Extreme Metamaterial Lattices

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Spongy (cellular) materials are used for many purposes including seat cushions, sponges for cleaning, protective gear such as helmets and athletic pads, for flotation, and in lightweight panels in aircraft. The shape of the pores has not traditionally been subject to control. Additive manufacturing (3D printing) has recently allowed greater control over the shape of the microstructure in cellular materials. Metamaterials are materials with unusual or extreme physical properties. Among the first are the negative Poisson's ratio materials developed in our laboratory. These materials expand when stretched in contrast to rubber and common materials. Nevertheless, the freedom allowed by cellular microstructure has not been substantially exploited. To expand the freedom of design, this award supports fundamental research on the freedom associated with material heterogeneity in spongy solids. Insights from this study are intended to lead to superior materials that avoid concentration of stress around holes or cracks. New materials are to be developed with unusual and extreme deformation response to temperature and electric fields. We expect that the research to provide synergism with other branches of study including materials science, biomechanics, geomechanics and as well as nano-materials research. As with prior projects, this award will allow undergraduate students and minority students to participate in research and will facilitate incorporation of the fruits of research in the educational mission of the university. Current cellular solids, including truss lattices, have been understood using classical elasticity which is now known to be overly restrictive for such materials. A novel class of extreme lattice materials will be designed, synthesized via additive manufacturing and experimentally characterized. These heterogeneous materials will exhibit more freedom than known materials. They will be inspired by generalized continuum concepts. Materials will feature controlled nonlocality, immunity from stress concentration, control of Poisson's ratio, piezoelectricity and thermal expansion and multifunctional capacity. 3D materials will be designed for high levels of piezoelectric and thermoelastic response. Materials exhibiting new phenomena including electric field-twist coupling, squeeze-twist coupling and temperature-twist coupling will be developed. The research is intended to achieve better understanding of heterogeneous materials in the presence of stress concentrations and to provide new tools to enable the synthesis of new materials that are immune to stress concentration ands are expected to be tough. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.