Doubly curved truss core composite shell system for broadband diffuse acoustic insulation

The lattice sandwich structure as a new periodic sandwich model involves high stiffness and superior strength to density ratio, which can be applied for modeling lightweight systems. Compared to conventional sandwich models, it includes additional potential due to the presence of open space in the core. In other words, because of the property of 3D open-pore, the pyramid truss core can be considered as a creative model in process technology. Nevertheless, the acoustic characteristics of these types of cores can also be important in vibroacoustic performance of doubly curved sandwich systems. Accordingly, this study develops an analytical model for the first time to determine the sound transmission loss (STL) coefficient of a doubly curved sandwich shell with solid trusses considering various unit cells containing pyramidal, tetrahedral, and 3D-kagome. Modeling the system based on diffuse field, a numerical strategy is developed to obtain the limiting angle wherein no sound transmits into the system. To verify the accuracy of the offered formulation based on shear deformation shallow shell theory (SDSST), the results are validated with those experimental and numerical outcomes. It is found that modeling a shell as a truss core sandwich structure either attenuates the sound transmitted into the system or shifts the first dip point of the STL curve (curvature frequency) to lower frequencies. Numerical simulations indicate that the various terms of truss core have a different effect on STL of the modeled structure.