The effects of peening and hole expansion on the fatigue behaviour of 7079-T652 aluminium alloy

Report (1974)
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Fatigue Residual stress Shot peening Glassmbead peening Hole expansion Sub-surface crack initiation
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Published Date

31-01-1974

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NLR-TR 74016 U

Abstract

The effects of shot and glass bead peening and hole expansion on the direct stress fatigue life of 7079-1'652 aliiminium alloy specimens are considered. Three types of specimens were employed: unnotched, notched by a central hole and notched at comers. Shot peening was only slightly beneficial for high cycle fatigue, and then only for comer notched specimens. Glass bead peening (at 3 A) was more beneficial than shot peening (10 A) for unnotched specimens. Hole expansion proved to be significantly beneficial for specimens notched by a central hole. Practographic and metallographic examinations of the specimens led to the conclusion that some cracks originated internally. Detailed examination of one of these cracks revealed characteristics of fatigue in an inert environment, presumably vacuum. Prom these examinations and the measurement of residual stresses induced by shot peening a rationale is presented for the fatigue life observations, and some suggestions are made for further work, including different materials