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

DSTO-RR-0208
Table 2: Four point bend tests to determine effect <strong>of</strong> a range a peening parameters quickly.
Treatment No. Gas Pressure Irradiation Bead Flux Bead Type
(Psi) Time (seconds) (m 2 /second)
1 74 40 1.2x10 7 Used glass
2 74 40 1.2x10 7 Fresh glass
3 74 19 1.2x10 7 Fresh glass
4 74 58 1.2x10 7 Fresh glass
5 95 40 1.2x10 7 Fresh glass
6 50 40 1.2x10 7 Fresh glass
7 30 40 1.2x10 7 Fresh glass
<strong>The</strong> results <strong>of</strong> these experiments are shown in figure 14.
Unpeened Treatment 1 Treatment2 Treatment3 Treatment4 Treatment5 Treatment6 Treatment7
7
6
5
4
Treatment
3
2
1
Unpeened
0 20000 40000 60000 80000 100000 120000 140000 160000
Fatigue life (Cycles)
Figure 14: Comparisons <strong>of</strong> hand-polish with various peening treatments looking at the effects <strong>of</strong>
peening process variables.
Treatment 2 is the standard treatment proposed for the RAAF aircraft, there is clearly a
significant life improvement over polished specimens and over used glass beads (treatment
1). <strong>The</strong> fatigue life improvement is the same for treatment 2 and 3, despite treatment 3
having 100% coverage compared to 200% coverage. An increase in coverage (300%)
treatment 4 shows a reduction in life compared to treatment 2 and 3. This is the “over-peen”
case. Gas pressure seems to have little effect on mean fatigue life except in terms <strong>of</strong>
increasing the fatigue life scatter for the lower pressures.
<strong>The</strong>se simple tests showed that the peening parameters DSTO needed to examine in detail to
provide a LIF for the RAAF fleet were Almen Intensity and coverage.
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