Filtering of NDT signals obtained from wrapped steel cables

摘要

The main cables of suspension bridges are often wrapped with a steel wire, in order to compact the cable and hold it in shape. If a non-destructive evaluation by means of magnetic methods is performed on such a cable, disturbances due to the wrapping can be expected in the measured signal. In the presented work, these disturbances shall be quantified and compared to the flaw signals. Different approaches for the separation of the disturbance and the flaw signal are discussed. Additionally, the possibility to detect wire breaks and corrosion within an unwrapped steel cross-section could be shown in laboratory measurements. The influence of the wrapping was investigated using finite element (FE) simulations and experimental laboratory measurements. A parameter study was performed in order to obtain data in which the components from a flaw and the wrapping can be separated. The parameters varied in this study were chosen depending on the prospect of success and the cost of the realization. Using these data sets different filtering methods, such as wavelet analysis, were implemented. A final comparison of the different methods suggests the most efficient way to assess the condition of such cable systems using magneto-inductive testing. Finally, it can be concluded that the use of FE simulation is a very useful tool for the development of new data analysis methods, even if a real set-up and data from measurements exist.