High Damping Composite Materials: Effect of Structural Hierarchy

A combination of stiffness and loss (the product Etan ) is desirable in damping layer and structural damping applications. Composite materials of structure which gives rise to Reuss or Hashin–Shtrikman lower bound behavior can give rise to such properties. Hierarchical particulate morphologies attain the Hashin– Shtrikman curve. We show that hierarchical composites give rise to complex Poisson’s ratios which, however, have minimal effect on the stiffness-map. We show that structural hierarchy is useful in viscoelastic composites in that it enables the attainment of high concentrations of spherical inclusions, and that it facilitates the attainment of both stiffness and damping. A damping layer upon a substrate is considered as the top level of the structural hierarchy. We demonstrate that if the layer itself is a relatively stiff composite, the penalty usually associated with such a geometry for compliant layers is ameliorated.