Nondestructive Evaluation (NDE) Techniques for Repaired Integrally Bladed Components

Some modern gas turbine engines utilize integrally bladed rotors (IBR), sometimes called blisks (bladed disks), in the design of the fan and compressor. IBRs are unique because, during fabrication, the airfoil blades are bonded to a hub to form an integral structure, which offers performance benefits over the conventional dovetail design. There are many instances in operation when foreign object damage (FOD) to airfoils leads to the need for a partial or blend repair process. In some cases, material is added to restore lost strength and subsequently machined to reshape the airfoil; and in other cases, the integrity can be restored by simply blending out the FOD and rebalancing the component. Small damage is repaired using various patch-repair techniques. There are strict limits for which partial repair may be used, driven by the location and extent of the damage; and when the limits are exceeded, a decision must be made to condemn the component or apply a full-blade repair process. A full-blade repair requires the airfoil to be cut off and a new full-blade reattached, using a solid-state joining process. The critical nature of these components requires that the new joint of the full-blade repair be free of defects such as internal porosity, planar low-density defects, and surface nonconformities. Good joining procedures and statistical process control are effective in producing defect-free joints; however, NDE techniques must still be employed on a periodic basis to ensure that the structural integrity of the repaired joint is acceptable. The main challenges are that the inspection area has limited accessibility, the object varies in contour, and it has a changing cross section. Keystone is proposing to use pitch-catch ultrasonics and advanced eddy current NDE techniques to assure full coverage, detect the different potential defect types, and provide the required sensitivity. BENEFIT: This NDE technology will provide the Air Force and OEMs a NDE method for detecting potential anomalies on the bond joint resulting from the blade replacement repair procedure on an IBR. This proposed process will be applicable to all engines using IBRs in the engine fan and compressor. Large commercial engines are now being designed and brought to market that also have IBRs in the fan and compressor; therefore, it is anticipated the proposed technology will also have commercial engine applications in the future.