General Mechanical

General Mechanical

Inserting plastic strain of a material

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    • dariomnava
      Subscriber

      Hi,

      I have tried to get the stress strain curve of a steel SA516 according to ASME BPVC VIII div 2.

      My material has a yield strength of fy=260 MPa at room temperature (20 ºC).

      As far as I know ansys needs to know plastic stress when plastic strain =0. In the following picture I have plotted true stress vs plastic strain (colum K vs colum A of the Excel). However, when placing the zero plasticity at yield strength (for fy=260MPa; ep=0), it is like my curve mismatches, (circled in blue). It is not unirform at that point.

    • jonsoln
      Subscriber
      Hi!
      At yield stress you already have 0,2% plastic strain (definition of yield strength). Using this as zero plastic strain will give you a discontinuous stress-strain curve. It is not very clear in earlier versions of the BPVC, but in the newest version I think it is explicitly stated that you should use a cutoff value for plastic strain of 2e-5 (if i remember correctly). Hence the first point in your plasticity model should be 130MPa with 0 plastic strain.
    • dariomnava
      Subscriber
      Hi
      Using the value of 130MPa with 0 plastic strain makes the plot look better, but now ansys will stablish the yield strenght of material at 130 Mpa instead of 260 won't it? I am a little bit lost...
      I was using ASME 2015


    • jonsoln
      Subscriber
      Yes, Ansys will start computing plastic strain when the stress reaches 130MPa, but this is indeed closer to reality than assuming zero plastic strain until 260MPa. You will still get the same stress-strain curve above 260MPa. There are no requirements in the elastic-plastic methods of BPVC of having zero plastic strain, so it doesn't matter if you have some plastic strain at low stress levels.
    • dariomnava
      Subscriber
      All right. I will start my plasticity curve at fy=130.

      Thank you so much jonsoln, I really appreciate your help

      Kind regards
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