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Subcritical crack growth under static and cyclic loads is an important failure mode and often responsible for delayed failure. At least for subcritical crack extension under constant load it is a well-known fact that the crack growth behaviour of natural cracks differs significantly from that of macroscopic cracks, especially for such materials exhibiting a pronounced R-curve behaviour. The influence of bridging surface interactions — responsible for R-curves in alumina (Al2O3) — will be discussed with respect to strength and static lifetimes. Experimental results obtained for both loading cases are presented for alumina. Measured lifetimes are significantly shorter than the predictions and a reduction of lifetimes is found for increasing frequencies. From these results an effect of cycles becomes obvious and it can be concluded that a real cyclic fatigue effect occurs.
Static fatigue, cyclic fatigue, lifetime prediction, R-curve effect, bridging interactions, coarse-grained alumina (, Al2, O3, )
Research Engineer, Kernforschungszentrum Karlsruhe, Institut für Materialforschung II,
Professor, Universität Karlsruhe, Institut für Zuverlässigkeit und Schadenskunde im Maschinenbau, and Kernforschungszentrum Karlsruhe, Institut für Materialforschung II, Karlsruhe,