(1) The largest benefits are normally obtained with methods where compressive residual stresses are introduced. The most common methods are hammer peening, needle peening, and shot peening. Peening is a cold working process where the impact of a tool deforms the surface plastically. The surrounding (elastic) mterial will compress the deformed volume. High compressive service loading can decrease the level of residual stress and must be taken into account when applying random loading spectra.

(2) Procedures for all peening methods must be worked out: Passes, weld toe deformation, and indentation for hammer and wire bundle peening; intensity, coverage, and Almen strip deformation for shot peening.

Annex F (informative) Low Cycle Fatigue F.1 Introduction

(1) Where significant damage is done by high stress ranges which are applied less than 105 times, the Act-N curves given in 5.2 for certain details and R-ratios may be unnecessarily conservative. The data below may be used to obtain a more accurate life prediction.

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