Damage detection based-propagation of the longitudinal guided wave in a bimetal composite pipe

The aim of this paper is to investigate the damage detection based on the propagation of the guided wave in the bimetal composite pipes, which can identify damage locations in both axis-direction and circumference-direction. The feasibility of the method is showed by numerical illustration using FEM code ANSYS. Firstly, mode analysis is used to evaluate the guided wave mode and its structure, which can provide the basis of the mode selection in measurements scheme. And then, the guided wave propagation in a damaged pipe is computed by transient analysis. Sixteen nodes around the pipe wall, as probes, are used to record the guided wave signal. When Pseudo Margenau-Hill distribution (PMHD) for each signal is carried out, three types of modes could be found, which are lead mode, excited mode and lag mode in sequences. Based on the results, the arrived time of the exited mode could be used to locate damage in axis-direction, and the energy distribution around the pipe of lag mode is consistent with the damage in circumference-direction. The simulation illustrated the possibility of detecting damage location in both axis-direction and circumference-direction only depending on longitudinal ultrasonic guided waves.