Auxetic behavior from rotating triangles

A particularly interesting set of structures which exhibit negative Poisson's ratio may be constructed using squares or equilateral triangles connected together through simple hinges. It has been proposed that these systems exhibit negative Poisson's ratios if when loaded, they deform through a mechanism where the squares or triangles remain rigid but rotate (hinge) relative to each other. Whilst a considerable amount of modeling work has been performed on the 'rotating squares' system, no attempt has been made as yet to derive the full compliance matrix S for the 'rotating triangles' structure which would give a full description of the mechanical properties of this system.