Abstract
The split-sleeve cold-expansion process was applied to hot-rolled 1020 steel specimens containing a central notch and a central notch plus an EDM corner notch. The EDM notch was made to simulate a small corner crack in the notch. Constant amplitude axial fatigue tests were performed in the as-machined condition and the cold-expansion condition with the stress ratio, R, equal to 0.05 and −1. Fatigue life improvement occurred in the cold-expansion specimens at lower stress amplitudes in three out of four test series. EDM specimen crack growth monitoring indicated that the life improvement was due to small increases in crack initiation life (crack length equal to 0.25 mm) and to a larger extent fatigue crack growth retardation. Cyclic relaxation of residual compressive stresses due to higher stresses was the apparent reason for those cases where fatigue life improvement did not occur. SEM fractographic analysis of EDM specimens showed similar fatigue crack growth morphology for all test conditions.
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