EVA - linear or non-linear viscoelasticity?!

[Amirb]

Hi,

I am working on EVA (Ethylene-vinyl acetate) to identify its viscoelastic properties I have done relaxation, creep and tensile test on it. I wonder if anybody has an idea hoe to recognize wether EVA is linear viscoelastic material or not?
Does normalizing the stress-Time (relaxation) help?

Thank you,

Amir

[Jorgen]

I recommend doing stress relaxation tests with different strain levels. If you get the same normalized stress relaxation response then the material is linear viscoelastic for those strains. :o

-Jorgen

[Amirb]

Jorgen,

I have done that and I have almost the same curves (Normalized stress vs Time).
I think even if it is not absoloutly linear I can consider it linear for small extensions.

Thanks,

Amir