Characterizing damage evolution and yield surfaces for Berea sandstone under triaxial loading as a function of effective pressure
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Copyright (2014) ARMA, American Rock Mechanics Association Granular porous material is idealized as an elastic-plastic material, where macroscopic failure occurs at a critical stress by localized dilatant shear at low effective pressure and compactional cataclastic flow at high effective pressure. Yielding and accumulation of microscopic damage at sub-critical stress levels are also important characteristics of the failure process. Here, load- reload triaxial compression tests are used to investigate damage development at low and high effective pressures, and test models of yield across the brittle-ductile transition. Water saturated cylinders of Berea sandstone were deformed at an axial strain rate of 10-5 s-1 and effective pressures of 20-240 MPa to investigate the dilational, transitional, and compactional regimes. Results illustrate that contours of equivalent damage for sub-critical stress states between yield and macroscopic failure are sub-parallel to the failure envelope except in the highest pressure regime. Damage induced at one effective pressure has a systematic, but variable effect on failure at other effective pressure conditions. The behavior across the transition from dilation to compaction is most consistent with a model based on two distinct yield envelopes, each associated with distinct damage mechanisms and a sharp transition between the low and high pressure regimes.