Cross-sparse representation based on dispersion dictionary for ultrasonic guided wave to messenger cable damage detection in cladding zone

The damage detection of messenger cable is an important guarantee to ensure the safety of electrified railways. The traditional nondestructive testing methods have difficulty in accurately detecting the damage of messenger cable in cladding zone. In this paper, a novel cross-sparse representation (CSR) method based on dispersion dictionary for ultrasonic guided wave (UGW) is proposed for the outer stranded wire of messenger cable in cladding zone. Firstly, the dispersion curves of UGW in multilayer spiral structure are solved by semi-analytical finite element method, to select an appropriate excitation signal. Secondly, the stationary phase approximation method is used to construct dispersion dictionary according to the dispersion curve which can characterize the modes and propagation distance of UGWs, and the CSR is proposed to separate and identify the damage signal. Thirdly, the simulation models of different damages in the outer stranded wire of messenger cable in the cladding zone are established to analyze the correlation between the damage rate and damage index in the cross-sections. Finally, the damage recognition effect based on CSR is analyzed and compared by experiments. The experimental results show that compared with the sparse representation (SR) method using traditional dictionary, the proposed method can improve the average accuracy of damage signal recognition from about 20% to 99.4% within a wide threshold range.