**4. Conclusions**

In the present work, the influence on fatigue life of the implementation of the effective Structural Health Monitoring (eSHM) methodology has been dealt within the context of straight lugs.

It has been shown that the inclusion of small capillaries (0.5 or 1 mm diameter) has a negligible influence on both crack initiation behavior and on fatigue crack propagation life. Conversely, large capillaries have a significant negative impact on crack growth life and crack initiation. This brings to the conclusion that proper application of the effective Structural Health Monitoring methodology requires extra engineering work at the design stage of the component, as a bad implementation can result in degraded fatigue performances. Moreover, this also sheds light on the importance of further research on hybrid manufacturing in the frame of the effective Structural Health Monitoring methodology, since that technology is deemed to enable the inclusion of capillaries that remain smooth while being very small in size.

It was also shown that the different configurations studied here present the drawback of late detection for quarter-elliptical cracks. However, thanks to the additive manufacturing process, many other configurations can be thought of to remedy this, should it be a problem for a particular application. One could think of integrating two side capillaries instead of one centered capillary, or use the weight spared with the inclusion of the capillary to increase the thickness of the lug when tolerances permit. In other words, the optimization space available in the frame of the configuration and implementation of the eSHM is very wide, and only a portion of that space has been explored here. This is especially true as additional features can be foreseen in the scope of the eSHM, such as crack localization and load monitoring. The scope of possibilities offered by the eSHM is very wide, and further research efforts should be devoted to the development of the eSHM methodology.

In this work, one important challenge to the possible practical utilization of the eSHM has been overcome. Several other hurdles exist before certification could be envisaged, but this work has demonstrated the interest and potential of equipping engineering components with the effective Structural Health Monitoring methodology. In particular, the authors intend to build a demonstrator lug equipped with this novel structural health monitoring technology, following the design recommendations of the present work.

**Author Contributions:** M.M. and E.W. performed the crack growth simulations. M.M. performed the other simulations and wrote the paper. E.W., D.D.B., M.H., J.E., Z.J. and G.A. contributed to the work through discussions and improvements to the text. P.G. supervised the works.

**Funding:** This research received no external funding.

**Acknowledgments:** The help provided and the sound advices given by the all the researchers at Cenaero is highly acknowledged.

**Conflicts of Interest:** The authors declare no conflict of interest.
