Ultrasonic NDE of Integrally Fabricated Turbine Rotors

Abstract

A new challenge to ultrasonic inspection techniques is the NDE of integrally fabricated turbine rotors, where the turbine blades are either bonded to the disk in the manufacturing process or during rotor repair. Although reliable detection of gross defects, such as significant disbanded areas, is certainly essential in bond NDE, this project is primarily concerned with the detection and characterization of overall bond quality from a microstructure perspective. Thus, recent efforts have been directed toward seeking various ultrasonic inspection techniques which show reliable and measurable correlation to near-bond microstructure variations and which are implementable as practical inspection configurations. Experiments have been performed both on bonded specimens from two major jet engine manufacturers [1,2] and on a simulated bonded blade containing seeded defects in the bond plane [1]. Inspection modes which showed the best promise of correlation to bond quality were leaky Rayleigh waves, critical angle longitudinal waves, and longitudinal wave inspection near grazing incidence to the bond plane. These methods also are, at least in principle, implementable as practical techniques since they only require access to a single side of the blade. A second area of effort concerned application of models of imperfect interfaces [3] to the inference of bond microstructure parameters from ultrasonic scan data. Preliminary comparisons to experimental data were qualitatively favorable, but interpretation of model parameters in terms of the bond microstructure has not yet been possible. Results of the experimental tests will be presented along with the preliminary model comparisons. Analysis of the results will also concern selection of candidate techniques for implementation in the second phase of this project.