Figure 10. Tan (δ) vs. Log (N) graph for the 6AL10b specimen

Figure 11 (a) shows damping ratios of the 6AL10b and 6CFRP10b specimens at a loading ratio of r = 0.6. At the same loading ratio, the damping ratios of the aluminum specimen were found to be higher than those of the CFRP specimen.
Figure 11 (b) shows the normalized cycle – Stiffness reduction graph for 6AL10b and 6CFRP10b specimens. Stiffness calculated as maximum applied load divided by maximum deflection for every cycle31. Stiffness change with fatigue cycle shows the same trend with damping ratio graphs. While normalized fatigue cycle approaching the 1, stiffness decreases and dramatical stiffness reduction observed at the end of lifetime.