Hello Sangrey,

It is necessary in ANSYS to use Prony shear coefficients (That's how Ansys works). I guess the reason is that with those coefficients, we have a function (a curve) for Shear Modulus - Time relation, meanwhile from experiments we only have some discrete data.

Regarding 'what is different about 3 and 4 terms' check bsista comment on this post.

I am not sure if you have to use creep options, but if yes then check this from Peter.

Firstly, Fig 3 represents also the values in between and therefore 7 Prony parameters. bsista said that we can use 1s, 1e3s and 1e7s to have only 3 prony shear parameters and still have a good distribution of time (and therefore a better curve fit).

I hope it helps a bit.