On the mechanical properties of centro-symmetric honeycombs with T-shaped joints

Abstract

Centro-symmetric cellular honeycombs, in particular, their re-entrant version have been the subject of much research in recent years in view of their highly desirable macroscopic properties, including negative Poisson's ratio (auxetic) behavior. This work re-examines the mechanical properties of such honeycombs at the transition between the re-entrant and non re-entrant form, i.e. when the joints form a T-shaped junction, including the more general cases when the vertical ligaments have different thickness and material properties from the horizontal ligaments. It was shown through FE simulations that, contrary to current understanding, such honeycombs may deform in a manner which results in bending of the horizontal ligaments upon loading in the horizontal direction, with the result that such honeycombs may exhibit non-zero Poisson's ratio values. This effect was explained in terms of uneven stretching of the horizontal ribs upon uniaxial horizontal loading, a property which may also be employed to design honeycombs with negative Poisson's ratios.