Figure 9. Loading ratio
vs. cycles to failure graphs for the (a) 6CFRP10a, (b) 6CFRP10b and (c)
6CFRP10c specimens
Fatigue crack didn’t observed during fatigue tests due to loading type.
Core crushing failure is the main failure type for all fatigue
specimens. No failures observed for adhesive between core and face
material. Adhesion tests can be investigated in future studies.
4.3. Damping Ratio and Stiffness
Reduction
Damping indicates the amount of energy required to rearrange molecules
of the material due to internal friction. The energy consumed by the
material due to internal friction and movements is called the loss
modulus (E’), while the response energy consumed by the material against
impact is the damping modulus (E”). The damping ratio is calculated by
the formula tan (δ) = E”/E’, and it is independent of geometric
effects.
To determine the amount of energy absorbed by specimens after the
fatigue tests, tan (δ) vs. cycles to failure (log N) graphs are shown
below.
Figure 10 shows the effect of different loading ratios on the damping
ratio for the undamaged 6AL10b specimen under three-point bending loads.
The damping ratio decreased with increasing loading ratio, while for all
loading ratios, minimum damping ratios were determined at cycles to
failure values where fatigue damage occurred.