Consideration of Wedge Material for Contact-Type Line-Focus Ultrasonic Probe(<Special Issue>M & M 2009 Conference)

Ultrasonic flaw sizing is an important issue for insuring structural reliability and remaining life prediction of industrial plants. The Time-of-Flight Diffraction (TOFD) method is one of the most effective tools for sizing flaws. However, due to the difference of the acoustic impedance between the wedge and specimen, unexpected shear vertical and Rayleigh wave are generated at the interface by mode conversion. These waves occasionally disturbs the received TOFD signal hence it is important to reduce the mode conversion waves. In this study, a new Line-Focus longitudinal wave probe is developed to reduce mode conversion waves. This probe is composed of a cylindrical stainless steel wedge and piezoelectric transducer adhered to the cylindrical surface of the wedge from 20 to 70 degree. This probe can excite the longitudinal wave which is incident on the specimen surface at almost all angles from 20 t0 70 degree simultaneously. In addition, if this probe is applied to stainless steel specimen, the amplitude of mode converted waves are expected to become smaller because the acoustic impedances of wedge and specimen are the same. In this research, for the basic performance evaluation, the directivity of the new Line-Focus longitudinal wave probe is evaluated with the examination using half-cylindrical steel specimen and the two dimensional numerical simulations.