| Summary: | 博士 === 國立臺灣科技大學 === 營建工程系 === 97 === When quasi-brittle rocks are loaded under different stress paths, fracture development led by the internal microcracks and localization may exist although the loading level has not reached the peak point. Therefore, studies on the correlations between microcrack development and the safety of macro-scale structure become rather important. Both the approaches of experimental and numerical analysis are adopted in this paper to investigate the fracture mechanism for quasi-brittle rocks under different stress paths.
In the experiments, ordinary Portland cement (OPC) paste, C190 cement paste, marble and serpentinite specimens are selected for uniaxial compression and Brazilian tests. As for the indentation test, C190 cement paste and marble specimens are used. Non-destructive acoustic emission (AE) technique is applied in the loading process for specimens (time characteristics) to measure the localization and distribution of microcracks and further on to compare the initial crack and propagation of macrocracks (space characteristics). Experimental outcomes show the trends of micro and macro scales are consistent. Meanwhile, theoretical solutions are proven matching very well with the experimental results.
For the numerical analysis, a discrete element code, PFC3D is used to simulate the testing processes of different stress paths (uniaxial compression and Brazilian tests) for marble specimen by the model fitting which satisfies physics meanings. Microfractures between particle contacts from numerical analyses are compared with AE microcracks in the experiments to verify the suitability of numerical analysis. Numerical analysis can assist more detailed studies of localization timings, normalized shear/tensile microcracks increment ratio (△S/△T) and failure mode.
Based upon the analysis, comparision and verification of fracture mechanism for experiments and numerical analyses and further to ensure the evolutions of the whole elastic, plastic and fracture processes, relevant guidelines regarding to non-destructive AE technique can be established. Moreover, input parameters verified reasonable in the numerical analysis can be provided for the application in the rock engineering practice as well.
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