A Guided Wave Inspection Technique for Wedge Features

Numerous engineering components feature prismatic wedge-like structures that require nondestructive evaluation (NDE) in order to ensure functionality or safety. This article focuses on the inspection of the wedge-like seal fins of a jet engine drum, though the capabilities presented will be generic. It is proposed that antisymmetric flexural edge modes, feature-guided waves localized to the wedge tips, may be used for defect detection. Although analytical solutions exist that characterize the ultrasonic behavior of ideal wedges, in practice, real wedges will be irregular (containing, for example, truncated tips that are built onto an associated structure or have nonstraight edges), and therefore, generic methodologies are required to characterize wave behavior in nonideal wedges. This article uses a semianalytical finite-element (SAFE) methodology to characterize the guided waves in wedge-like features with irregular cross sections to assess their suitability for NDE inspection and compare them with edge modes in ideal wedges. The science and methodologies required in this article are necessary to select an appropriate operating frequency for the particular application at hand. In addition, this article addresses the practical challenge of excitation and detection of flexural edge modes by presenting a piezoelectric-based dry-coupled transducer system suitable for pulse-echo operation. This article, therefore, presents the scientific basis required for industrial exploitation, together with the practical tools that facilitate use. The study concludes with the experimental demonstration of the edge wave-based inspection of a seal fin, achieving a signal-to-noise ratio of 28 dB from a 0.75-mm radial tip defect.