A review of noise control methods for composite structures.

Abstract

Composite materials and structures offer great promise to all air vehicles and are being increasingly considered for lightweight advanced applications. However, composite structures are efficient radiators of noise mainly due to excitation and propagation of supersonic bending and/or shear waves in the structures. Composite skin-stringer structures mostly support supersonic flexural or bending waves propagating in the laminated structure whereas noise radiation by sandwich structures is dominated by supersonic shear waves in the core. The vibro-acoustic behavior of sandwich composites has been studied by several investigators. Wave number diagrams have been useful in identifying supersonic flexural and shear waves in composite structures. It has been shown that the radiating wave number components increase with increasing plate stiffness, causing increased sound radiation. Although design criteria for sandwich composites in terms of sub-sonic core wave speeds have been evolved, skin-stringer composite structures must use added noise control treatments. Noise control of composite structures, thus, still presents a significant technical challenge as the main advantages afforded by these structures, such as low weight and high strength, must not be compromised by added treatments. This paper presents a review of recent advances in the noise control techniques for composite structures.