Abstract
Laboratory and numerical study tests were conducted to investigate the dynamic indentation characteristics for various spacings and indentation depths. First, laboratory tests indicate that the increase in the indentation depth first resulted in enlarged groove volumes, caused by fiercer rock breakages between indentations for a fixed spacing; then, the groove volume slightly increased for further increase in indentation depth, whereas the increase in spacing restrained rock breakages and resulted in shrunken grooves. In addition, the numerical study agreed well with laboratory tests that small chips formed at the shallow part of the rock specimen at the early indentation stage, and then, larger chips formed by the crack propagation at deeper parts of the rock specimens when the indentation depth increased. With further increase in indentation depth, crushed powders instead of chips formed. Moreover, the numerical analysis indicates that crack propagation usually leads to the decrease of the indentation force and the dissipation of the stress concentrations at crack tips, whereas the cessation of crack propagation frequently resulted in the increase of the indentation force and the stress concentrations at crack tip with the increase in indentation depth.
Highlights
Indentations by excavation tools have been widely used to simulate the rock breakage process that determines the indentation efficiency
Groove volumes, influenced by rock breakages, and indentation energy, determined by the indentation force, are two factors, determining the indentation efficiency. us, these two factors are mainly discussed
Numerical Tests e above laboratory tests indicate that rock breakages between indentations consisted of large chips, small chips at shallow parts, and crushed powders
Summary
Indentations by excavation tools have been widely used to simulate the rock breakage process that determines the indentation efficiency. Laboratory, and numerical studies indicated that cutting efficiency is affected by many factors, including geological and machinery factors. Gong et al indicated that joint spacing significantly affects the rock breakage mode and further influences the cutting efficiency [4]. Ma et al proposed in the numerical study that an optimal confinement appears in the indentation process for various confinements, based on various crack propagation degrees [7]. Besides the indenter shape and size, the indentation rate, and the loading sequence, the spacing and penetration (indentation depth) are the main machinery factors that may affect rock breakages and cutting efficiency [11,12,13,14,15]. The dynamic crack propagation that may determine the indentation force and the chip formation for various s/p ratios has hardly been investigated. With the laboratory results, the optimal s/p ratios were discussed
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