Acoustic monitoring of beams by time-frequency analysis.

Abstract

Acoustic vibrations can be used to monitor the structural integrity of metallic beams. A current technique involves impacting a beam with a hammer and analyzing the induced vibrations. However, the generated vibrations exhibit transient and nonstationary characteristics such as rapid decay of amplitude and time-dependent frequency content. This observation limits the use of classical spectral analysis which requires stationarity. Time-frequency representations, such as the Wigner distribution, provide a more general framework to analyze transient and nonstationary signals. Actual beam vibrations, analyzed with time-frequency representations, will be presented. In particular, it will be shown that this analysis enhances the appearance and disappearance with time of specific frequency components as well as changes of the resonant frequencies. These observations can ultimately be used as discriminative features in a pattern recognition scheme classifying good and cracked beams. [Work supported by NSF Grant No. MSS-9024224.]