Goals of this Tutorial
- Demonstrate how to use a PolyUMod® with Altair Radioss™ explicit FE solver.
- Information about how to select and calibrate a PolyUMod material model is presented in our “MCalibration® for Altair” tutorial.
- These documents are available on our from the following link: https://PolymerFEM.com/Altair
PolyUMod Library
- The PolyUMod library is a library of advanced (and accurate) user-material models for finite element modeling of polymers, biomaterials, and other non-linear materials.
- The PolyUMod library also contains a material database of already calibrated viscoplastic material models for common polymers (e.g. ABS, HDPE, PTFE, PC, EPDM, Silicone rubber).
- With the PolyUMod library engineers can perform very accurate Radioss FE simulations without becoming an expert in material model software development. All of the difficult development work has already been done!
What is a Material Model?
- Any product (such as a tire) will deform when exposed to a load. The amount of deformation depends on the stiffness of the material.
- A material model is an equation that relates the applied force (or stress) with the resulting deformation (or strain).
- Radioss contains many material models, such linear elastic, elastic-plastic, etc.
- The PolyUMod library contains additional material models for materials that exhibit non-linear time- or strain-dependence (like most polymers).
Another name for a material model is a “constitutive model”.
What are Material Parameters?
- A material model specifies the equations that convert between stress and strain for a material. An example of a material model is Linear Elasticity.
- The material parameters are the numbers that specify the properties of a specific material.
- Example: At small deformations, both steel and rubber can be approximately linear in their stress-strain response. That is, both can be represented using a Linear Elastic material model, but they have very different material parameters (such as stiffness).
Key PolyUMod Material Models
The Bergstrom-Boyce model is an excellent model for predicting the non-linear viscoelastic response of rubbers. Radioss already supports this model for brick elements. The PolyUMod library supports both brick elements and shell elements.
The Three Network (TN) model was developed for predicting the large-strain, viscoplastic response of thermoplastics (in a glassy state). The TN-model is an excellent generic model for predicting the response of many different classes of both amorphous and semicrystalline thermoplastics.
The Three Network Viscoplastic (TNV) model is a general purpose viscoplastic material model capable of capturing the experimentally observed behaviors of rubbers, thermoplastic elastomers, TPU, foams, and stiff plastics. The model can capture time-dependence, pressure-dependence of plastic flow, pressure-dependent volumetric response, damage accumulation, and triaxiality-dependent failure.
Brick Elements ( Example Test Problem )
Exemplar Problem
- A short cylinder of a thermoplastic material is held fixed at the bottom and sheared sideways at the top.
- The goal of the analysis is to determine the stress in the cylinder as the cylinder is being deformed.
- The files used for this example are located here:
C:\Program Files\PolymerFEM\PolyUMod_Altair\
TestCases_Radioss\TestCase_Cylinder_Shear_225E
_PolyUMod_TN_3D
Use the MCalibration software to calibrate the Three Network (TN) model to experimental data for the plastic material. The MCalibration software is discussed in more detailed in a separate tutorial.
From within MCalibration, export the calibrated material model parameters to a Radioss txt-file.
This is the contents of the exported material model. The material model is of the type: /MAT/USER01. The first 16 parameters are “control parameters” that specify certain behaviors of the material model. The remaining parameters are the material parameters.
The control parameters are discussed in detail in the PolyUMod User’s Manual
(“C:\Program Files\PolymerFEM\PolyUMod_Altair\Documentation\PolyUMod_Manual.pdf”)
The following are the key control parameters that are used by Radioss:
- ORIENT: Should be set to 0, 1, or 2 depending on the Isolid value defined by /PROP/SOLID.
- NPROP: Total number of control and material parameters.
- NHIST: Number of state variables that is used by the material model.
- GMU: Effective shear modulus. Is used to calculate the wave speed in the material.
- GKAPPA: Effective bulk modulus. Is used to calculate the wave speed in the material.
The ORIENT parameter controls how PolyUMod interprets the deformation gradient F that it receives from Radioss. If ORIENT=0, then PolyUMod assumes that F is in a global coordinate system. If ORIENT=1, then it uses the rotated RT F R. If ORIENT=2, then it uses the rotated R F RT.
The ORIENT parameter should be set to 0 if Isolid is 17. This is our recommended element type.
The ORIENT parameter should be set to 1 if Isolid is a co-rotational, except that ORIENT should be set to 2 if Isolid=18.
Radioss Isolid Types:
After the material model has been created, the Radioss FE model can be created as usual. Then insert the material model code into the rad-file.
Before running Radioss you need to copy the PolyUMod library to the same directory as the rad-files. The PolyUMod library is typically located here:
“C:\Program Files\PolymerFEM\PolyUMod_Altair\PolyUMod_Radioss\libraduser_win64.dll”. Or use the command line approach discussed in this document.
After the FE simulation has finished you can analyze the results as usual.
Here is a HyperView screenshot of the cylinder deformation example.
Shell Elements ( Example Test Problem )
Exemplar Problem
- A dogbone-shaped test specimen (consisting of shell elements) is pulled in tension.
- The goal of the analysis is to determine the stress in the test specimen as the part is being deformed.
- The files used for this example are located here:
C:\Program Files\PolymerFEM\PolyUMod_Altair\
TestCases_Radioss\TestCase_Dogbone_Tension_PolyUMod_BB_Shell
Use the MCalibration software to calibrate the Bergstrom-Boyce (BB) model to experimental data for the plastic material. The MCalibration software is discussed in more detailed in a separate tutorial.
From within MCalibration, export the calibrated material model parameters to a Radioss txt-file.
This is the contents of the exported material model. The material model is a type /MAT/USER01. The first 16 parameters are “control parameters” that specify certain behaviors of the material model. The remaining parameters are the material parameters.
The control parameters are discussed in detail in the PolyUMod User’s Manual (“C:\Program Files\PolymerFEM\PolyUMod_Altair\Documentation\PolyUMod_Manual.pdf”).
The following are the key control parameters that are used by Radioss:
- ORIENT: Should be set to 1 for shell elements.
- NPROP: Total number of control and material parameters.
- NHIST: Number of state variables that is used by the material model.
- GMU: Effective shear modulus. Is used to calculate the wave speed in the material.
- GKAPPA: Effective bulk modulus. Is used to calculate the wave speed in the material.
The ORIENT parameter controls how PolyUMod interprets the deformation gradient F that it receives from Radioss. If ORIENT=0, then PolyUMod assumes that F is in a global coordinate system. If ORIENT=1, then it uses the rotated RT F R. If ORIENT=2, then it uses the rotated R F RT.
The ORIENT parameter should be set to 1 for shell elements.
After the material model has been created, the Radioss FE model can be created as usual. Then insert the material model code into the rad-file.
Before running Radioss you need to copy the PolyUMod library to the same directory as the rad-files. The PolyUMod library is typically located here:
“C:\Program Files\PolymerFEM\PolyUMod_Altair\PolyUMod_Radioss\libraduser_win64.dll”. Or use the command line approach discussed in this article.
After the FE simulation has finished you can analyze the results as usual.
Here is a HyperView screenshot of the FE results.
Conclusions
The PolyUMod library contains many advanced material models that can be used in Radioss to accurately predict the response of polymers such as rubbers, thermoplastics, thermosets, and biomaterials.
Running a Radioss FE simulation with the PolyUMod library requires the following 3 simple steps:
- Calibrate a suitable material model using MCalibration.
- Export the material model into a Radioss file format.
- Import the material model into the Radioss input file and run the simulation.
