Figure 12. Tan (δ) vs. Log (N)
graph for the 9AL10b
specimen
Conclusion
The results obtained after three-point bending, low velocity impact,
three-point bending after impact, fatigue and fatigue after impact tests
are evaluated below:
- For three-point bending loads, increasing the core height increased
the damage load of the specimen. With increased core height, damage
was concentrated on the zone affected by the load. For the three core
height values, debonding damage was seen between the core and the face
sheet; buckling of the cell walls is the main reason for the damage.
- Increasing face sheet thickness increased flexural strength of
specimens for both face sheet materials. This increase was more
apparent in specimens of CFRP.
- While performing fatigue tests, the applied load was determined by
using the static damage load of the specimen. This restricted the
effect of parameters used in the study on fatigue behavior.
Application of the same amount of load to all specimens will clarify
the effects of these parameters on fatigue behavior.
- Increasing the core height was found to be the parameter that
increased fatigue strength of specimens the most, similar to static
loading.
- In fatigue tests performed by three-point bending tests, when the
loading ratio decreased, the fatigue lives of undamaged and damaged
specimens converged.
- The damping ratio – related to the energy absorbed by specimens
during fatigue tests and to rigidity – increased with increasing
impact energy. For undamaged and damaged specimens, the damping ratio
approached a steady-state and continued its horizontal trend; it
decreased when approaching the damage cycle and became a minimum after
permanent damage of the specimen.
- For all cycle numbers, the highest damping ratios were observed in
specimens with the aluminum face sheet.
- While normalized fatigue cycle approaching the 1, stiffness decreases
and dramatical stiffness reduction observed at the end of lifetime for
all samples.