Smart hexagonal truss systems exhibiting negative compressibility through constrained angle stretching

Abstract

Negative compressibility is the ability to expand in at least one dimension rather than shrinking upon the application of an externally applied hydrostatic pressure. It is shown that, contrary to current perception, negative linear compressibility may be obtained from re-entrant hexagonal truss systems of specific geometric features which deform through non-equal changes in the lengths of the cell walls when deforming through a constrained angle stretching rather than other modes of deformation (such as flexure or hinging, modes of deformation that also lead to auxetic behaviour in honeycombs). Negative compressibility is predicted in the vertical direction for particular re-entrant geometries of this smart hexagonal truss system when the vertical ribs are much stiffer than the inclined ribs.