Both short and long fatigue crack growth in an austenitic stainless steel at 650 degrees C

Continuous fatigue tests in a 316L(N) stainless steel at 650 degrees C are conducted on notched and pre-cracked CT specimens. Fatigue crack growth analysis of both type of specimens reveals two different behaviours. Cracks emanating from notched specimens exhibit a characteristic short crack behaviour whereas propagation of long cracks from pre-cracked specimens are significantly influenced by the stress ratio R. Differences between short and long fatigue cracks are analysed using the crack closure concept. An experimental measurement of the closure level K-op using an elastic compliance method can explain both behaviours. A relationship between measured crack opening stress ratio U and stress ratio Ris also proposed.