LS Dyna

LS Dyna

When to use Johnson Cook: MAT_015 and MAT_107

    • ssagar
      Subscriber

      Hi,

      I am performing an impact analysis using Johnson-Cook parameters. Saw there are 2 material models in LS-PREPOST. One is just plain Johnson-Cook and the other is Modified Johnson-Cook. I do not have the modification factors for the MAT_107 but this model allows me to place an initial temperature T0. Also, MAT_107 does not need an EOS. However, the facture is not looking accurate.

      Also, what is the purpose of the initial temperature, T0, because the J-C constitutive equation has T and not T0.

      In the forum, I already asked if J-C parameters would change if the reference temperature changes. There are some decrease in impact energy with temperature when T0 is increased. But not sure how it works. My specimen are impacted at various temperatures ( which I specify asT0 in my input card). Is the latter procedure accurate?

      Thank you very much,

      SS

    • Ram Gopisetti
      Ansys Employee
      what is your application concern, MAT_107 is for adiabatic heating not for temperature dependency material modelling , check MAT_015 for thermal dependency.
      Cheers, Ram
    • Ozen
      Subscriber
      Not sure if this helps you, but I read a study on the behavior of tungsten carbide from 2010, they used a Modified JC to get mostly-accurate simulation of the tungsten carbide projectile. The plain JC model gave incorrect data. The determination was for materials that behave like tungsten carbide, behaving both like a ductile and brittle material, the Modified JC model was more accurate. While the plain JC model was for ductile materials. Not sure if this helps, but thought I'd comment just in case.
    • ssagar
      Subscriber
      Thank you both,
      @Ozen: Only issue with MAT_107 is that I dont have the modified JC parameters. I just have A, B, n, C and m. I guess that may not be sufficient?
      @Ram: Application concern is that I have different initial temperatures for the Charpy impact specimens. Can the T0 be used in Card MAT_107 to adjust the initial temperature of the specimen? Or will each of the J-C parameters would be different for each initial temperature.
      Thanks
    • Ozen
      Subscriber
      Modified JC appears to have C and D4 removed. Here is the title of the study, you can find the PDF online free somewhere since it was government research: "Development of material models for semi-brittle materials like tungsten carbide" by John F. Moxnes, et al. Section 7.2 talks about how their modified JC is set up. By the looks of it, you do need the damage constants D1, D2, D3, D4*, and D5 (D4 and C are removed in this model). Outside of that, that's all I know, I never have tried to setup a model using that yet.
    • ssagar
      Subscriber
      @Ozen: Thank you very much for sending the reference study. Appreciate it, Will have a try.

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