Damage Detection Threshold of Optically-Digitized Gas-Turbine Engine Hardware

Abstract

The damage detection threshold of an optical digitization capability has been examined with respect to gasturbine engine hardware. Generally, optical inspection techniques are capable of assessing gross geometric deviations from nominal surfaces; however, the damage typical of turbine engine components – specifically of fan, compressor, and turbine blades – presents considerable challenges. To address this concern, an empirical study based on relevant airfoil inspection standards was conducted on three artifacts to assess damage detection thresholds: (1) a Titanium 6Al-4V plate with machined damage simulating various deformation criteria; (2) a compressor blade with machined damage simulating representative serviceable-limits; and (3), two fan blades with field-induced foreign object damage. Results indicate that actual damage of approximately 0.7 mil depth could be measured under stringent conditions; however, the optical system was unable to distinguish other damage features of similar depth. Furthermore, automatic detection of this damage proved difficult with the existing inspection software.