Equivalent Fatigue Loading

(1)P A simplified equivalent loading shall only be used in place of a more realistic fatigue loading if the following conditions are satisfied:

a) The aluminium alloy structure shall fall within the range of basic structural forms and size for which the equivalent fatigue loading was originally derived.

b) The real loading shall be of similar intensity and frequency and be applied in a similar way to that assumed in the derivation of the equivalent fatigue loading.

c) The values of mi, m2, ND and NL assumed in the derivation of equivalent fatigue loading shall be the same as those appropriate to the detail being assessed.

NOTE: Some equivalent fatigue loadings may have been derived assuming a simple continuous slope where m2 = mi and AaL = 0. For many applications involving numerous low amplitude cycles this will result in a very conservative estimate of life.

d) The dynamic response of the structure shall be sufficiently low that resonant effects, which will be affected by differences in mass, stiffness and damping coefficient, will have little effect on the overall damage summation.

(2)P In the event that an equivalent fatigue loading is derived specifically for an aluminium alloy structural application, all the matters addressed in 3.3(1) shall be taken into account.

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