Influence of the loading conditions on fatigue properties for filled elastomers

Abstract

International audienceFatigue characterisation of elastomers is an essential prerequisite of new car project schedules imposed by carmakers. Consequently, durability prediction softwares are needed to reduce the time allowed to design elastomeric parts. Until now, the only theoretical variable used to predict duration life is the tearing energy proposed by Rivlin and Thomas. Classically, fatigue properties are determined using plane stress experiments (trousers or pure shear samples for example) under simple loading conditions. In the present paper, a brief bibliographical review presents the limitations of this approach and the need of more complex loading conditions is emphasised. Then, a new simple shear sample is proposed to simplify the treatment of experimental results, said the calculation of the tearing energy, under complex loading conditions. The test sample is initially notched and is submitted to controlled displacement loading conditions. The procedure adopted to analyse the results is presented. Assuming that the tearing energy and the crack growth rate remain constant during the test, they can be easily calculated using both the decreasing stiffness of the sample during the test and a FE model. Note that no complex system, such as video recording, is necessary to measure the crack length. Then, experimental results are reported. Both filled crystallising and non-crystallising elastomers are studied in order to highlight the influence of the testing temperature and of the imposed displacement ratio (i.e.: minimum/maximum displacement) on the fatigue crack growth rate law. This fatigue crack growth rate law obtained agrees well with previously published papers. Furthermore, other complex tests are in progress to determine the influence of the Mullins stress-softening on fatigue properties. Finally, in regards with these results, it is demonstrated that the tearing energy is not a sufficient variable to completely characterise the fatigue life of elastomers