Dyna result doesn't match Test result

  1. I try many time to model a simple tensile test for steel MAT_024 but the graph doesn't match from Dyna result and Test result.
    Process:
    1. Collect data Tensile strain and stress convert to True stress and strain use formula True stress: eng. stress*(1+eng. strain). True strain= ln(1+eng. strain) and then the true strain convert to plastic strain = true strain - (true stress / Young modulus) and plot the graph
    [​IMG]

    2. Use MAT_024 from dyna
    [​IMG]
    [​IMG]
    3. Then I extract nodout and sec force.
    [​IMG]
    LN1 is left node 1 (triangle on left)
    RN1 is right node (triangle on right)

    4. Eng stress= Force/Ao and eng. strain= delta Length / original length and plot the graph. (original area is 40, original length is 45mm)
    [​IMG]
    [​IMG]
    [​IMG]

    Then the both result was different, why? What the misstake? Anyone can help me solve this problem?
     
    Last edited: Jul 21, 2010
  2. jcsd
  3. In the first figure, when you define the stress x plastic strain for the material, the maximum inputed value is around 0.5GPa for a strain of 0.3, but when you show the lab test stress x strain graph in the last figure, the maximum stress is around 0.37GPa for the same strain.
     
  4. The 1st figure is a plastic strain vs true stress as a input, is it right?
    if true stress vs strain and lab test strain stress the max. stress is different right?
     
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