Abstract: Propagation characteristics of longitudinal modes of ultrasonic guided waves are researched for the defect detection on helical bellows. The finite element models of helical bellows are created using commercial package Abaqus firstly and the results of numerical simulation with a circumferential crack have been calculated. Furthermore experimental research is developed using electromagnetic acoustic transducer. The sinusoidal tone burst modulated by a Hanning window with 20 cycles is used for exciting ultrasonic longitudinal guided wave mode L(0, 2) at 240 kHz in helical bellows to detect artificial defects. Single transducer is applied for the excitation and reception of L(0, 2) modes simultaneously. The crack in helical bellows can be identified and Uncertainty of measurement result has been calculated. The finite element analysis and experimental results show that it is feasible and effective to detect defects in helical bellows based on ultrasonic guided wave technology.

Key words: Guided waves, Helical bellows, Numerical simulation, Pulse echo