Composites with Inclusions of Negative Bulk Modulus: Extreme Damping and Negative Poisson’s Ratio

The effect of a negative bulk modulus phase in elastic composites is studied. Negative bulk modulus K<0 is shown to be possible in selected unit cells. In isotropic solids, K<0 can be attained when negative Poisson’s ratio is sufficiently small, below the stability limit (for stress control) 1⁄4 1. Such materials, if used as inclusions, are predicted to be stable with respect to the band formation, even if they are large. Composites with spherical inclusions of negative bulk moduli are shown to exhibit negative Poisson’s ratio and anomalies in composite bulk modulus and Young’s modulus (and in the corresponding mechanical damping) but not in the shear modulus.