Wisconsin Distinguished Professor,
Department of Engineering Physics, Engineering Mechanics Program, Department of Materials Science, Rheology Research Center, College of Engineering.
University of Wisconsin
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In our laboratory we synthesize and characterize materials with extreme and unusual physical properties. We have developed new materials with reversed properties, including the first 3D materials with a negative Poisson's ratio (auxetic) the first materials with arbitrarily large magnitudes of positive or negative thermal expansion. Zero thermal expansion is also attainable. We have developed the first extreme materials based on negative stiffness inclusions in composites. Recently such materials have been called metamaterials.
Materials which undergo phase transformation are of interest in the context of viscoelastic damping and of negative stiffness. Composite materials stiffer than diamond over a temperature range have been demonstrated in the lab. We investigate the freedom of natural and synthesized materials to behave in ways not anticipated in elementary continuum representations, to ameliorate stress concentrations, and to attain physical properties of much higher magnitude than anticipated from standard theories. Designed Cosserat solids have been made by 3D printing. We have made the first designed 2D chiral elastic material and the first 3D designed and 3D printed Cosserat chiral elastic material. These have been called chiral metamaterials.
We study materials with heterogeneous structure, including natural viscoelastic composites such as bone, ligament, tendon and wood, as well as synthetic composites, biomaterials, and cellular solids with structural hierarchy. Viscoelastic materials are of particular interest as high performance damping materials and as practical materials which undergo creep in industrial settings. We determine viscoelastic properties including internal friction, dependence on strain rate, and creep over eleven orders of magnitude of frequency and time, with no need for temperature shifts. We have developed materials and structures that offer extreme viscoelastic damping.
We also study practical composite materials such as dental composites for tooth restorations and aircraft composites in the context of damage resistance and damage tolerance as well as moisture ingression. Piezoelectric composites and lattices, chiral elastic lattices, as well as thermoelastic composites and lattices are presently of particular current interest. We pursue basic research as well as applied research for industry. Industrial research has included high temperature performance studies of alloys for small engines, improved shoe insoles, and advanced dampers.