Research And Application Of Ultrasonic Waves In Multi-wire Strands

Multi-wire strands, whose basic elements are usually a straight core and a layer of helical wires,are widely used in engineering applications. As those structures are exposed to severe natural andworking conditions (acid rain, wind drag, atmospheric corrosion, vibration, fatigue, etc.), it isessential to study their reliability that concern the security of users and environment closely. Methodsbased on ultrasonic waves are gaining increasing attention in Non-destructive testing due to theirability to examine the entire structure far and efficiently. In this paper, the propagation characteristicsof ultrasonic waves in multi-wire strands are investigated via simulation and experiment, and thenthey are used to detect and locate the damages.Firstly, the influence of preload on the coupling transmissibility and attenuation of ultrasonicwaves is studied at the level of individual wire. It is found that when one of the helical wires is excited,the response of each wire tends to be identical as the preload increases, indicating that thetransmissibility between individual wires is independent on the geometric position when the preload islarge enough. In this case, the ultrasonic waves in each wire attenuate exponentially, sharing a sameattenuation rate.Secondly, as the surface of the multi-wire strand is rather complicated, conventional transducerscannot be directly used to excite and receive ultrasonic waves in the strand. A special transducer isdesigned according to the structure of the strand. Suitable excitation frequency is chosen and thelength of the transducer is optimized to excite one single ultrasonic wave mode.Finally, combining the propagation characteristic of ultrasonic waves, damages are detected bythe signal processing method based on estimate of standard deviation and the damages are locatedaccording to the signal’s arrival time extracted by Hilbert transform, proving the feasibility ofdetecting and locating damages by ultrasonic waves.