Optimal design of a novel graded auxetic honeycomb core for sandwich beams under bending using digital image correlation (DIC)

Abstract

The present paper proposed an auxetic honeycomb for sandwich structure with a novel graded design. The auxetic graded design is achieved by a variation of honeycomb cell angle through the core thickness. This variation affects the other geometric parameters and the mechanical properties. The enhanced specific bending properties of the sandwich structure are obtained by using Taguchi design of experiments (DOEs) by optimizing the cell wall thickness, cell aspect ratio, and cell angle gradation. The specimens of the DOEs are fabricated using fused deposition modeling (FDM) 3D printer. The strain fields in the core and the damage evolution under real-time flexural loading conditions are assessed by performing digital image correlation (DIC) analysis. The experimental and DIC analysis results are validated by the three-dimensional finite element analysis with consideration of elastoplastic behavior and crack growth possibility. The results indicate that the reduction of the cell wall thickness to length ratio increases the bending failure stress and specific absorbed energy by 35% and 45.8%, respectively, and the optimum cell angle gradation improves the flexural modulus to density ratio with an increase of 18.9%.