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