Threshold and effective threshold of fatigue crack propagation in ARMCO iron II: The influence of environment

Abstract

The crack growth behaviour in the near threshold region was studied in ARMCO iron at different oxygen pressures and in ultrahigh vacuum. The effect of crack closure was examined and compared with the results in air. It is shown that the effective threshold of stress intensity range is not very significantly influenced by the environment. However, the d a/d N vs. ΔK eff curve in ultrahigh vacuum is much lower than in air. The transition of the crack growth behaviour in air to that in ultrahigh vacuum occurs at a relatively low exposure per cycle of oxygen.