How to Reach 100% Inspection Coverage of Aeroengine Fan Blades with a High Probability of Detection

Abstract

In aviation, quality is paramount to determine an aircraft’s airworthiness and keep personnel and passengers safe. Non-destructive testing (NDT) methods are largely used throughout an aircraft’s lifetime, including raw material selection, manufacturing, assembly, and in-service maintenance. As a key component of aircraft, engines are governed under strictly scheduled maintenance programs where they are dismantled and thoroughly inspected. Part of this global inspection concerns the individual verification of fan blades to assess the absence of flaws, such as surface cracks. Due to the complex geometry of fan blades, established methods such as penetrant testing (PT) and magnetic particle inspection (MPI) have been successfully used in past decades to detect surface-breaking flaws in fan blades. However, these techniques are complex to deploy and do not permit results traceability. As an alternative, eddy current (EC) technologies proved to be a good candidate to discriminate flaws as small as 1 mm long. Combining both conventional and eddy current array technology provides valuable information on the integrity of the component. Powered with the development of dedicated signal processing methods, the proposed solution helped to increase signal-tonoise ratio, avoiding any false calls. Once this was achieved, a careful study of the probe’s deployment and compliance with the various changes of geometries—from the blade’s surface to its edges and root, helped ensure optimal crack detection. Finally, recent advances in robotics enabled an automated inspection strategy to perform 100% coverage with high reproducibility and repeatability. This greatly improved the probability of detection of sub-millimeter surface-breaking cracks. This paper describes the study performed to assess the capability of eddy current solutions (conventional and advanced) to replace traditional methods of inspecting titanium fan blades. It also shows how dedicated signal processing enables increased probability of detection. The proposed approach to provide full coverage of the complex geometry and the associated developments are detailed. Finally, the paper presents an integration of the complete inspection technique in an automated system.