HR: 0800h
AN: T41B-0583    [Abstracts]
TI: Strain Localization due to Structural Softening During Pressure Sensitive Yielding
AU: * Le Pourhiet, L
EM: pourhiet@ccr.jussieu.fr
AF: Laboratoire de tectonique, UPMC Paris 6, 4 place Jussieu, Paris, 75005, France
AU: Podladchikov, Y Y
EM: yuripo@fys.uio.no
AF: PGP,University of Oslo, PO Box 1048 Blindern, OSLO, 0316, Norway
AB: Mohr coulomb non associated flow rule l is able to catch the main characteristic of brittle behavior i.e. pressure sensitivity and relatively small volumetric strain versus shear strain observed in shear bands with only two plastic parameters (φ and ψ). Without any further increase of complexity of rheological model, it is sufficient to explain strain self-localization in granular material with predictions that are compatible with major observations such as the occurrence of localization within hardening regime, orientation of the localized zones and their diversity.
For non rate dependant material, the problem is found to be solvable analytically as a system of linear equation for which we derived analytical expression for the maximum stress drop a shear band may produce, for the equivalent tangent modulus and rate of rotation of the stress within the band as a function of shear band orientation.
Performing a parametric study, we found a good approximation for the characteristic strain necessary for a shear band to achieve its maximum stress drop. This reveals that pressure sensitivity is not only related to friction but that elasticity also affects the scale of the displacement needed to achieve stress drop. This effect, often neglected when scaling experiments to nature, may lead to effective brittle plastic in the laboratory which does not have to exist in nature (or the opposite with sand box type analogue experiments in the field of tectonics).
Within this model, the most favorable orientation for shear band evolves with strain so that, in a system which is not kinematically locked, the MC model predicts changes in the orientation of the strands with strain and part of the complexity of natural shear bands.
For rate dependant material, numerical experiments were used to quantify the strain rates at which brittle ductile transition occurs. We show that in that case, the brittle plastic transition occurs as a function of confining pressure and strain rate and that at that level, a small domain exists where the shear zones harden with decreasing the viscosity.
DE: 4475 Scaling: spatial and temporal (1872, 3270, 4277)
DE: 5120 Plasticity, diffusion, and creep
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8163 Rheology and friction of fault zones (8034)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting