Free vibration response of sandwich composites with auxetic chiral core

The aim of this study was to investigate the influence of auxetic core structure pattern and boundary conditions on the vibration behavior of square flat sandwich panels. The sandwich composite panels consist of three layers, with the top and bottom skins of orthotropic E-glass/epoxy laminates and the central auxetic core layer of chiral structures with negative Poisson's ratio using the isotropic PLA material. The core structures consist of tetrachiral, anti-tetrachiral, and hexachiral auxetic cells with constant ligament length and node diameter. The face sheets were produced by the hand-layup method and a three-dimensional printing technique was utilized to create auxetic cores. In order to find natural frequencies and the mode shapes of sandwich panels with different auxetic cores, the numerical analyses were performed for the sandwich panels under free-free (F–F), simply supported (S–S) and clamped (C–C) boundary conditions using ANSYS software. Additionally, the finite element analysis results were compared with vibration test results that were conducted on sandwich panels under only the freely boundary condition to confirm the accuracy and efficiency of the finite element analysis. The results obtained from the simulation suggest that the auxetic chiral cores have promising properties for dynamic performance. In particular, hexachiral cores were shown to effectively increase the natural frequency compared to anti-tetrachiral and tetrachiral cores. Although the use of auxetic core structure in sandwich structures significantly increases the natural frequency, the natural frequencies of sandwich panels with different core patterns are close to each other.