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Recent content by vumat721

  1. vumat721

    hollow cylinder torsion modelling in ABAQUS by rotational displacement

    oh, remove the cload on degree of freedom 5, maybe that will help.
  2. vumat721

    Plastic Strain Data for Steel and PTFE

    If your units are Pascals, then it is probably correct. You should be careful about blinding using material data...
  3. vumat721

    hollow cylinder torsion modelling in ABAQUS by rotational displacement

    Not sure.... You shouldn't have to change the BC's and Constraints when switching from Rotation to Moment control. How are you applying the moment? You should apply it to DOF 6 (which is rotation about axis 3). In the input file, it should look like: *Cload <node set>,6,<magnitude>
  4. vumat721

    Clarification on RHS of UEL

    I believe Abaqus accounts for any forces that you apply externally, so RHS is the negative of internal forces and you don't have to worry about adding/subtracting the external forces. Did this not work for you? Or are you just seeking information first?
  5. vumat721

    hollow cylinder torsion modelling in ABAQUS by rotational displacement

    The first thing I noticed in your file is that you are applying your rotation to axis 2 (UR2), but the cylinder is oriented along axis 3, so you should use UR3 to apply your rotation. Also, you should apply a zero displacement boundary condition to your reference node in all the other DOFs...
  6. vumat721

    First attempt at material nonlinearity, problem with plastic region

    What are the strains in your simulations? You only define material data up to a strain of (0.001 + 0.0018 = 0.0028) which is a pretty tiny strain. Does the experimental data continue to harden past this point? Or does it flatten out? If it continues to harden, they I'd recommend adding some more...
  7. vumat721

    mooney-rivlin material data

    As a baseline, you just need uniaxial stress strain data, just like for any other material model. I believe the Abaqus docs outline other possible tests (biaxial, triaxial, shear, etc) as well.
  8. vumat721

    hollow cylinder torsion modelling in ABAQUS by rotational displacement

    Create an analytical rigid part with a reference point. Then create a surface on the part. Put the part into your assembly and tie that surface to a matching surface on the deformable cylinder. (Sorry, can't open tars on this computer)
  9. vumat721

    abaqus warning !

    It depends on how many elements you have in your simulation and whether or not those three elements are in a critical region of your model. If you have 30,000 elements and only three are distorting, then you're probably okay. BUT, if those elements are near a critical region, then this could be...
  10. vumat721

    mooney-rivlin material data

    Mooney-Rivlin is a hyperelastic material model. Experimental data is not based on it, but rather may be fit by a mooney-rivlin model. Also, I'm not a bioengineer, but I doubt that mooney-rivlin is what you want to model bone.
  11. vumat721

    Hyperelasticity + Viscoelasticity

    Abaqus won't evaluate the viscoelastic part of the model when you use the CAE Evaluate button. It ignores it and just evaluates the hyperelastic portion. It looks like your creep time constant is really really small, which is why you see the initial spike and then the flattening out. Try to...
  12. vumat721

    Hyperelasticity + Viscoelasticity

    Have you tried your model with only the hyperelastic portion of the material model in a static step? If not, you can use CAE's "evaluate" function to test that the hyperelastic constants work properly. Also, I would start with a one element model and pull it in tension or compression at a...
  13. vumat721

    abaqus warning !

    But as corus hinted at... If the nodes at the tie interface look like they have moved too much, then you need to pay attention to the warning message.
  14. vumat721

    Error when calculating a hyperelastic model

    First make sure your material model is okay. For a hyperelastic model, you can use the "Evaluate" function in CAE. If that runs, then your material model is probably okay and you can move on to further debugging.
  15. vumat721

    abaqus warning !

    There's nothing wrong with that error message. All it's telling you is that it adjusted a lot of nodes to make sure they were in contact, but it didn't print them all to your data file. It's no big deal.
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