Estimation of Stress-Strain Curves of Rubber Vulcanizates by Crosslink Density

The following stress-strain relation was used for the estimation of the stress-strain behavior of rubber vulcanizates: f={G-B(1-1/α)+C(α2-1)+D(α+1/a2-2)+F(α4-1)}(α-1/α2) where f is nominal stress at an extension ratio α, G corresponds to rigidity, B, C, D, and F are coefficients. The experimental stress ·strain relations of all rubber vulcanizates used in this study coincided with the above relation in the extension range almost up to the break. It was found that there existed a unique functional relation between each coefficient and the crosslink density, and the functions were determined as polynomial functions of the crosslink density. Rubber vulcanizates used were natural rubber (NR) with various contents of sulfur ranging from 0.5 to 4.5 PHR, styrene-butadiene rubber (SBR) with various concentrations of carbon black filler (SAF), and also SBR with various concentrations of oil.