Hexagonal Honeycombs with Zero Poisson's Ratios and Enhanced Stiffness

In view of their potential applications in sandwich structures, there has been increasing interest in honeycomb networks. Several different types of honeycomb systems have been proposed each exhibiting different mechanical properties. Here we propose a new hexagonal honeycomb structure composed of two different geometrical features: a re-entrant feature which is known to generate auxetic behavior, and a non re-entrant feature found in regular hexagonal honeycombs which leads to conventional behavior. This results in a semi re-entrant honeycomb'' built of alternate conventional and auxetic layers. Finite element analysis and analytical modeling of these honeycombs show that they exhibit a zero Poisson ratio in one direction and a higher than normal Young's modulus in the orthogonal direction. We also show that by virtue of its zero Poisson's ratio, this honeycomb has a natural tendency to form cylindrical shaped curvatures, something which is very difficult to achieve with conventional or auxetic honeycombs.