Optical Damage Sensors for Automated On-Wing Engine Airfoil Inspection

ABSTRACT: Two optical methods are proposed for the detection of a range of types of damage on coated and uncoated airfoils in advanced gas turbines by means of borescope inspection of on-wing parts. The techniques are low coherence interferometry imaging of bulk TBC optical properties and luminescence piezo-spectroscopy for imaging of residual stress in the thermally grown oxide layer at the ceramic-alloy interface. The Phase II Work Plan consists of a detailed set of tasks involving design, component testing, construction, and testing of the prototype instrumentation. BENEFIT: The proposed instrumentation provides a significant advance over currently employed visual inspection of gas turbine airfoils. For instance, with thermal barrier coatings (TBCs), these techniques allow the detection and quantification of incipient spalls, delamination, and changes in TBC porosity which typically go unnoticed with visual inspection methods. The proposed methods are well suited for use with borescopes and thus provide a large potential to be developed into commercial optical diagnostics instruments for use during maintenance and inspection of on-wing airfoils in advanced gas turbines.