Stability of elastic material with negative stiffness and negative Poisson's ratio

Abstract

AbstractMost elastic systems exhibit a positive stiffness: a deformed object experiences a force in the same direction as the deformation. An object with negative stiffness is possible, but it is unstable. Such an object can be stabilized by a hard constraint on the entire surface. In the Editor's Choice by Shang Xinchun and Roderic S. Lakes, it is shown that a partial constraint suffices to stabilize a body with negative stiffness [1].The diagram on the cover of this issue shows regions of stability in a map of bulk modulus (resistance to volume change) and shear modulus (resistance to shape change). A region corresponding to negative Poisson's ratio is also shown. Negative Poisson's ratio materials were developed by one of the authors (Lakes). Stability of solids with negative moduli is of interest in the context of composites. In the authors' laboratory, composites have been made with inclusions of negative modulus. These composites exhibit extreme values of viscoelastic damping and of stiffness.Corresponding author Roderic S. Lakes is Professor of Engineering Physics at the University of Wisconsin. His research focus is the creation and characterization of materials with extreme and unusual physical properties. His group is developing materials with reversed properties, including negative Poisson's ratio, negative stiffness, and negative thermal expansion.