Under the sponsorship of the Federal Aviation Administration, an Engine Titanium Consortium (ETC) was formed in 1992, bringing together academic researchers and engine manufacturers in a joint effort to improve inspections of rotating aircraft engine components. The work described in this paper represents one chapter in that effort [1, 2]. Materials used in rotating jet engine components can be ultrasonically inspected at various stages in the manufacturing process. For example, one can inspect the cast and worked billet, the forging produced from a slice of that billet, or the final machined component itself. In any of these inspections, ultrasonic grain noise often plays an important role. This type of noise arises from the reflection of sound waves from microstructural boundaries in the metal, and it can hide the ultrasonic echo from a bona fide internal defect. Defect detection thus becomes the search for a flaw signal in the presence of noise. Strategies for designing inspections so as to boost the signal-to-noise ratio (S/N) have been studied by the ETC [3].

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