Effect of temperature history on the mechanical behaviour of a filler-reinforced NR/BR blend: literature review and critical experiments

The influence of the temperature history on the Mullins effect, its recovery behaviour and the rate dependence is experimentally investigated using NR/BR (NR: natural rubber, BR: polybutadiene rubber) rubber blend. The crystallization which occurs in rubber during long term storage below the melting temperature has been taken into account to interpret the experimental data. To study the influence of low temperatures and large deformations on the Mullins effect, cyclic strain-controlled processes are applied under different temperatures. The softened specimens are subjected to a sequence of heating, cooling, and conditioning processes in order to study the influence of the temperature history on healing, melting, and recrystallization. The results indicate the existence of a threshold temperature: if the specimen temperature is larger than this threshold, a nearly complete recovery of the material occurs within finite time, while any temperature below this limit will be too small for healing. The temperature dependence of both the healing and the Mullins effect in rubber with different degrees of crystallinity is resolved by considering the melting and recrystallization rates. The rate dependence of the blend is investigated under different temperatures via monotonic and cyclic tension tests at different strain rates and relaxation tests. The experimental data suggests a decrease in the strain rate sensitivity at higher temperatures. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim