Finite deformation behavior of elastomers - Dependence of strain energy density on degree of crosslinking for SBR.

Abstract The non-linear mechanical behavior of styrene-butadiene rubbers (SBR) having five different crosslink densities (νe) has been determined in large deformation biaxial stress-relaxation tests of thin-sheet specimens. A significant experimental development was the use of individual strain gages at the specimen support points to determine directly the stress distribution in the web. The tests indicated the separability of strain and time effects for extension ratios up to 3.0 for the most lightly crosslinked SBR. Long-time data showed the equilibrium shear modulus Ge to be directly proportional to νe. The ratio W/Ge was independent of crosslinking so that the strain energy density W has the same functional strain dependence for all SBR systems.