Hydraulic oil fingerprint contamination detection for aircraft CFRP maintenance by electronic nose

The full-scale adoption of light-weighted carbon fiber reinforced plastics (CFRP) in the primary aircraft structures cannot be safely achieved without a reliable quality assurance protocol. A pre-bond cleaning state inspection of adherents surfaces by means of Non-Destructive Tests (NDTs) is absolutely necessary in order to guarantee the strength of bonded joints and so the structural aircraft integrity. Hydraulic-oil fingerprint contamination mainly occurs during aircraft maintenance operations, due to wrong handling by workers. It may severely affect the mechanical properties of bonded joints. Here, an ENEA customized electronic nose solution and a suitable measurement methodology are proposed as NDT tool for pre-bond detection of the Skydrol contamination state of the involved surfaces, at least at high concentration level. The protocol provides a reliable and efficient strategy to uplift and extend the technology readiness level (TRL) of NDTs allowing to overcome existing limitations in adhesive bonding for CFRP materials.