Experimental study of mode conversion in pipes on damage detection by using longitudinal ultrasonic guided

There are three types of modes existing in pipe: longitudinal, bending and torsional modes. The time histories of guided wave propagating in hollow liquid-filled pipe can be determined from the experiment and the numerical simulation. The mode conversion phenomena can be found from these signals. Moreover, the category and generation mechanism of the mode conversion in pipes are investigated. Generally applicable theoretical formula of mode conversion is proposed for the first time. The results show that averaging signals of the sensors arranged on the surface of the pipe can suppress the bending mode. According to the dispersion curves, the suppression method of this mode is carried out by adjusting the centre frequency of the guided wave. These methods present a great effective tool for purifying detection signals and enhance the precision of the damage detection in pipes.