Study on the bending and shear properties of quasi-honeycomb sandwich structures considering the variable-density core design

Abstract

The quasi-honeycomb cell has better coplanar bearing capacity and stability in comparison with a honeycomb cell. The topology optimization can achieve the best distribution of materials within a core composed of cells. Hence, this paper makes an effort to provide a clear understanding about the enhancement effect of the core’s variable-density topology optimization on the mechanical properties of a quasi-honeycomb sandwich structure. The SR (i.e., the initials of SIMP and RAMP) interpolation function, obtained by weighting the Solid Isotropic Material with Penalization (SIMP) and Rational Approximation of Material Properties (RAMP) functions, is modified by adding the minimum elastic modulus term. The Optimal Classification (OC) algorithm is revised by adopting the volume constraint of Bi-directional Evolutionary Structural Optimization (BESO). And then taking into account the mapping between the topology elements and cells, the material distribution optimization of the quasi-honeycomb core is performed to minimize the structural compliance. The failure behavior, strength, stiffness, and energy absorption of three-dimensional (3D) printed uniform and variable-density quasi-honeycomb sandwich structures are studied by three-point bending tests, and the evolution processes and distribution laws on the displacement and strain of cores are analyzed using the 3D Digital Image Correlation (DIC) system. The comparisons between the experimental and numerical results are also carried out for the displacement and energy absorption of the sandwich structure, the bending strength of the face sheet, and the displacement and strain fields of the core. The results show that the bending strength, bending stiffness, shear strength, and energy absorption are enhanced after the variable-density topology optimization of the core, and the numerical values agree well with the experimental data. This study provides new ideas and important guidance for the variable-density design of quasi-honeycomb cores and the mechanical performance improvement of sandwich structures.