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Published in:
01-12-2008 | Original Contribution
Strain energy function of an uncross-linked butadiene rubber estimated from planar extension
Published in: Rheologica Acta | Issue 9/2008
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Abstract
The derivatives of the strain energy function u with respect to the invariants of the strain tensor (I1 and I2) are estimated for uncross-linked butadiene rubber by using the BKZ constitutive equation. The derivatives at small deformations show anomalous behavior; namely, an upturn for ∂u/∂I1 and a downturn for ∂u/∂I2 take place, as is the case of cross-linked rubbers. At large deformations, u is well described by u = A1(I1 −3) + A2(I2 −3) with numerical constants A1 and A2. This behavior is also quite similar to that for cross-linked rubbers. The non-zero positive constant A2 for the melt suggests that the non-zero value is due to neither the inhomogeneity in network structure nor high extension of constituent polymer chains.