Acoustics of Sandwich Structures

USC’s work on sandwich structure acoustics began in 1998 and has evolved in close collaboration with the M.C. Gill Corporation, a leading manufacturer of sandwich panels for aircraft interiors. The work has had both an applied mission and an academic focus, and presents an example of university-industry collaboration can produce mutual benefit while advancing scientific understanding. Here, we describe our research addressing three issues. (1) Loss Factors and Acoustic Absorption Loss factors were calculated for different sandwich panels to determine the effects of different skin and core materials on the acoustical properties of sandwich structures [1]. The study included various material configurations. Analysis of the results revealed (see Figure 1) that inserting a viscoelastic material in the mid-plane of the core shows the highest loss factor. Secondly, carbon fiber skins have a larger loss factor than glass fiber skins. Altering a core to have a subsonic wave speed does not show a significant increase in loss factor above the coincidence frequency. The para-aramid core outperforms the meta-aramid core for damping. The acoustic absorption for materials showed varied results. (2) Impedance Mismatch Layering gasses of differing densities on a panel leads to transmission loss due to the mismatch in impedance (see Figure 2). To further explore this, foams of different densities were layered and their collective transmission loss was compared to an equal amount of foam of a single density. Inefficient energy exchange at the interface between the foams decreases the transmitted sound. (3) Predictive Tools for Sound Transmission Numerical Modelling A modelling approach based on three-dimensional (3-D) elasticity theory is developed to study sandwich panel vibration and noise transmission [2,3]. Numerical examples showed that the prediction results from the 3-D model compare favourably with experimental data as well as with results from other high-order numerical method [4]. The 3-D model is general enough to deal with anisotropic sandwich panels as well. The formulations developed can also be used for parametric study and optimal design of sandwich panels.