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

DSTO-RR-0208
Table 9: Residual Stress Results from X-ray Diffraction Technique.
Vertical
Direction
Base Line Peen
+ Surface
Treatment
+Surface
treatment+Heati
ng Treatment
-231 MPa -220 MPa -187 MPa
Horizontal -260 MPa -254 MPa -182 MPa
Direction
Average -246 MPa -237 MPa -185 MPa
Note: Specimens heated for 1 hour at 110 0 C, cooled to room temperature and then 2 hours at
120 0 C.
A slight drop was observed in mean surface residual stress readings. However, since the
fatigue are apparently not affected it is unlikely that a significant change in the residual
stress depth pr<strong>of</strong>ile has occurred. A recent test program conducted by QETE in Canada
(Roth and Yanishevsky 1999) supports these results.
3.5.2 Fleet Y470.5 X19 Pocket Repair program
AMRL proposed to the RAAF a fleet lifing policy for the X19 region based on its peening
specification and research into surface finish. <strong>The</strong> Y470.5 X19 pocket is a highly stressed
region (approx 420MPa) <strong>of</strong> the wing-carry through bulkheads. <strong>The</strong> X19 pocket failed during
the US Navy fatigue test ST16 and is regarded as a possible life limiting area in terms <strong>of</strong>
extending the operational life <strong>of</strong> the F/A-18.
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