SHORT FATIGUE CRACK GROWTH IN PLAIN AND NOTCHED SPECIMENS OF AN 8090 Al-Li ALLOY

Abstract— Fatigue tests on notched and plain specimens were carried out under a combined acoustic and optical microscope. Crack initiation in plain specimens occurs invariably at inclusions which act as sites of stress concentration. Short crack propagation behaviour shows the usual pattern of accelerations and retardations associated with microstructural variations. Growth can only be sustained if the applied stress is sufficiently high to overcome the microstructural barriers. For the notched specimens the extent of the notch tip and crack tip plastic zone sizes control crack propagation. A short crack will continue to propagate only if its own plastic zone can sustain growth as the crack tip extends beyond the notch zone, otherwise it becomes non-propagating. Notch plastic zones are calculated using both approximate and accurate solutions. Some microstructural effects are discussed.