2002 Volume 51 Issue 9 Pages 418-422
Non-destructive evaluation of a component material by an acoustic impact method was fundamentally investigated for the simplified square samples with artificial defects. Frequency spectrum, which was obtained by a fast Fourier transform of an acoustic wave form, was discussed for the evaluation of the defects on the specimen. The analyses on the frequency spectrum recognized differences in frequency and amplitude between defective and non-defective materials. The mode analyses obtained by using laser displacement rigs suggested that many peaks in the frequency spectrum were appeared by the generation of multiple vibration modes in the square specimen. It was found that the existence of small defects did not change the vibration modes but shifted the location of node and loop on one of the vibration modes against the non-defect specimen. The common frequency both of the vibration and of the sound indicated the entirely same mode number. The intensities of the two detected waves at the same location on the specimen were, however, reversed between the vibration and the sound.
