Flexural wave parameter measurements of viscoelastic panels using a laser doppler correlation vibrometry

Abstract

Characterizing broadband dynamic properties of viscoelastic panel materials represents a challenging task, particularly when the frequency band of interest needs to be extended toward low frequency range. This work applies a laser Doppler vibrometer in measuring flexural wave properties of the viscoelastic panel materials. The measurement relies on a time-domain broadband correlation technique which experimentally measures impulse responses at two points radially away from a flexural wave exciter. Using reasonable sized panel samples, boundary conditions of the measurements present insignificant obstacles towards high frequency range, since a time-domain windowing facilitates extraction of direct wave components. While boundary reflections will still obscure measurement results towards low frequencies. This work examines a possible mitigation approach by rotating the sample panel, the coherence of direct wave pulses measured equidistant from the exciter and the lack thereof disturbing boundary reflections enables largely removing the undesirable reflections. In this way angular averaging significantly reduces boundary reflections. This paper discusses experimental investigations on the characterization method of flexural wave parameters including wave speed, flexural modules and loss factor.