Numéro : 2585 - Year : 2010
Welded joints fatigue strength improvement by post-weld treatments
Marc BOUSSEAU, DCNS – CESMAN
The design curves of as-welded components are independent of the yield strength of the steels used. The characteristic fatigue strength, at 2.106 cycles (FAT), does not exceed 100 MPa in case of a transverse butt weld. Such value can appear low for engineering and design departments. Studies relating to post weld improvement methods rely on two main principles: a)reduction of the severity of stress concentration (grinding, TIG dressing…), b)introduction of beneficial compressive residual stress (hammer or needle peening, shot peening, UIT, UP…). In both cases these methods are also applied to remove the flaws present in the weld toe. The improvement methods are intended for increasing the local fatigue strength or for repair or upgrading of existing structures. A brief presentation of the Recommendation IIW-1815-06 published 2006 is complemented by experimental results. Obviously, the effectiveness of the improved welds depends on the yield strength of the basic material. This point is important for using of high strength steels. Majority of experimental results for post weld treatment have involved constant amplitude fatigue loading. Influence of variable amplitude loading, important in service, is taking into account.
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