Hello,
I am working on a continuum project attempting to implement the BB model for PTFE material. I am inquiring about Network B in this model. I am not certain where the Fe deformation matrix is coming from. It is not explicitly stated in Bergstrom, Boyce (2005) paper. I am trying to match the model to experimental data using MATLAB. Could anyone provide some assistance?
Thank you,
Kate
Hello Kate - Welcome to the forum 😀
I am not sure I fully understand your question. If your goal is to calibrate (find) the BB model parameters that match some experimental data, then I would recommend you using the MCalibration software. It is very easy to use, and you can get a free trial license by clicking on the button on the front page of PolymerFEM.com
If your goal is to create your own implementation of the BB model then I recommend that you read my Polymer Mechanics book, which contains (I think) a Python implementation of the BB model.
If you have a specific question about the Fe tensor, then can you please provide a bit more details here?
-Jorgen
Hello Jorgen,
Thank you for your response. In regards to the Fe tensor, I am having difficulty understanding where to take data from. In particular, I am utilizing the (2005) paper to try and replicate your stress-strain plots for PTFE at -53 C. While using the BB model, network B calls for the 8-chain model (same as network A) except now the Fe deformation matrix is being used. I am not exactly certain how to get this tensor. I am using the function Grabit in MATLAB to get data from the plots in order to try and replicate them via the BB model. When I attempt to model this data in MATLAB, my plot does not look as it should and I think the issue revolves around the deformation matrices. Hopefully that gives a little more specificity for the question.
Attached are the plots I am attempting to replicate.
FIGURE 1: I am pulling data from the -53 C curve and using the true strain to form the F tensor.
FIGURE 2: Pulling data from this curve to generate Fe matrix?
FIGURE 3: My plots from MATLAB
Thanks for the images. I am starting to understand your question. You are right, the F tensor can be determined from the applied strain (well, at least the F_11).
The way to determine the Fe tensor is from:
\(\mathbf{F}^e = \mathbf{F} \left( \mathbf{F}^p \right)^{-1}\)
That is, you need to first calculate the Fp tensor (from the flow rate equation), and then you can calculate the Fe tensor.
-Jorgen