Revealing highly complex elastic nonlinear behavior of Earth materials applying dynamic acousto-elastic testing (DAET)
Résumé
A reliable physics-based theory that directly relates material elastic nonlinearity to damage and other features that may be responsible for the elastic nonlinear response (inter-grain soft bonds, dislocations) does not yet exist. Dynamic acousto-elasticity has significant implication to development of a physics based theory. The method provides the means to dynamically study the wavespeed -strain and attenuation-strain behaviors through the full wave cycle in contrast to most methods that measure average response. The method relies on exciting a sample with a low frequency vibration (several kHz) of strain amplitude ranging from 10-7 to 10-5 in order to cycle it through stress-strain multiple times. Simultaneously, a high frequency ultrasonic source (2 MHz) applies pulses with high repetition rate to read variations in elasticity and dissipation. By integrating the velocity-stress data, we extract the dynamic stress-strain behavior. Thus the low frequency amplitude-dependent anelastic energy dissipation can be assessed. We report preliminary results in 11 different room-dry rock samples, including a crystalline rock (granite), sandstones and limestones. The behaviors of the 6 investigated sandstones show a striking similarity, although they have different microstructures. We also show how acoustical conditioning can modify nonlinear elastodynamics, bringing temporarily the material in a metastable state.
Domaines
Acoustique [physics.class-ph]
Origine : Fichiers éditeurs autorisés sur une archive ouverte