### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 4pSAb3. Attenuation of waves in plates and bars using a graded impedance
interface.

**Chandrasekar Vemula
**

**
Andrew N. Norris
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*Dept. of Mech. Eng., Rutgers Univ., Piscataway, NJ 08855
*

*
*
**George Cody
**

**
Gerry V. Storch
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**
**
*Exxon Res. and Eng., Annandale, NJ 08801
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*
A new method is proposed for attenuation of reflected energy at the edges
of plates and bars, using a graded impedance interface. A standard approach is
to embed the plate edges in sand. However, it has been verified that a graded
impedance interface at the edges is far more effective in damping the radiating
structural energy. It is well known that impedance mismatch causes complete
reflection of energy at the free edge of a plate. Hence, it seems reasonable to
expect a reduction in reflected energy when impedance is varied gradually.
Experimental results for 1-in. plates indicate that at most 30% of the energy
is damped for frequencies above 2 kHz when sand is used, whereas as much as
60%--80% of the energy is damped between 2 and 10 kHz using a graded impedance.
Experiments on bars also give similar results. A theoretical formulation for a
bar with graded impedance interface at the edges is presented, using both the
Kirchhoff and Mindlin theories. The Mindlin theory predicts the level of energy
damping that is observed in experiments, while the Kirchhoff theory predicts
much lesser energy damping. The shear effects are modeled more accurately in
the Mindlin theory and they seem to be important in this problem.