Abstract
The fatigue crack growth and threshold behavior of AA2219 Al-alloy has been examined for naturally aged (NA), under aged (UA), peak aged (PA) and over aged (OA) conditions. Significant differences were observed in the fatigue crack growth at low and high stress intensity ranges. The alloy in the NA condition possesses the highest resistance to fatigue crack initiation which can be viewed from the values of achieved threshold stress intensity range, ΔKTH. In the intermediate ΔK (Paris law) regime, all the four materials fall into a single band. In the high ΔK regime (> 20 MPa√m) PA condition exhibits better crack growth resistance than under aged conditions. The inhomogeneous transcrystalline slip in the UA condition results in the slower crack growth at low ΔK. The fracture morphology changes from crystallographic facets in the threshold region to clearly developed ductile striations in the Paris law regime to microvoid coalescence in the high ΔK region.
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