion occurs on both AZ31 and WE43 alloys in Hank's solution.

关键词：镁合金生物材料腐蚀特性氧化技术

Interface evolution of TiAl/Ti6242 transient liquid phase joint using Ti, Cu foils as insert metals

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中国有色金属学会会刊：英文版 2005年第2期15卷 375-378页

作者：段辉平 K.H.Bohm V.Ventzke M.Koak School of Materials Science and Engineering Beijing University of Aeronautics and Astronautics Beijing 100083 China Institute for Materials research GKSS Research Center Geesthacht Geesthacht D-21502 Germany

The interface evolution of TiAl/Ti6242 joint produced by transient liquid phase(TLP) bonding with Ti, Cu foils as insert metals was investigated. The results show that the surface oxide layer on TiAl plays a very important role in the formation process of the joint. A ‘bridge’ effect is observed because of the presence of the oxide layer on the surface of TiAl. The diffusion behavior of Cu atoms in TiAl is strongly controlled by the vacancies beneath the surface of TiAl. Based on the interface diffusion and interface wettability, a mechanism for the effect of bonding pressure, bonding temperature, holding time and stacking sequence of the insert foils on the joint formation process were proposed.

关键词：铝钛合金瞬态液相压焊表面蒸气机械性能