Low-velocity impact response of sandwich panels with hierarchical honeycomb and graded hierarchical honeycomb cores: A numerical approach

This study applied hierarchical honeycomb and graded hierarchical honeycomb cores to sandwich structures for creating two new types of lightweight and high impact-resistant honeycomb sandwich panels. The finite element model validated by the experiment was established to investigate the impact responses of the hierarchical and graded hierarchical honeycomb sandwich panels under low-velocity impact energies. Theoretical formulas based on the energy-balance model were established to predict the total energy absorption, maximum impact force and residual lower facesheet deflection of both the conventional (Type 1 structure) and hierarchical (Type 2 structure) honeycomb sandwich structures. A polynomial model was used to establish the regression equations for the structural stiffness, upper facesheet indentation depth, and residual lower facesheet deflection of the sandwich structures with double-layer graded hierarchical honeycomb cores (Type 3 structure). The improved Non-dominated Sorting Genetic (NSGA-II) algorithm was employed to perform a multi-objective optimization design on the impact responses of Type 3 structures. The results showed that both the hierarchical and graded hierarchical honeycomb cores can improve the stiffness and impact resistance of sandwich structures when the density of sandwich structures was same. However, under an impact energy of 100J, applying the hierarchical honeycomb core to the Type 2 structure increased the deflection of the lower facesheet. Compared to the Type 1 structure, the optimized Type 3 structure exhibited the highest structural stiffness and both the smallest upper facesheet indentation depth and the smallest residual lower facesheet deflection under an impact energy of 100J, with improvements of 39%, 15%, and 33%, respectively. Moreover, the low-velocity impact responses of Type 2 and Type 3 structures were influenced by the structural organization parameter and the gradient rate. The promising results of the present study may be expected to provide some insights for the design of more efficient crashworthy structures.