ATTENUATION OF WAVES IN PLATES AND BARS USING A GRADED IMPEDANCE INTERFACE AT EDGES

Abstract A new method is proposed for attenuating structural wave reflections at the edges of plates and bars by using a graded impedance interface. Experimental data show that as much as 60--80 % damping of energy in a 1″ thick steel plate is achieved for frequencies from 2−10 kHz, using this approach. The measurements also indicate a trend towards greater damping for higher frequencies. The results observed in the experiments are explained using an S-matrix formulation based on Mindlin's theory for flexural waves. The classical, or Kirchhoff, flexural theory does not predict the observed levels of damping, indicating that shear effects are important in this attenuation mechanism. Numerical simulations indicate that the observed lower reflectively is caused by energy dissipation within the composite material at the free end, coupled with relatively large amplitude vibrations caused by the impedance gradation.