科研之友
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摘要
This paper presents a two-surface elastoplastic model for brittle-ductile transition behaviors of porous rocks subjected to compressive stresses. Two plastic deformation mechanisms are taken into consideration: plastic shearing at low confining pressure and plastic pore collapse at high confining pressure. For loading in the brittle regime, a unified hardening/softening law is introduced into the Drucker-Prager-type yield criterion to describe the pre-peak hardening and post-peak softening behaviors. A non-associated flow rule is adopted to capture the volumetric compressibility-dilatancy phenomenon. For loading in the ductile regime, a monotonic strain hardening law as a function of hydrostatic stress is proposed and incorporated into the DiMaggio-Sandler-type yield criterion. A non-associated flow rule is used to realistically describe the plastic compaction response caused by non-hydrostatic stress. An analytical solution of stress-strain relations for shear surface is developed in the case of conventional triaxial compression. Based on the bifurcation analysis, the onset of strain localization along cap surface is predicted. Comparisons between numerical simulations and experimental data show that the proposed model is able to capture the main mechanical behaviors of the investigated porous rocks, Adamswiller sandstone and Bentheim sandstone, including strength nonlinearity, strong pressure sensitivity, strain hardening/softening, volumetric compaction/dilation, and brittle-ductile transition.
