Adhesively bonded composite repairs exhibit significant advantages in terms of mechanical efficiency compared to those effected using mechanical fasteners. However, they are at the same time extremely sensitive to process parameter variations. Small deviations against the repair specifications and subsequent flaws, could lead to disproportionally larger consequences to the final mechanical performance of the repair and to the integrity of the structure. Moreover, the inevitable differences between laboratory and repair shop conditions could induce additional “problematic” areas, which need to be reliably traced before the certification of methods and the release of individual aircraft to flight. Consequently, the existence of reliable and easy to apply NDT techniques is of capital significance to repair reliability and to flight safety. For this reason, existing NDT principles need to be adapted to the specificities of bonded composite repairs, in order to guarantee quality and durability in order to achieve flightworthiness and certification.

This proposal seeked to address this need by comparative evaluation of three different NDT techniques (namely piezoelectric ultrasound, shearography and laser ultrasound). The work assessed flaw detectability (e.g. delamination, debonding, porosity, foreign object inclusion etc.), functional reliability, repeatability of results, operational constraints, overall performance and applicability to the typical bonded composite repair cases of the aeronautical industry.

The latest developments in the NDT technology were used, in terms of methodology and equipment, which are already available among the consortium members. Moreover, as most aircraft structural repairs were not performed under ideal conditions in a laboratory, the comparative evaluation was undertaken in real-life maintenance environment, through detection and verification of flaws in actual repaired aircraft structural components.