有限変形下における加硫SBRの力学的性質

抄録

The stress relaxation properties of SBR vulcanizates, those unfilled and those filled with carbon, under orthogonal-biaxial deformation, were subjected to observation in a region from 3.4 to 10 of I₁ values where I₁ was invariant of deformation tensor, and the contour maps of ∂W/∂I₁ and ∂W/∂I₂ were obtained as functions of time t. The following results have been obtained.
The time dependence of both ∂W/∂I₁ and ∂W/∂I₂ of the unfiilled SBR vulcanizate are very similar within experimental error, but in the case of the filled SBR, those are quite different. In the filled SBR, the relaxation rate of ∂W/∂I₁ decreases with increase in I₁, and on the contrary, the rate of ∂W/∂I₂ increases with increase in I₁. The shape of ∂W/∂I₁ surface of the filled SBR is similar to that of the unfilled SBR, but the former is on a considerably higher level than the latter, while the shape of ∂W/∂I₂ surface of the filled SBR is different from that of the unfilled SBR.
The values of ∂W/∂I₁ and ∂W/∂I₂ in the uniaxial deformation are obtained by the extrapolating method using the biaxial data. It is shown that the values of ∂W/∂I₁ and ∂W/∂I₂ in the uniaxial deformation decrease with increase in deformation. In this fact is suggested that strain energy function W cannot be estimated by Mooney-Rivlin plot, and that the constants C₁ and C₂ obtained from the plot are almost of no significance.