Andrew N. Norris
Dept. of Mech. Eng., Rutgers Univ., Piscataway, NJ 08855
Gerry V. Storch
Exxon Res. and Eng., Annandale, NJ 08801
Experimental results will be presented showing that it is possible to reduce reflections at the edges of plates and bars by using a graded impedance interface. A perfect impedance mismatch at the boundaries results in 100% reflection of waves, hence the motivation for using a graded impedance interface. An aluminum bar, a lucite bar (2 ftx1 in.x1 in.), and a viscoelastic strip (2 ftx1 in.x0.5 in.) are glued at the edges of a steel plate (2 ftx2 ftx1 in.), in order to achieve the graded impedance interface. The center point impulse excitation response is measured, and the peaks in the velocity response give a measure of the intensity of the reflected waves. A reflection coefficient R is defined based on a one-dimensional wave model. R is as low as 0.17 for the steel plate with the graded impedance interface mentioned above. Similar results are obtained for a steel bar, for which a value of R=0.31 is obtained by the same type of impedance grading. The reduction in R for both bars and plates is superior to that obtained using dry or wet sand as a vibration absorption mechanism.