A refined model for the effective in-plane elastic moduli of hexagonal honeycombs

Honeycombs are discrete structures that can be placed as cores between composite facesheets to form sandwich structures. The modeling of the effective properties of these honeycomb cores is of key importance to predict the overall mechanical response of the sandwich structures. Existing models that predict these properties usually assume that these honeycombs consist of straight walls, but close examination of commercial hexagonal honeycombs shows that the walls are instead curved in the vicinity of the intersection points of the hexagon due to corrugation or expansion during manufacturing. A refined model that predicts the effective honeycomb properties is thus needed to take into consideration such curvature. In particular, the in-plane elastic moduli were studied by analytical and numerical means and correlated with experimental results for aluminum hexagonal or regular honeycombs. These elastic moduli are predicted as a function of radius of curvature at the intersection points, relative density as well as cell dimensions, considering the effect of bending, shear and axial deformations in both in-plane honeycomb directions. This refined model better predicts the effective moduli of honeycombs with low relative densities and represents also a general solution that can be reduced to predict the effective mechanical properties of regular honeycombs with straight walls.