Improvement Techniques

(1) The fatigue strength of certain detail types shown in tables 5.1.1 to 5.1.5 may be improved by the application of special manufacturing techniques. These are generally expensive to apply and present quality control difficulties. They should not be relied upon for general design purposes, unless fatigue is particularly critical to the overall economy of the structure, in which case specialist advice should be sought. They are more commonly used to overcome existing design deficiencies.

(2) The following techniques have been used on aluminium alloys and are most effective for high cycle applications.

a) Introduction of compressive residual stresses at the location of crack initiation. This may be carried out at transverse weld toes by peening. At bolt holes the cold expansion method may be used.

(b) Reduction of stress concentration effect at the location of crack initiation. This may be carried out by grinding transverse weld toes to a smooth profile.

(3) Further information on improvement techniques is given in Annex E.

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