Characteristic Length of Quasi-Brittle Materials

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CMS-0070062"Characteristic Length of Quasi-Brittle Materials"PI: Joseph LabuzUniversity of Minnesota-Twin CitiesAbstract:Field and laboratory observations of rock failure indicate behavior quite different for structures of various size and shape. Due to the existence of a localized zone of microcracking, which seems to be a characteristic of the material, the nominal strength and the global response of a given geometry and load configuration of a rock structure are dependent on size. For many problems in geotechnical engineering (for instance, breakouts in tunneling, comminution and drilling, pullout of reinforcement), the characteristics of a localized zone are important in predicting failure. The objective of this research is to measure the characteristic length of various rocks. The localized zone of microcracking prior to failure will be mapped with locations of acoustic emission, and space-time clustering analyses will help to define the dimensions. As a complementary method, electronic speckle pattern interferometry will be used to measure surface deformation, providing a high resolution visual image of the displacement field. Numerical modeling with a distinct element code will provide a basis for the extension of the experimental results to other materials and conditions. By performing simulations designed to mimic the experimental measurements, the necessary constitutive behavior can be established, and the investigation of boundary value problems can be realized.