Guided circumferential waves in annular structures

Radial fatigue cracks are found in many annular structures, where these flaws can grow from interfaces between shafts or from the inner surface of a hollow cylinder, and cause catastrophic failure. These parts are usually inspected visually, but this technique is time consuming and inaccurate.; In this research, a guided wave technique is developed and used to detect radial cracks in annular structures such as the rotor hub and its pitch-shaft assembly of the H-46 helicopter. Both theoretical and experimental investigations are conducted to develop a framework for such a guided wave technique. The objectives of the proposed research are to further the fundamental understanding of the mechanics of guided waves in cylindrical structures, to perform parametric studies to model the generation and propagation of such waves so that their characteristics may be optimized for crack detection, and to provide a new methodology to locate and size existing cracks.; The key contributions of this research include: (1) computational modeling of the propagation of guided waves in cylindrical structures of various geometries, in both steady-state and transient conditions, with experimental validation; (2) Finite Element (optimization) parametric studies to illustrate the impact of various experimental variables on the propagation of guided waves; (3) two energy-based methods for sizing cracks in plates and cylinders; (4) a time-frequency signal processing tool, derived from speech recognition concepts, for localizing cracks in plates and cylinders.; This NDE technique can detect cracks as small as 100 mum, provides a wave propagation visualization tool, and is experimentally verified.