Investigation of Notch-Type Damage Identification by Using a Continuously Scanning Laser Doppler Vibrometer System

Abstract

This paper experimentally investigates a notch-type damage identification methodology for beams by using a continuously scanning laser Doppler vibrometer (CSLDV) system. The velocity response of a beam along a scan line under sinusoidal excitation is measured by the CSLDV system and a corresponding operating deflection shape (ODS) of the beam is obtained by the demodulation method. The ODS of the associated undamaged beam is obtained by using a polynomial with a proper order to fit the corresponding ODS from the demodulation method. The curvature of an ODS (CODS) can be calculated with a high quality due to a dense measurement grid of the ODS. A curvature damage index (CDI) is proposed to identify a notch with a length of 1 mm along a beam and a depth of 0.9 mm under different sinusoidal excitation frequencies. The CDI uses the difference between CODSs associated with ODSs that are obtained by the demodulation method and the polynomial fit. The notch is successfully identified near regions with high values of CDIs at different excitation frequencies.