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Abstract：
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A modified kinematically admissible velocity field for the backward extrusion of internally circular shaped tubes from arbitrarily shaped billets is proposed. The original velocity fields appearing in the liberature did not satisfy the condition that the normal velocity on the die and material interface must be zero, and material rotation under the punch was neglected. Therefore, in this work the fomer is corrected and the latter is improved by a new velocity field. From the proposed velocity field, the upper bound extrusion load and average extruded height for regular polygonal shaped billets are determined with respect of the chosen parameters. The theorelical predictions of extrusion load are lower and closer to the experimental results than those in the previous literature. The average extruded height and the grid distortion of theory and experiment agree well when using the proposed velocity field.
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Funds：
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国家自然科学基金
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AuthorIntro：
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Reference：
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1吕丽萍．有限元法及其在锻压工程中的应用．西安∶西北工业大学出版社，1989．2AritzurB．MetalForming，ProcessesandAnalysis．Huntington，Newyork．1979．3AritzurB，BishopEDandHalunWC．Trans．ASMESer．B，94（1972）1079．4HalunWC，AritzurB，BishopED．Trans．ASMESer．B，95（1973）849．5NagpalV．Trans．ASMESer．B，99（1977）624．6YangDYandHanCH．Trans．ASMESer．B，106（1984）143．7朱伯芳．有限单元法原理与应用．北京∶水利电力出版社，1979．8BaeWBandYangDY．JMater，Proc，Tech．，36（1993）157．9BaeWBandYangDY．JMater．Proc．Tech，36（1993）175．10HimmelblanDM．AppliedNonlinearProgramming．McGrawHil，NewYork，1972∶45111kudoH．Int．J．Mech．Sic．，2（1960）102，3（1961）91．12BaeWBandYangDY．J．Mater，Proce．Tech，30（1992）13．13罗迎社．温度、变形速度对铝合金的应力—应变关系的影响．锻压技术．1996，21（3）∶32～3614彭炎荣．塑性成形中的切向加载及其功率计算．锻压技术．1996，21（3）．
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