Viscoelastic behavior of rubber under a complex loading

Abstract

AbstractIn the literature, the loss factor of an elastomer, expressed as tan δ, has been reported to decrease with strain. This has been interpreted as a lowering of the internal viscosity due to chain orientation under strain. This contrasts with experimental findings showing that up to large strains, loss modulus does not change with strain. These experiments show that, as measured, tan δ does decrease with strain. However, a simple analysis shows that this effect is due to geometric changes alone and that the essential viscoelastic behavior, expressed as the loss modulus, is constant with strain up to an extension of about 2 for the simple unfilled compounds investigated here. This article also shows that the prestrain does not induce any significant anisotropy in the loss modulus, at least up to an extension ratio of 2. This was measured by the stretching of a rubber sample by simple extension and then the subjection of the sample to free vibrations in either torsion or tension. By the measurement of the damping in this way, the anisotropy induced by the pre‐extension was measured. The experiments in this work were all conducted on unfilled natural rubber or styrene–butadiene rubber compounds, with 2 different natural rubber compounds being used to investigate the effect of the crosslink density. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009