Journal Papers Published by the Rubber Research Group
"The visco-elastic behaviour of elastomers at large pre-strains "
Journal: Constitutive Models for Rubber VI edited by G. Heinrich, M. Kaliske, A. Lion & S. Reese, pp. 153-157.
Kuhn and Kunzle (1955) explained that the reduction in loss angle for small oscillations with increasing pre-strain resulted from the molecular rearrangement of the polymer. In contrast, Suphadon et al. (2009) showed that the loss angle decreased due to changes in geometry alone and that the loss modulus was constant for a wide range of unfilled materials up to quite large strains. They also found that for a range of unfilled rubbers that a pre-strain, of up to 100% strain, did not induce any anisotropy in the loss modulus behaviour when measured using small strain oscillations superimposed on the larger pre-strain. From this work it was clear that the energy dissipation depended only on the geometric shape of the sample and not on the pre-strain. This paper extends the previous work to larger pre-strains for SBR (styrene butadiene rubber) and NR (natural rubber) compounds some of which incorporate fillers. The results show for materials that with 25 phr of carbon black filler, the loss modulus is still independent of the pre-strain for normal working strains but at filler contents of 50 phr, the loss modulus increases with pre-strain at extension ratios lower than 2. This probably results from the significant effect of the strain amplification which arises at higher filler volume frac-tion. Additional experiments to investigate the effect of the load history and anisotropy in the loss modulus with pre-strain are also described.