Abstract |

**On the Origin of Dynamic Elastic
Nonlinear Behavior in Solids**

*D.Pasqualini, P.A.Johnson, J.A.TenCate,
T.W.Darling (Los Alamos National Laboratory, Los Alamos, NM, USA)*

*e-mail:
dondy@lanl.gov*

It
has recently become clear that a large category of materials exhibit an
identical, nonlinear elastic signature [R.A.Guyer and P.A.Johnson, Physics
Today Apr. 1999]. These materials (rocks, sand, cement, concrete and ceramics)
have been termed nonlinear mesoscopic elastic (NME) materials, in contrast to
the well-known nonlinear atomic elastic (AEE) materials . The difference
between these two categories of materials is both in intensity and origin of
their nonlinear responses. The atomic elasticity of AEE arises from
atomic-level forces between atoms and molecules and they can be described by
the traditional theory of elasticity. In contrast, the NME materials contain
small soft features called "bond system" within a hard matrix,
producing very large nonlinear response. Hysteresis, wave distortion, harmonics
and in particular relaxation (slow dynamics effects) are important
manifestations of this nonlinear behavior. It is also observed that a damaged
AEE material responds like a NME material. When damaged, engine blocks,
bearings, sophisticated composites and other materials display nonlinear
mesoscopic elasticity that appears to be much like that in rock. To present the
state of the art in understanding of the origin of this behavior is the
intention of this presentation. An overview of the different modeling and
experimental approaches having been using to explore these phenomena will be
discussed.

Section
: 3