Fatigue behaviour of an elastomer under consideration of ageing effects

Due to their vibration isolation performance, elastomers are often used in industrial applications such as bearings or seals. In service, parts made of rubber are often exposed to high temperatures while undergoing dynamic mechanical loads. On the one hand, this may reduce the fatigue properties in an irreversible manner due to thermo-oxidative network degradation and reformation, which is known as chemical ageing. In a durability test at constant temperature, a rubber specimen that was already aged at elevated temperatures exhibits a different fatigue behaviour than an unaged specimen of the same material. Since this behaviour is determined by the temperature history prior to the durability test, it is an indirect effect. If, on the other hand, durability tests of unaged specimens are carried out under different elevated temperatures, the temperature also has an instantaneous effect on the material's lifetime. This direct effect vanishes if the temperature is reduced to a certain level. This work deals with both the indirect (chemical ageing) and the direct effects of elevated temperatures on the fatigue life of a natural rubber (NR) under mechanical loads. Therefore, fatigue tests were performed to investigate the various effects of elevated temperatures on the fatigue life. A new model is proposed that takes into account these effects. This model may therefore help establish more realistic test procedures for component development and provide relevant information for improved fatigue life prediction concepts.