Intrinsic Nonlinearity in Geomaterials: Elastic Properties of Rocks at Low Strain

The elastic properties of geomaterials are anomalous. Hysteresis with end point memory, slow dynamics, and linear variation of the resonance frequency with the strain are only some of these uncommon features. All these characteristics have been related to a nonclassical nonlinear elasticity. Chapter 1 introduces two strain regions where the experiments show different elastic behaviors. At low strain, rocks show their intrinsic nonlinearity until a strain material-dependent threshold, th . A transition from linear to classical nonlinear behavior appears in this first region. For strains beyond th the experimental data are contaminated by a complex nonequilibrium dynamics. Memory effects and conditioning complicate the characterization of the intrinsic nonlinearity of the sample and they do not allow a simple interpretation of the experimental data to prove the existence of anomalous nonclassical nonlinearity.