ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2pPA1. Manifestation of nonlinear elasticity in rock: Convincing evidence over large frequency and strain intervals from laboratory studies.

Paul A. Johnson

EES-4, MS D443, Los Alamos Natl. Lab., Los Alamos, NM 87545

Universite Pierre et Marie Curie, Bureau des Mecaniques, Tour 22, 4, Pl. Jussieu, 75252 Paris Cedex 05, France

Patrick N. J. Rasolofosaon

Institut Francais du Petrole, Rueil Malmaison Cedex, France

Nonlinear elastic response in rock is established as a robust and representative characteristic of rock rather than a curiosity. This behavior is illustrated from a variety of experiments conducted over many orders of magnitude in strain and frequency. The evidence leads to a pattern of unifying behavior in rock: (1) Nonlinear response in rock is enormous; (2) the response takes place over a large frequency interval (dc--10[sup 6] Hz at least); (3) the response not only occurs, as is commonly appreciated, at large strains but also at small strains where nonlinear response and the manifestations of this behavior are commonly disregarded. Nonlinear response may manifest itself in a variety of manners, including a nonlinear stress-strain relation (hysteretic/discrete memory), nonlinear dissipation, harmonic generation, and resonant peak shift, all of which are related. The experiments described include: quasistatic stress-strain tests (strains of 10[sup -4]--10[sup -1] at frequencies near dc-1Hz); torsional oscillator experiments (strains of 10[sup -4]--10[sup -7], frequencies between 0.1 and 100Hz); resonant bar experiments (strains of 10[sup -4]--10[sup -8], frequencies between 10[sup 3] and 10[sup 4] Hz); and dynamic, propagating wave experiments (strains of 10[sup -6]--10[sup -9], frequencies between 10[sup 3] and 10[sup 6] Hz). [Work supported by OBES/DOE through the University of California and the Institut Francais du Petrole.]