Figure 7. Loading ratio vs. cycles to failure graphs for (a)
6AL10a, (b) 6AL10b and (c) 6AL10c specimens
Figure 8 (a) shows cycles to failure values corresponding to different
loading ratios for the 6AL15b specimen. For all loading ratios, the
cycles to failure value of specimens damaged with 5 Joules of impact
energy was approximately 62% of undamaged specimens. Similarly, the
cycles to failure value for specimens damaged with 10 Joules of impact
energy was approximately 50% of undamaged specimens. This shows that
the relationship between impact energy and fatigue life is not linear.
Figure 8 (b) shows cycles to failure values corresponding to different
loading ratios for the 6AL20b specimen. The specimen affected most by
preliminary damage was 6AL20b. For r = 0.7, the preliminary damage
produced by 5 Joules and 10 Joules of impact energy decreased the
specimen’s life by 85% and 97.5% compared to that of the undamaged
specimen. Decreasing the loading ratio increased the life of damaged and
undamaged specimens.
Figure 8 (c) shows cycles to failure values corresponding to loading
ratios for the 9AL10b specimen. The static damage load of the specimen
for 5 Joules of impact energy was 1739 N, while it decreased to 1539 N
for 10 Joules of impact energy. When fatigue tests were performed at
90% and 80% of the static damage value for undamaged specimens, the
applied static loads were found to be 1750 N and 1550 N, respectively.
The static damage loads for specimens damaged by 5 Joules of impact
energy were below 90% of the static damage load of the undamaged
specimen, while those damaged by 10 Joules of impact energy were below
90% and 80% of the static damage load of the undamaged specimen. Thus,
the fatigue tests were not carried out at these loading ratios.