Stiffness and temperature

[Muzialis]

I am dealing with a rubber component generating quite a large amount of heat in its cyclic behavior. I was pretty sure stiffness is supposed to increase with temperature (proportionally according to kinetic theory) and I was surprised to obtain completely different test data. NR based black filled compounds were tested and regradless of the carbon content all of them showed a slight but still noticeable decrease in stiffness in the range -20 C - +30 C.

I understand the theory is an idealization, but still I am getting concerned about the testing as it was performed externally in quite a rush.

Am I just relying toom uch on general principles and panicking uselessly?

Thank you

Muzialis

[Jorgen]

The traditional (simple) hyperelastic theory is based on entropic elasticity and predicts that the stress (at any value of strain) is proportional to the absolute temperature in Kelvin. Well, it turns out that real rubbers and elastomers do not typically behave like that. In fact, many filled elastomers (including NR) becomes less stiff as the temperature increases.

Your experimental data seem OK to me.

- Jorgen

[Muzialis]

Jorgen,

thank you again as usual.

All the best

Muzialis