(253ca) Forming Auxetic Materials from Amorphous Networks

Auxetic materials, those with negative Poissonâ??s ratios, are a promising candidate for impact control and mitigation. Recent work has shown that in amorphous solids, the contribution of any one bond or interaction to a given global property is not correlated with its contribution to other properties. We exploit this bond-level independence to independently modify the bulk and shear moduli of large-scale amorphous networks of nodes joined by bonds, creating auxetic materials. We develop straightforward computational models which classify the usefulness of a range of real materials towards creating amorphous auxetic materials. Given an appropriate choice of real material properties, simulated materials can be modified to be either fully incompressible or fully auxetic using a variety of boundary conditions. Such techniques can be applied to both two and three dimensional materials. Materials designed in simulation are created using 3D printing, and show excellent agreement with our models. Using both simulation and experiment, we probe the impact absorption properties of these materials.