CANCELLED: Lifetime prediction of elastomers - A unification of the fracture mechanics and the (Wöhler) s-n-concept

In recent years parts made of elastomers were more frequently used in complex technical fields which require high performance in terms of service life. Therefore it is very important to have an instrument to estimate the service life of these technical parts. At the moment there are two classical approaches for service life prediction. Both are more or less adapted from metal parts engineering. Fracture mechanics uses the characteristic values of dynamic crack propagation experiments to calculate the load cycles to failure for different load amplitudes. The other method, based on the concept of Wöhler measures the lifetime of laboratory samples at different load amplitudes (fatigue to failure tests, s-n curves). Both are useful for specific applications. But they can lead to different results or rankings if several elastomer materials are compared. In this work an approach is shown how to combine or unify the two classical methods. An important prerequisite for the fracture mechanics calculations is the knowledge of the initial crack or flaw sizes within the elastomer material. High resolution x-ray computer tomography (CT) as a new method to characterize these structures is presented. It will be shown that fracture mechanics calculations starting with the flaw size distributions directly lead to s-n- or Wöhler-curves. Furthermore, the probability of early failures can be predicted which is of high practical importance. The results of the calculations and of the experimental work on elastomer materials differing in carbon black dispersion will be discussed.