I am using MCalibration software to calibrate the BB model for our elastomer. I have two sets of uniaxial compression test data with different strain rates for this purpose. The calibration, as I was expecting, depends on the initial values of constant. I have tried changing the parameters manually to get the prediction closer to the test data, however the software calibration does not give me a good fit for the manually manipulated initial values.
I would like to know if there is any rule of thumb for initial values for the uniaxial tests.