Quantitative Observation of the Micromechanics of the Brittle-Ductile Transition in Rocks

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The transition in failure mechanism from brittle fracture to plastic flow is important in understanding tectonophysics, the strength of the crust, and the style of deformation at the field scale. Recent studies in three areas have yielded new insight into the physics and mechanics of the brittle-plastic transition: acquisition of high quality mechanical data, systematic observations of deformation microstructures, and advances in the theoretical modeling of the failure of rocks in compression. Qualitative microstructural observations have provided information on the conditions under which various deformation mechanism operate, estimates of strain partitioning, and identification of crack nucleation mechanism. The PI will continue work on the brittle-ductile transition by performing triaxial mechanical tests on natural and synthetic rocks of calcite, anorthite, peridotite, and diabase. Quantitative microstructural analyses to understand the micromechanics of deformation are an important part of this study. Acoustic emission measurements will also be performed on a selected number of experiments, and axial and volumetric strain measurements will be made during the tests.