Discussion on “the prediction of fatigue crack propagation under service load-time histories” by J. Schijve

The paper was abstracted from original as item 7412-61-0659. Results were reported for sheet center-notch panels subjected to flight simulation loadings. Five proportionately scaled load spectra with five corresponding ultimate design stresses and with five corresponding mean stresses in flight were chosen for test. The results for 2024-T3 Alclad and 7075-T6 clad are plotted. From the flight crack propagation rate vs stress intensity derivative an attempt is made to normalize stress level effects by considering the growth rates to be proportion to a mean flight plastic zone size. The reduction in data spread is encouraging but further improvements, especially for larger dK/da levels, should be sought, defining better the role of this parameter and its interaction with plasticity parameters. A mean plastic zone parameter might be conveniently incorporated into design practice.--EPAA/AF.