Abstract: Excitation and reception methods of the longitudinal guided wave modes in steel strands based on magnetostrictive effect are analyzed theoretically and verified in the experiment. Propagation characteristics of longitudinal modes in a 17.80 mm nominal diameter steel strand are firstly investigated. L(0,1) mode at 160 kHz in one of helical wires is optimized for health inspection of the steel strand. Based on propagation characteristics of this mode and peripheral winding surface of steel strands, a kind of special magnetostrictive transducer is developed for ultrasonic guided wave inspection of seven-wire steel strands. The transducer mainly consists of axisymmetric three permanent bias magnetic circuits and a three-section spiral tube with reverse normal winding directions. These axisymmetric circuits are used for producing bias magnetic field with suitable and uniform strength, and the special clamp groups are designed for reducing air reluctance caused by irregular contour of steel strands. Effective axial width of each section of spiral tube equals to half wavelength of L(0,1) mode at 160 kHz. By using these developed magnetostrictive transducers,guided wave excitation and reception are achieved in a 1 180 mm long free steel strand. Experimental results show that chosen L(0,1) mode can be excited and received by using developed magnetostrictive transducers. These transducers will provide the experimental basis for ultrasonic guided wave inspection of steel strands based on magnetostrictive effect.

Key words: Magnetostrictive effect, Mode, Steel strand, Transducer, Ultrasonic guided waves