Fatigue crack closure and fatigue thresholds

The occurrence of plasticity-induced crack closure during fatigue has been questioned by Vasudevan and Sadananda, who have suggested that fatigue crack growth should be classified by two parameters, and that the differences between short and long crack growth are explained in terms of residual stress. These proposals are examined carefully, and it is concluded that, while the two parameter approach is a useful one, plasticity-induced closure effects are real and must be taken into account.