Crack closure and growth behavior of physically short fatigue cracks under random loading

Crack closure and growth behavior of physically short fatigue cracks under random loading are investigated by performing narrow- and wide-band random loading tests for various stress ratios. Artificially prepared two-dimensional, short through-thickness cracks are used. The closure behavior of short cracks under random loading is discussed, comparing with that of short cracks under constant-amplitude loading and also that of long cracks under random loading. Irrespective of random loading spectrum or block length, the crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history, contrary to the behavior of long cracks that the crack opening load under random loading is nearly the same as or slightly higher than the constant-amplitude results. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks. Fatigue crack growth of short cracks under random loading can be well described by the crack closure concept, as well as under constant-amplitude loading.