Defect sensitivity in lamb wave testing of thin-walled tubing

Ultrasonic testing of fuel cladding usually involves the use of moderate- frequency search units. The relatively thin wall, small radius of curvature, wave length, and physical size of sound beam are considerations in describing the predominant type of ultrasonic wave resulting and the nature of the energy reflection process at a defect. Shear and Lamb waves are generally assumed to be the main wave forms pertinent to fuel clad testing. The observed waves are discussed with regard to their nature and ability to permit excitation over wide incident angle ranges and to such properties as attenuation and sensitivity to some types of defects. General Lamb wave theory is not sufficient to explain the behavior of the waves. A new model describing a surface wave or possibly a degenerated Lamb wave is outlined and discussed with reports of laboratory measurements as well as observations from practical testing using both echo technique and through-transmission.