Design for and Analytic Modeling of Acoustic Performance of Sandwich Structures
Sandwich panels--made up of two thin facesheets bonded to a low-density core material--are highly efficient composite structures that are widely used in aerospace applications, taking advantage of high stiffness to density ratio these structures demonstrate. The function of the core is to couple the face sheets by carrying shear loads, while the function of the face sheets is to carry tensile and compressive loads when a bending moment is applied.
Typical facesheet materials include carbon-fiber and fiberglass laminates while typical core materials include honeycombs (high-performance and high-cost) and foams (lower performance and low-cost). Unfortunately, the very properties that make these structures mechanically desirable also make sandwich structures excellent resonators, and, thus, nearly transparent to noise--particularly low-frequency noise. In many applications--such as aircraft floor panels--this noise transparency leads to uncomfortable noise levels in passenger cabins.
Traditional methods to remedy such problems typically include adding mass or bulky insulation, but are unacceptable for airborne structures and other weight-critical applications. This project aims to adapt novel self-propogating photopolymer waveguide microtruss structures for use as core material in sandwich structures. Using these microtruss structures, we can achieve more precise control of the material properties of the sandwich structure. Leveraging this material and analytic modeling techniques, this project aims to identify the optimal microtruss geometry for maximizing acoustic transmission loss through sandwich structures.
One of the underlying challenges with all of the approaches is to introduce design changes without compromising the high mechanical efficiency of the structures, and to balance the oft-times competing drivers of weight minimization with improved sound transmission loss. These activities are undertaken in collaboration with the M.C. Gill Corporation, a leading manufacturer of honeycomb sandwich panels located in El Monte, and with HRL Laboratories in Malibu.