Effect of cyclic plastic strain on fatigue crack growth

• Short fatigue cracks open and close at nearly the same global strains.
• The effective cyclic ΔJ-integral well correlates short fatigue crack growth rates.
• Acceleration dominates in variable amplitude loading with large plastic strains.
• Short fatigue crack growth calculations for multiaxial loading are performed.

Because fatigue life calculations, which are based on the stress intensity factor, are restricted to certain limited applications, one must develop substitute procedures in more general settings. Various proposals for a crack driving force parameter in elastic–plastic fracture mechanics will be discussed. A preference in favour of the cyclic ΔJ-integral is elaborated, keeping its theoretical limitations in mind. Crack closure is also an important issue under large-scale yielding conditions. Experience cannot be extrapolated from the small-scale to the large-scale cyclic yielding regime or vice versa. The consequences for fatigue lives under variable amplitude and multiaxial loading are discussed.