Large Elastic Behavior and Fracture of Oil-Extended SBR Vulcanizates

Abstract

Hereunder is presented a brief report of the test concerning the applicability of the following stress-strain relation f=(A+B/α+Cα2)(α-1/α2) to the stress-strain behavior of styrene-butadiene rubber (SBR) with various concentrations of oil ranging from 0 to 40 PHR, and the dependences of the values of A, B and C on oil concentration, sulfur content (crosslink density) and strain rate were examined. In the above relation, f denoted the tension at extension ratio α, A, B and C were coefficients. This relation had been obtained from the phenomenological theory of finite deformation with second order approximation to the stored energy function. The time-concentration equivalence of the ultimate properties of the data was also examind. The samples of SBR were sulfur cured with various contents of sulfur in the presence of oil at 155°C for 60 minutes. The stress-strain data were determined by means of an Instron type tester at various crosshead speeds between 8mm/min and 800mm/min at the temperature 20°C. The results will be summarized as follows:(1) The values of A decreased with increase of oil concentration and increased with sulfur content and they were unaffected by the strain rate.(2) The values of B decreased with increase of oil concentration and were almost unaffected by the sulfur content, and they showed slight increase against the strain rate at high strain region.(3) The values of C were very small and almost 0 for the data at crosshead speeds below 200mm/min. They decreased with increase of oil conentration and had the maximum aginst the sulfur content and also against the strain rate.(4) Stress at break σb data of samples with different oil concentrations could be represented by a master curve by applying the method of time-concentration superposition, and the shift distances log ac obtained superposing data followed the theory of solution type equation.