Indentation resistance of the re-entrant hexagonal honeycombs with negative poisson's ratio

The influences of the cell-wall angle on the indentation resistance of the re-entrant hexagonal honeycombs with negative Poisson's ratio are studied by employing both the numerical tests and the theoretical analysis. In the numerical tests, two groups of honeycombs are investigated, i.e. the same-density group and the same-cell-wall group. It is shown that the honeycomb's indentation resistance increases with the cell-wall angle in the same-density group, while the cell-wall angle plays a minor role in the same-cell-wall group. The theoretical analysis is employed to explain the phenomena. The effect of the negative Poison's ratio is calculated to increase with the cell-wall angle. The average stress of the re-entrant honeycomb during compression is deduced as a function of the cell-wall angle and the cell-wall size or the honeycomb's relative density. The analytical results are consistent with the numerical tests and give an explanation for the phenomena in tests.