Smart and Robust Composite Scarf Repair using Visual Assistance, crack arresting and crack detection Systems

Kurzfassung

The certification of safety-critical bonded repairs in composite aircraft structures remains challenging, particularly because current non-destructive inspection methods cannot directly determine the in-situ strength of an adhesive joint. This work presents an integrated approach combining quality-controlled scarf manufacturing with structural health monitoring and inherent crack-arrest capability.

A visual assistance system developed at the German Aerospace Center (DLR) uses 3D scanning and projection technology to guide technicians during scarf grinding, patch manufacturing and placement. Deviations between the actual and target geometries are continuously evaluated and projected onto the structure, enabling controlled material removal and digital documentation of the final repair geometry.

To increase the robustness and inspectability of the bonded repair, a continuously measuring fibre-optic sensor (FOS) is integrated for crack detection, providing a spatial resolution of 0.65 mm. In parallel, a surface-toughening concept based on locally introduced thermoplastic polyurethane (TPU) is used to reliably arrest propagating cracks within the bonded interface.

Both concepts were experimentally investigated from coupon to element level under quasi-static and cyclic loading and subsequently combined in an industry-oriented demonstrator within the European GENEX project. The resulting smart and robust repair concept combines guided manufacturing, quality assurance, damage detection and crack arrest, providing a promising approach towards more reliable and certifiable bonded composite repairs.