46th U.S. Rock Mechanics/Geomechanics Symposium,
2012. American Rock Mechanics Association
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The fracture process zone (FPZ), a zone of weakened material surrounding the tip of a propagating crack, is common to many brittle materials, and is likely related to brittle material damage mechanisms. This study follows recent investigations of Carrara Marble and asks whether microstructure size, such as the size of marble grains, leads to an different extent of damage for a brittle material. Existing work has used acoustic emissions or laser interferometry and optical microscopy to answer this question, and found a positive relationship between grain size and size of the FPZ. Our study uses nanoindentation to probe the nanomechanical properties of the FPZ for two marbles of varying grain size, and attempts to relate mechanical properties of the FPZ to grain size. The marbles are from Carrara, Italy (typical grain size 300 μm), and Danby, Vermont (typical grain size 520 μm). Grids of nanoindentations were placed within the FPZ regions of Danby and Carrara marble specimens. Both marbles exhibited lower nanomechanical properties near the crack tip and near the area of future wing-crack formation, i.e. the FPZ. However, the Danby (large microstructure) marble exhibited this trend over a larger distance, and thus provides nanomechanical support for the increase of the FPZ with grain size.
Fracture mechanisms at the micro- and nanoscales govern many important geomechanical processes, such as drilling in rock . An understanding of rock fracture at these small scales is thus critical to oil-, construction-, and other industries. The fracture process zone (FPZ) is a zone of damaged material surrounding the tip of a propagating crack [2,3]. This damage zone manifests itself in many brittle materials during fracture, and thus provides an opportunity to study fracture mechanisms. The FPZ of marble is the subject of this rock fracture study.
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