Figure 4. Stress vs. Cycles to failure graphs for the materials
used
Results
This study experimentally investigated the effect of preliminary impact
damage on the fatigue behaviors of honeycomb sandwich composites.
Preliminary impact damage was formed at impact energies of 5 Joules and
10 Joules as a result of low velocity impact tests. The effects of the
preliminary impact damage on the strength and fatigue lives of specimens
were investigated by bending tests. The results obtained are given
below.
4.1. Flexural Tests
Figure 5 shows the images of specimens – with aluminum and CFRP face
sheet materials – obtained after three-point bending tests for
different face sheet thicknesses. Examining the images, in the model
with an aluminum face sheet of 0.5 mm thickness, face wrinkling damage
was observed at the first contact point of the cylinder used to apply
the load. This damage was seen to be less in the model with a 1 mm face
sheet thickness, while it was not seen in the specimen with a 1.5 mm
face sheet thickness.
For specimens with a 0.5 mm thick CFRP face sheet, local crushing was
dominant in the honeycomb core to which the load was applied. The amount
of deflection increased with increasing face sheet thickness and the
highest flexural damage was observed in the model with a face sheet
thickness of 1.5 mm (Figure 5).