Fatigue crack closure: From LCF to small scale yielding

Most of the research on crack closure has been devoted to crack propagation under small scale yielding. In this paper, the effect of different length scale from micro-crack to long cracks and different loading conditions from low cycle fatigue, LCF, to small scale yielding on crack closure are considered. The main focus is on LCF crack closure behaviour which is studied by in situ fatigue experiments in a scanning electron microscope. The results demonstrate the importance of crack closure for the explanation of the LCF behaviour. The change of crack closure from LCF to high cycle fatigue and their consequences for lifetime prediction will be discussed.