Composite Materials with Viscoelastic Stiffness Greater Than Diamond
T. Jaglinski,1
D. Kochmann,2
D. Stone,3
R. S. Lakes4*
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.
2 Institute of Mechanics, Ruhr-University Bochum, 44780 Bochum, Germany.
3 Department of Materials Science, University of Wisconsin–Madison, 541 Engineering Research Building, 1500 Engineering Drive, Madison, WI 53706–1687, USA.
4 Department of Engineering Physics, University of Wisconsin–Madison, 541 Engineering Research Building, 1500 Engineering Drive, Madison, WI 53706–1687, USA.
* To whom correspondence should be addressed. E-mail: lakes{at}engr.wisc.edu
