Viscoelatic optimisation for hydrogel

[sri]

I am doing the visco-elastic optimisation for hydrogel. I am using the reaction force from the stress relaxation data as the objective function for optimisation. I did the experiment for 3000s. The peak force was around 0.07 N, and the force at 3000s was around 0.039N.
In one post, Prof Ateshian mentioned the g1, g2, and g3 selection based on the relaxation percentage. I referred to that post, used g1+g2+g3 as around 2, g0 and E as 0.08, v as 0.3, t1, t2, t3 as 500, 1500, 2000 roughly for the initial condition, and started the optimisation to optimise g1, g2, g3, t1, t2, t3.
End of optimisation, the solver suggests the maximum value as the optimal one. Is it reasonable to increase the time series greater than the experiment?, do I need to optmise g0 also, currently I took the E and g0 as equal.

If anyone has performed the viscoelastic analysis, kindly let me know the considerations for selecting the prony series to fit the stress relaxation data.

Thanks

[ateshian]

Hi,

As a general rule, g0 should be set to 1, even though the code allows it to be adjustable. That's because the equilbrium elastic response is proportional to g0 x E0, so it doesn't help to optimize both parameters. Please try g0 =1 and see what you find.

Best,

Gerard