In recent years, enhancements to mechanical
properties such as low velocity impact resistance and sound absorption have driven the research into fabrication and testing of auxetic materials.
Auxetic materials are those which exhibit a
negative Poisson’s ratio, n, which has been
known in highly anisotropic media such as pyrite crystals since the 1920s.
Milton, in 1992, calculated Poisson’s ratios of close to −1 in composite
materials and since then a lot of work has reflected that it is possible to
engineer a negative Poisson’s ratio in either the in-plane or through thickness
direction.
