Vibrations of damaged trapezoidal plates

Abstract

The modal frequencies and shapes of damaged edge‐clamped trapezoidal plates have been investigated for the first five transverse modes. Damage considered consisted of narrow, rectangular, centered slots. An impulse hammer was used to excite transverse plate vibration, and plate response was measured with a nearfield microphone. The frequency response of the plate was investigated for all combinations of three slot lengths and three slot orientations. The first five modal frequencies and shapes were estimated from ensemble‐averaged, frequency‐response functions. Observed changes in modal frequencies for the damaged plates were in good agreement with predictions of a finite element model. The results suggest that slot presence can be detected from changes in plate modal frequencies, that slot length and orientation have significant effect on the modal frequencies, that a nearfield microphone is an adequate response transducer, and that an appropriate finite element model and the frequency response measurement are of comparable sensitivity to damage. It is suggested that combining experimental modal analysis and the finite element method has significant potential for macroscopic, nondestructive evaluation.