Conclusions
The response of elastic/brittle targets to loading by conical-, wedge-and hemispherical-indenter shapes representing jackhammer bit tips was analyzed. Theoretical predictions of crack extent and direction are based on values of the maximum principal strains and the associated extension strain criterion in the target assuming a semi-infinite, homogeneous and isotropic solid.
Corresponding static experiments using an MTS machine and dynamic percussive tests involving an encased circular target disk of Sierra granite have been conducted. The damage pattern consisting of a crater, a crushed zone, a region of multiple minor cracks as well a some longer fissures has been delineated. Comparison with theoretical predictions indicate that cracks are produced by maximum tensile strain, with their directions predicted well by the present theory. The upper bound predictions of the crack extent are also in reasonable accord. Deviations are due to the presence of inhomogeneities and anisotropies in the tests specimens.
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Pang, S.S., Goldsmith, W. Investigation of crack formation during loading of brittle rock. Rock Mech Rock Engng 23, 53–63 (1990). https://doi.org/10.1007/BF01020422
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DOI: https://doi.org/10.1007/BF01020422