Review of Fatigue-Crack-Growth Prediction Methods

Empirical relations for describing constant-amplitude crack-growth behavior are reviewed. The effect of stress ratio (mean stress) on crack growth is illustrated through the use of plots analogous to constant-lifetime fatigue diagrams for 2024 Al, 7075 Al and Ti-6Al-4V. Experimentally observed load-sequence effects, such as crack retardation due to tensile overloads, acceleration due to compressive overloads, the interaction between tensile and compressive overloads, etc, are summarized. The crack-closure phenomenon is reviewed, since it seems to provide a plausible physical explanation for many sequence effects. Methods of predicting crack growth under variable-amplitude loading (including irregular loadings representative of actual service) are reviewed and some of their limitations noted. 50 ref.--AA.