The Effect of Peening on the Fatigue Life of 7050 Aluminium Alloy

DSTO-RR-0208
It should be noted that the saturation <strong>of</strong> the Almen strip and coverage <strong>of</strong> the part are not the
same, nor will they necessarily occur at the same exposure time on the parts being peened.
Saturation is a function <strong>of</strong> the energy <strong>of</strong> the shot stream and establishes the actual intensity
for the particular machine set-up.
Saturation should not be confused with coverage, which refers to the population <strong>of</strong> dimples
on the surface as verified by coverage inspection techniques. Coverage is usually expressed
as a percent coverage (eg 100% coverage). 100% coverage is reached when the original
surface <strong>of</strong> the material is obliterated entirely by overlapping peening dimples. 150%
coverage would be exposing the part to 1.5 times the time required to achieve 100%
coverage. In the case <strong>of</strong> F/A-18, 200% coverage is specified for all peening work.
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