Attenuation characteristics of low frequency longitudinal guided waves generated by magnetostrictive transducers in bridge cables

Guided wave inspection has broad application potential in detecting defects in bridge cables. The attenuation characteristics of guided waves must be understood to quantify damage. However, owing to the mutual coupling between adjacent wires in cables, the attenuation characteristics of guided wave propagation in bridge cables are highly complex. In this work, the attenuation characteristics of low frequency longitudinal guided waves generated by magnetostrictive transducers in bridge cables were studied theoretically and experimentally. The results revealed that the energy-based model proposed herein-which considers the material damping, the energy transferred between adjacent wires and the heat energy generated by the energy transferred-performs well in predicting the energy attenuation. The frequency of the guided waves and the cable force significantly affect the model parameters. As the heat energy conversion coefficient decreases with increasing cable force, the energy of guided waves propagating at close range concordantly increases. The energy-based model for guided wave propagation in strands can be simplified as an exponential function, because energy losses and energy exchange between wires are negligible. In addition, high frequency guided waves decay faster in cables and strands. The decay rate increases more quickly with increasing frequency in the cables, as the cables have more wire contact that make high frequency guided waves decay faster. Although guided waves for 5-30 kHz decay faster in strands, the attenuation rate for guided wave propagation in cables will exceed the strands if the frequency keeps increasing.