Introduction - FEA of Teflon Seal
Teflon (PTFE) is commonly used in many seal applications due to its chemical resistance and low friction. One common challenge when designing a PTFE component, including a Teflon seal, is the highly non-linear viscoplastic response. The material undergoes significant stress relaxation, creep, and viscoplastic flow even at low applied stresses. The PolyUMod library contains many advanced material models that are excellent at predicting all of these behaviors, for example, I often use the TNV model. The main problem with this approach is that it requires carefully obtained (smart) experimental data for the specific PTFE material, which can be time consuming to obtain. For this reason, it is sometimes useful to use an advanced pre-calibrated material model for a generic PTFE. The PolyUMod Material Database contains a pre-calibrated advanced material model for a generic PTFE that you can use without having to run any experiments!
Here are the steps to use the PolyUMod Material Database in Ansys:
Step 1: Export the Material Model from MCalibration
Open the material model selection dialog box (1) and select the desired pre-calibrated material model from the PolyUMod Material Data Base. Then click on Export Model (2) and save the model as either a Workbench Engineering Data XML-file, or as an Ansys APDL dat-file.
Step 2: Assign the Material Model in Ansys Mechanical
One easy way to use the pre-calibrated PTFE material model is to paste in the contents of the dat-file that was exported from MCalibration into a command object for the part of interest. Another way is to import the MCalibration exported XML-file into Workbench Engineering Data, and then assign it in Mechanical from the list of materials.
Step 3: Run the Ansys FE Simulation
The following image shows contours of Mises stress from a compression simulation of the Teflon seal. The stress history at the bottom of the figure shows that the max stress of 110 MPa relaxes down to 20 MPa after 10 minutes. That is a very significant stress relaxation that cannot be predicted unless you have an advanced viscoplastic material model!
Here is the Ansys file that I used:
Here is a video that shows the details: