*3.3. Influence of Capillary Shape on the Crack Growth Life*

The crack propagation curves obtained for a part-through crack are shown in Figure 11. It can be clearly seen that varying the aspect ratio of the capillary actually has a negligible effect, as the impact on the crack propagation life remains below 2.5% variation (see Table 6). Increasing the aspect ratio of the capillary implies that the local reduction in area felt by the crack is less important than for circular capillaries. Crack propagation speeds in the neighborhood of the capillary are hence lower for elliptical capillaries. However, due to the vertical extension (along the *y*-axis) of the elliptical capillary, the time frame during which the crack propagates in a reduced available sectional area is also longer. This counterbalances the positive effect of lower propagation speeds, hence explaining why small difference in crack propagation life is obtained.


**Table 6.** Fatigue crack growth lives (*Nf* ), variations with respect to the circular capillary case (Δ*circular*) and cycles to detection (*Nd*) as a function of capillary aspect ratio, in the case of part-through crack.

**Figure 11.** Fatigue crack growth curves for various capillary aspect ratio and in the case of part-through crack.
