I'm trying to reproduce the uniaxial rate dependent stress with help of the eight chain model in MatLab.
As said in "Large Strain Time-Dependent Behavior of Elastomeric MAterials" by Jorgen Bergstrom, the stress is composed of an equilibirum response and a time dependent response.
Modeling the equilibrium response (network A) is not too difficult, but I don't know how to implement the time dependency of network B.
Also I don't know why constant C3 and C4 are not given (in the aformentioned paper), since they are needed to determine the effective chain stretch, in for instance fig 5-11.
The formula for the effective chain stretch contains: time^C4, which would mean that equation 5.7 will grow unbounded over time.
Can anyone help me with this implementation and questions? Perhaps with an example of coding or something?
Thanks in advance