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Effects of Thermally Induced Microcracking on the Quasi Static and Dynamic Response of Salem Limestone

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Technical Report

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U.S. Army Engineer Research and Development Center, Geotechnical and Structures Laboratory Vicksburg United States

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The effects of microcracking on the mechanical properties of Salem limestone were investigated in three phases introduction of quantifiable levels of microcracks by thermal treating, mechanical testing of limestone samples with varying levels of microcracks, and modification of a numerical model to incorporate the measured effects. Computed tomography scanning, scanning electron microscopy, and optical microscopy OM were used to observe microstructural changes caused by the heat treatments. Mechanical testing was per-formed to characterize the mechanical response of the intact and damaged limestone. Quasi-static tests included uniaxial compression, triaxial compression, hydrostatic compression, and uniaxial strain constant volume tests. Microcracking did not affect the limestones strength at pressures greater than 10 MPa. Dynamic tests were performed using a modified split Hopkinson pressure bar. The results of the mechanical tests were used to modify the HJC model. Modifications were made to account for shear modulus degradation and failure surface changes. The original and modified HJC models were used in a numerical analysis of the mechanical tests performed in this work. The modified HJC provided better results for damaged material when compared with the quasi-static and dynamic experiments. This work demonstrated that this approach is useful for examination of the effects of microcracking on quasi-brittle materials and can be used to improve the predictive capabilities of material models.

Subject Categories:

  • Mechanics
  • Geology, Geochemistry and Mineralogy

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