Crack opening displacement and propagation rate of microstructurally short cracks

Crack opening displacement (COD) along the edges of microstructurally short fatigue cracks in austenitic stainless steel was investigated in situ in the SEM. The measured plastic part of the COD range between maximum and minimum load was extrapolated to the near crack tip region, assuming plastic blunting and resharpening by cooperative slip as well known for long cracks. In accordance with the blunting model, the measured crack propagation per cycle is about the half of the extrapolated plastic COD range.