Measurement of the elastic modulus of homogeneous materials by a bending wave speed method

Elastic modulus is one of the most important mechanical properties of homogeneous materials. It describes the dynamic behaviour of elastic and viscoelastic materials, strongly affecting both panel modes and coincidence frequencies, so is an important quantity to consider in noise and vibration control. A method to obtain the elastic modulus of materials is proposed herein, based on the measurement of the surface velocity field occurring due to the propagation of bending waves through a panel. A 2D spatial Fourier transform applied to the measured velocity field allowed evaluation of the wavevectors of the free bending waves propagating in the panel. By averaging over wave direction, the overall amplitude distribution versus wavenumber can be found, and from this the dominant wavenumber obtained. From the latter it is straightforward to calculate the flexural wave speed, which can, via classical plate theory, be related to the static elastic modulus value of the material. A preliminary experimental test-rig was based on laser Doppler vibrometry measurements in order to assess the surface velocity of a freely suspended sample, acoustically excited by a broadband signal. The experimental results show a reasonable agreement to the manufacturer’s technical data and to the outcomes of related numerical simulations, although some issues require further research.