Abstract: The relationship between the wave-packet duration of ultrasonic longitudinal guided waves with lower order and the inner-radius-thickness ratio(IRTR) of free pipes was analyzed at various propagation distances, various frequency-thickness products and various cycle numbers of the input pulse signal. The results show that when IRTR is smaller, the change of IRTR has a greater influence on the wave-packet duration of guided waves; but with the increase of IRTR, the influence of IRTR on guided waves will be reduced. The influence of IRTR on guided waves will also be reduced with the increase of the order of guided waves. On the other hand, for pipes of different IRTR, one should select different modes, and choose different cycle numbers and different frequency-thickness products.

Key words: wave-packet duration, pipes, ultrasonic guided waves, inner-radius-thickness ratio, non-destructive testing