Transmission Loss Testing and Analysis of a Curved Sandwich Composite Panel

Abstract

*† ‡ Prediction of the transmission loss of singly curved sandwich composite panels is presented for a special class of symmetric construction. Measurements of the transmission loss for such a panel are presented and compared to the predictions. Additional results for the panel covered with acoustic absorbing foams are presented and compared to predictions. The foam addition increases the panel apparent damping, and results in a larger increase of transmission loss than can be attributable to the added mass. It is concluded that the model accurately predicts the transmission loss and other acoustic properties. It can be employed for the acoustic design of such panels. Sandwich composite panels and cylinders are extensively employed in the aerospace industry. Their applications are commonly found in aircraft, helicopters, launch vehicles, and engine cowlings. Ironically, the light weight advantage of the composite sandwich construction could lead to higher interior noise levels. The prediction of the sound transmission into such structures requires the analysis of acoustic wave propagation in curved composite sandwich panels. Moreover, control of the interior cavity noise almost always requires the introduction of acoustic treatments such as sound absorbing foam or fiberglass. This paper presents an abridged version of a wave approach analytical treatment for predicting the transmission loss of curved composite sandwich panels. Moreover, a test panel was constructed and employed in a transmission loss test for the bare panel and the panel covered with acoustic foam. Description of the test and representative results for the bare and covered panel are given. The transmission loss prediction for orthotropic and multi-layered infinite cylinders was investigated in a series of papers by Blaise et al. 1-3 They first presented a displacement field which neglected the transverse shear and rotary inertia, and followed it by a more general model referred to as the 3-D model. Modal based finite element and boundary element methods were employed for predictions of sound transmission through a curved honeycomb composite panel, and were verified in transmission loss tests.