Observation of Cosserat elastic effects in a tetragonal negative Poisson’s ratio lattice

Size effects are explored experimentally in a tetragonal lattice structure. Size dependence of rigidity is nonclassical elastic and is interpreted via Cosserat elasticity. The characteristic lengths are about a third the cell size. The Cosserat characteristic length for torsion is `t = 5.6 mm. The characteristic length for bending is `b = 5.4 mm. The size effect in torsion was a factor 4.5 in rigidity. The ratio of characteristic length to cell size is larger than in fully stretch dominated lattices but smaller than in bend dominated honeycombs or foams.