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Convergence Tips: PolyUMod with COMSOL

Getting Started

Note: We included a COMSOL model that has all the steps listed below. The model PolyUModCOMSOL_TNM_Demo1 is located in the PolyUMod folder:
C:\Program Files\PolymerFEM\PolyUMod\Test_Cases_COMSOL

  1. Right click on Global Definition > Materials and select External Material
  2. In the Library input locate the polyumod.dll file. By default this file should be the PolyUMod installation directory in sub-folder
    C:\Program Files\PolymerFEM\PolyUMod\PolyUMod_COMSOL_5.5. Provide the full path in the input box, not just the filename. The directory used here must be included in the PATH environment variable. See installation for details.
  3. Change the Interface type to Lagrangian Interface to PolyUMod. If this option is not available check that the .jar file specified in the installation is copied to the right place.
  4. Rename the State name to SS or any other variable not already used by COMSOL
  5. Define the Material model parameters array in the Material Contents section. The array has the PolyUMod material constants, comma separated and enclosed in {} brackets. This array can be input manually or exported from the MCalibration software.
  6. Input the Number of states according which is also output by the MCalibration software and depends on the selected material model
  7. In the Solid Mechanics physics select Material Models > External Stress-Strain Relation. Select the applicable domains and make sure the External material input points to the correct external material model.

Recommended Analysis Settings

  1. We recommend only using the PolyUMod materials with Time Dependent solvers. Inertia terms may be ignored by setting Structural Transient Behavior to Quasi-static.
  2. In the Time Dependent Solver node set Steps taken by solver to Strict. This requires COMSOL to solve exactly at the time steps required for output.
  3. Set the Maximum step to a reasonably small value that ensures the solver will not take big steps. This is important since most of the material models in PolyUMod are path dependent, and large steps compromise material model accuracy.
  4. Set Consistent initialization to Off. Manually check that the initial conditions are consistent.
  5. Both Segregated and Fully Coupled solvers can be used with PolyUMod. If you use a Fully Coupled solver set Maximum number of iterations to 10. Also use one of the following solver Newton iteration settings:
    1. Set Nonlinear method to Automatic (Newton)
    2. Set Nonlinear method to Constant (Newton) and set Jacobian update to On every iteration. This helps with convergence for highly nonlinear material models.

Error Checking

If a COMSOL with PolyUMod material does not converge then check the following:

  1. Check that a Time Dependent solver is selected
  2. Check that Steps taken by the time dependent solver is set to Strict
  3. Check that Consistent initialization in the time dependent solver is set to Off
  4. PolyUMod license is active. One way to check this is to run MCalibration.
  5. Check that the polyumod.dll file is in a directory defined in the PATH

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