Rock cuttability assessment using the concept of hybrid dynamic hardness (HDH)

Hybrid dynamic hardness (HDH) is an indentation-based rock hardness concept which is a formulated combination of the surface rebound hardness and the deformation ratio of a given rock material. This new concept was recently put forward by one of the present authors and was successfully applied to estimate the uniaxial compressive strength of carbonate rocks. So far, there has been no application of this hardness concept to rock cuttability assessment. Considering this fact, the present work was performed to examine the tenability of the HDH concept in rock cuttability assessment, in relation to the prediction of rock cutting specific energy, cutting forces, and the field cutting performances of some mechanical excavators. To achieve these goals, the authors have statistically evaluated a wide variety of laboratory and field data previously reported in the literature. Results of the statistical analyses indicate that the HDH testing procedure employed in the present work has the potential to be used as an index rock material property that can be employed in preliminary estimations of specific energy, cutting force, and normal force for a wide range of rocks under different operational conditions involving conical cutters (tip angle 80°, attack angle 55°, relieved cutting mode at optimum spacing to depth of cut ratio) and chisel cutters (rake angle −5°, clearance angle 5°, tip width 12.7 mm, cutting depths 1, 2, and 3 mm, unrelieved cutting mode). The close correspondence also observed between the calculated HDH values and the field-measured net cutting performance values of a roadheader and some chainsaw machines provide further evidence of the usability of this concept for rock cuttability assessment purposes.