Dear all,
I’m trying to model multilayer soil in abaqus. To use the SaniSand umat in model I use the following parameters but no plastic strain at all. The unit system used is us(in). Are the input parameters incorrect?
Could anyone kindly help me solve this problem? Thanks a lot!.


  1. Piotr Kowalczyk
    Piotr Kowalczyk 5 years ago

    Hey Yousef

    The parameters look generally ok. Rather close to the original calibration of Dafalias & Manzari for Toyoura Sand. If you are using US units check if your G0 parameter, which is indeed unitless, is still 125 or is it different value.

    Good luck


    • Yousef Zand Author
      Yousef Zand 5 years ago

      Thank you for replay
      G0 is a dimensionless constant, but by changing its value, PE is STEEL equal to zero.

      • Piotr Kowalczyk
        Piotr Kowalczyk 5 years ago

        Hey Yousef

        As mentioned by Arie, PE is not calculated by the umat. It is calculated only by the constitutive models implemented in Abaqus. If you want to see if plastic strains occur from the umat, then read umat carefully and try to ask for your own output in log file. I am not sure if you can ask for the actual value of the plastic strain.


  2. Arie Koot
    Arie Koot 5 years ago

    What do you mean “no plastic strain”?
    Sanisand umat does not calculate plastic strain: it is a kinematic hardening model with one backstress.
    It only needs and calculates plastic strain rate.

    • Yousef Zand Author
      Yousef Zand 5 years ago

      Thank you for replay

      PE in visualization always is zero
      though with chang in load and b.c
      is this correct؟

  3. Arie Koot
    Arie Koot 5 years ago

    Or do you mean you miss plastic strain input?
    Hardening behavior is described by the hardening parameters

  4. Yousef Zand Author
    Yousef Zand 5 years ago

    i set depvar=36
    and check pe in field output in step
    and select umat in job
    Something else needs to be done؟

  5. Arie Koot
    Arie Koot 5 years ago

    select pe has no use: it is not calculated by sanisand.
    You can select SDV output but then you get all 36 statevar. (you cannot select a few)
    It will make your odb larger but it gives you more information.

    c 1 … alpha_11 back stress, orientation of yield surface cone
    c 2 … alpha_22
    c 3 … alpha_33
    c 4 … alpha_12
    c 5 … alpha_13
    c 6 … alpha_23
    c 7 … void void ratio
    c 8 … Fab_11 fabric tensor z
    c 9 … Fab_22
    c 10 … Fab_33
    c 11 … Fab_12
    c 12 … Fab_13
    c 13 … Fab_23
    c 14 … not used
    c group 2: memory variables for shear reversal (SR) and other purposes
    c 15 … alpha_sr_11 alpha value at stress reversal points (discrete update)
    c 16 … alpha_sr_22
    c 17 … alpha_sr_33
    c 18 … alpha_sr_12
    c 19 … alpha_sr_13
    c 20 … alpha_sr_23
    c 21 … not used
    c 22 … not used
    c 23 … not used
    c 24 … not used
    c 25 … not used
    c 26 … not used
    c 27 … not used
    c 28 … not used
    c group 3: variables saved for post processing or other purposes
    c 29 … pore excess pore pressure (undrained case)
    c 30 … p mean effective stress
    c 31 … q deviator stress
    c 32 … z Lode parameter (cos(3theta))
    c 33 … dtsub suggested size of first time substep
    c 34 … nfev number of function evaluation
    c 35 … not used
    c 36 … not used

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