The effects of structural variations on the health monitoring of composite structures

Composite repairs have been demonstrated to be an effective and efficient method of repairing or reinforcing aircraft structures. However, the implementation of this repair scheme gives rise to the difficulty in monitoring of the growth of the defect or crack beneath. In-situ monitoring methodology can be developed to monitor the fatigue crack development after the implementation of this repair on the structure. This paper presents a set of numerical results on the use of Lamb waves for the monitoring of crack growth in the lower wing skin adhesively bonded with a composite repair patch. These results demonstrate that the monitoring of defect growth beneath a repair patch can be made more challenging if severe geometry changes occurs in the vicinity of the defect and the multi-layered construction (with aluminum, adhesive and boron/epoxy) of the repaired structure.