Automated Eddy Current Detection of Edge Defects in a Complex Geometry Using a Magnitude Approach

Abstract

The inspection capability on turbine engine disks is important to the safety of an airplane. Eddy current inspection has been widely accepted as an effective tool in detecting small fatigue cracks on engine disks. The inspection of simple geometries such as boltholes, webs and bores in a engine disk is less complicated than those of complex geometries such as antirotation windows, scallops, dovetails and non-circular holes. One of the main difficulties in inspecting complex geometries is due to the presence of irregular edges. Raatz [1] reported the influence of edges in measuring conductivity. Williams, Tilson and Blitz [2] minimized the change of phase angle variation around an edge by the proper selection of inspection frequency and coil size. Elsberry and Bailey [3] enhanced edge defect detection by using a shielded probe to collimate the field. Hoppe and Stubbs [4], on the other hand, used the frequency content of the edge signals to discern the edge defect in antirotation windows. This frequency approach was extended to the inspection of other complex geometries such as antirotation tangs and live rims by Ko [5]. Furthermore, Ko [6] used the edge signals in scallops to position a rotational probe in a scallop prior to inspection. These techniques [4–6] are limited to partial inspection of the geometries; however, a new technique is needed if an entire inspection of a complex geometry is required. This paper discusses the use of a simple mechanical mechanism to adapt to a complex geometry, and a signal processing technique for the detection of edge defects.