Optimization of Energy Absorption Performance of Polymer Honeycombs by Density Gradation

Density gradation has been analytically and experimentally proven to enhance the load-bearing and energy absorption efficiency of cellular solids. This paper focuses on the analytical optimization (by virtual experiments) of polymeric honeycomb structures made from thermoplastic polyurethane to achieve density-graded structures with combined desired mechanical properties. The global stress-strain curves of single-density honeycomb structures are used as input to an analytical model that enables the characterization of the constitutive response of density-graded hexagonal honeycombs with discrete and continuous gradations and for various gradients. The stress-strain outputs are used to calculate the specific energy absorption, efficiency, and ideality metrics for all density-graded structures. The analytical results are shown to be in good agreement with previous experimental measurements. Our findings suggest that the choice of an optimal gradient depends on the specific application and design criteria. For example, graded structures wherein low density layers are dominant are shown to outperform high density uniform honeycombs in terms of specific energy absorption capacity while possessing higher strength compared with low density uniform structures.