Ultrasonic guided waves propagation in complex structures

Multi-wire steel cables are used in many engineering infrastructures such as; bridges, ski-lifts, power, marine, civil and many other applications. They are considered to be safety critical components. The design life of these structures can be for many decades; therefore the problem of service life of the cables is very important. The location and operation of the multi-wire steel cable ensures they can be subject to variations in; temperature, pressure, pre-/post-stress and humidity. These conditions can potentially induce cracks, corrosion, delimitations and brittleness within the multi-wire steel cables. This could results in a potential source of unreliability, which could lead to failure. Therefore, there is a need for an effective examination technique that can assess the condition of the multi-wire steel cables before any malfunction takes place. In this investigation, Long Range Ultrasonic Testing (LRUT) has been selected as Non-Destructive Testing (NDT) technique to inspect multi-wire steel cables used in the marine application for defects or discontinuities. LRUT uses Ultrasonic Guided Waves (UGW) in the kilohertz range (typically between 16-300 kHz) to inspect for defects from single point of access for many meters (up to 100 m) with full volumetric coverage. The aim of this work is to demonstrate the ability of LRUT to propagate ultrasonic guided waves within the multi-wire steel cables. The work was conducted using FEA analysis along with experimental validations. The findings show that the fundamental axi-symmetric wave mode, L(0,1), can propagate within the multi-wire steel cable (up to 8 m) at an optimum frequency of 18 kHz.