Influence of the Temperature on Lifetime Reinforcement of a Filled NR

Abstract

Fatigue of crystallizable rubbers has been widely investigated since the pioneer work by Cadwell et al. in 1940 (Cadwell et al., Ind Eng Chem 12:19–23, 1940). This study revealed the significant influence of the mean strain on natural rubber lifetime: for non-relaxing loading conditions (i.e. R > 0), strong lifetime reinforcement was observed and attributed strain-induced crystallization (SIC). Better understanding how SIC reinforces fatigue life is therefore a key point to improve the durability of rubbers. Surprisingly, few studies investigated the effect of temperature on the lifetime, while SIC exhibits a high thermo-sensitivity (Lindley, Rubber Chem Technol 47:1253–1264, 1974; Lu Etude du comportement mecanique et des mecanismes d’endommagement des elastomeres en fatigue et en fissuration par fatigue. PhD Thesis, Conservatoire National des Arts et Metiers, 1991). The present study aims therefore at investigating how temperature affects the fatigue life reinforcement due to SIC under non-relaxing loading conditions. First of all, fatigue tests are carried out at 23 °C. Damage leading to the end-of-life is investigated at both the macroscopic and the microscopic scales for loading ratios from −0.25 to 0.35. As expected, NR exhibits a reinforcement for positive loading ratios R at 23 °C. Damage, striations due to SIC and number of cycles at crack initiation are mapped using the Haigh diagram. At 90 °C, the fatigue lifetime reinforcement is lower and the signature of SIC on the failure surface disappears. The competition between non-relaxing loading effect and temperature is finally discussed.