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)
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