Vibroacoustic Optimization of Sandwich Structures with Auxetic Cores

This research describes the vibroacoustic behavior of sandwich structures with various core topologies. In the first part of this research a novel core topology made from 2- Dimensionally gradient auxetic hexagonal honeycombs has been proposed. The 2D gradient core enables a tailoring of localized mechanical properties of the sandwich structure in different regions of the panel. A homogenized finite element modeling is used to determine the mechanical properties of the sandwich structures. The natural frequencies and the radiated sound power level of the sandwich plate with the homogenized properties have been calculated and verified with those obtained from a exact FE model of the sandwich structure. The geometry of the 2Dimensionally gradient auxetic core has been then optimized using two different techniques in order to minimize the radiated sound power level over the frequency range of 0 to 200 Hz. The optimized design of the 2D gradient core shows a remarkable reduction of the radiated sound power level for the sandwich structure when taking into account the mass of the structures. In the second part of this study this 2D gradient core topology concept is used in a sandwich structure with anti-tetrachiral cores. The same homogenized finite element approach is used to determine the mechanical properties of the anti-tetrachiral core and a multivariable optimization procedure is applied to minimize the radiated sound power level of the sandwich structure over the frequency range of 0 to 200 Hz. In this part a mass constrained optimization procedure is conducted. The maximum increase in the total mass is considered to be 10% of the mass of the base line configuration. The optimized structure shows a significant reduction in the radiated sound power level accompanied by an increase in the natural frequencies of the sandwich structure.This study provides new insights about the vibroacoustic behavior of auxetic sandwich structures with complex core geometries. Keywords: auxetic, hexagonal, chiral, anti-tetrachiral, 2D gradient, sandwich structure, vibroacoustic, optimization, genetic algorithm, MMA