Stress ratio and the fatigue damage map—Part I: Modelling

In this work, the effect of the stress ratio R on the five areas that constitute the fatigue damage map is presented. The effect of R on crack arrest is modelled through the Kujawski’s empirical parameter α. The idea of matching crack growth rates was used to predict the effect of R on the transition from Stage I to Stage II growth. The transition from Stage II to Stage III was modelled through its direct relation to R. Finally, the areas of general yielding and toughness failure were modelled through the relationship between Δσ and R. The accuracy of the modelling for each area is validated with experimental results.