Study of In-Plane Mechanical Behavior of Bio-Inspired Hierarchical Honeycombs

Abstract

The study of in-plane mechanical behavior of hierarchical architected structures inspired by nature is of utmost interest because of the growing needs of lightweight high performance materials demonstrating better energy absorption and load bearing ability, combined with significant shape-memory effects. Even though plenitude of studies can be found analyzing the mechanical response of honeycombs with different hierarchical orders, yet there are very few studies which compare the mechanical properties of different structural topologies with each having different modes of hierarchy. This study seeks to get an insight of how the mechanical behaviors of hierarchical structures can be tailored both by inclusion of hierarchies, and by varying the hierarchical organizations. The hierarchies are introduced in the cell walls of the unit cells taking 2 different unit cell topologies – square and kagome, with varying relative densities. Unit cells of each topology are designed with 3 different hierarchical configurations – primitive (base), nested, and fractal. The unit cells and the structures are additively manufactured by stereolithography using rigid resin, and are subjected to uniaxial compression for in-plane mechanical characterization. Besides, computational analyses are made to determine the in-plane homogenized mechanical

properties of the unit cells, applying periodic boundary conditions. Both the computational and the experimental studies show that the stiffness, and the energy absorption properties of the structures vary not only according to the topology and the hierarchical order of the unit cells, but also according to the hierarchical organization – for a particular relative density. Hence, the study shows that under a specific order of hierarchy and relative density, the mechanical properties of these cellular structures can be tailored by varying both the topology and the hierarchical organization to meet a specific requirement.