Abstract
The fatigue crack growth behaviour of short corner cracks in the Aluminium alloy Al 6013-T6 was investigated. The aim was to determine the crack growth rates of small corner cracks at a stress ratio of R = 0.1, R = 0.7 and R = 0.8 and to find a possible way to predict these crack growth rates from fatigue crack growth curves determined for long cracks. Corner cracks were introduced into short crack specimens, similar to M( T) – specimens, at one side of a hole (Ø = 4.8 mm) by cyclic compression ( R = 20). The precracks were smaller than 100 μm (notch + precrack). A completely new method was used to cut very small notches (10–50 μm) into the specimens with a focussed ion beam. The results of the fatigue crack growth tests with short corner cracks were compared with the long fatigue crack growth test data. The short cracks grew at Δ K-values below the threshold for long cracks at the same stress ratio. They also grew faster than long cracks at the same Δ K-values and the same stress ratios. A model was created on the basis of constant K max-tests with long cracks that gives a good and conservative estimation of the short crack growth rates.
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