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).