Guided wave nuances for ultrasonic nondestructive evaluation

New applications of guided waves in nondestructive evaluation are being considered on a daily basis. One decade from now, guided wave inspection programs will be commonplace. As individuals become aware of the way in which they can be used and the kinds of problems that can be tackled, their imagination and creativity can take over and propel the inspection community to new heights. Improved inspection sensitivities and cost reductions will be possible in many cases. The ability to inspect hidden areas and sections under water, coatings or insulation can become a reality, for example, with practical specially developed quick and efficient software tuning packages and instrumentation. A whole host of specially shaped and multiple element transducers will be available for a variety of different shaped and multiple layered components. Fundamentals and application logic will be outlined in this paper to foster improved understanding and excitement for the user. More specifically, recent developments in guided wave generation, reception, and mode control show that increased penetration power and sensitivity are possible. A tone burst function generator and appropriate signal processing are generally used. Variable angle beam and comb-type transducers are key to this effort. Problems in tubing, piping, hidden corrosion detection in aging aircraft, adhesive and diffusion bonding, and ice detection are discussed. Additionally, sample configurations, inspection objectives, and logic are being developed for such sample problems as defect detection and analysis in lap splice joints, tear straps, cracks in a second layer, hidden corrosion in multiple layers, cracks from rivet holes, transverse cracking in a beam, and cracks in landing gear assembly. Theoretical and experimental aspects of guided wave analysis include phase velocity, group velocity, and attenuation dispersion curves; boundary element model analysis for reflection and transmission factor analysis; use of wave structure for defect detection sensitivity; source influence on the phase velocity spectrum, and the use of angle beam and comb transducer technology. Probe design and modeling considerations are being explored. Utilization of in-plane and out-of-plane displacement patterns on the surface and longitudinal power distribution across the structural cross-section are considered for improved sensitivity, penetration power, and resolution in nondestructive evaluation. Methods of controlling the phase velocity spectrum for mode and frequency selection are available. Such features as group velocity change, mode cut-off measurements, mode conversion, amplitude ratios of transmission, and reflection factors of specific mode and frequency as input will be introduced for their ability to be used in flaw and material characterization analysis.