Abstract
Tensile stress relaxation behavior at large deformations were further investigated for seventeen samples of raw, oil-extended and filler-loaded rubbers. The temperature range and the strain range tested were 35135°C and 0.15.0, respectively.
All of the samples were found to be thermorheologically simple irrespective of the magnitude of strain. Thus
S(t)=S0 (t/aT),
where S(t) and S0 (t) are the relaxation stress (true) at an arbitrarily chosen and a reference temperatures, respectively, and aT, shift factor, appeared to be little affected by the change in strain.
Time dependences of relaxation stress, S (t), in all samples were found to be expressed in the form,
S(t)=f(γ)∫∞-∞He-t/θd(lnθ)
where H represents the relaxation spectra which is a function of relaxation time, θ.
f(γ), the non-linear factor, is a function of strain, γ, and the following empirical equation was obtained.
f(γ) =aln[1+(γ/a)].
Here a is a factor independent of γ. The value of a appeared to be equal to unity for raw and oil-extended rubbers but smaller than unity in filler-loaded rubbers.
