1983 Volume 32 Issue 355 Pages 378-382
The comparison in crack tip plastic stretch between the fatigue and the ideal cracks was made with special attention to the plasticity induced crack closure phenomenon during fatigue crack growth. By using this result, a model to evaluate transitional behavior from the fatigue crack to the ideal crack was proposed. The results obtained are as follows:
(1) For a given stress intensity factor, K, the ratio of the fatigue crack tip plastic stretch to that of the ideal crack is nearly 0.13. With this value, the ratio of the crack opening stress intensity, Kop, to the maximum stress intensity, Kmax, can be predicted as Kop/Kmax=0.58.
(2) When a single peak overload is applied to the fatigue crack, transitional behavior from the fatigue crack to the ideal crack occurs. A model to evaluate this behavior is proposed using the predicted Kop/Kmax value. Predicted values from this model showed a good agreement with the experimental results for several stress ratios, R.
(3) This model and the experimental results suggest that a fatigue pre-crack condition for the fracture toughness test adopted in the standards of the Japan Scociety of Mechanical Engineers, S001, and of the ASTM, E399, is reasonable.