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Published February 2, 2007 | public
Journal Article

Composite Materials with Viscoelastic Stiffness Greater Than Diamond


We show that composite materials can exhibit a viscoelastic modulus (Young's modulus) that is far greater than that of either constituent. The modulus, but not the strength, of the composite was observed to be substantially greater than that of diamond. These composites contain bariumtitanate inclusions, which undergo a volume-change phase transformation if they are not constrained. In the composite, the inclusions are partially constrained by the surrounding metal matrix. The constraint stabilizes the negative bulk modulus (inverse compressibility) of the inclusions. This negative modulus arises from stored elastic energy in the inclusions, in contrast to periodic composite metamaterials that exhibit negative refraction by inertial resonant effects. Conventional composites with positive-stiffness constituents have aggregate properties bounded by a weighted average of constituent properties; their modulus cannot exceed that of the stiffest constituent.

Additional Information

© 2007 American Association for the Advancement of Science. 3 October 2006; accepted 12 December 2006. Partial support by NSF and by the NSF Materials Research Science and Engineering Center program is gratefully acknowledged. We thank W. Drugan for stimulating discussions.

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