Seungjae Jung

Date of Graduation


Document Type



A fundamental study of impact indentation is presented for the dynamic penetration of a conical bit into coal block. Blocks of coal with approximate dimensions of 10 x 10 x 6 inches were laterally confined to predetermined equivalent in-situ stresses and then subjected to an impact indentation by dropping a coal cutting bit with a known weight from a known height. Tests were done with five bits of different geometry. The effect of material anisotropy on fracture formation was studied by testing coal specimens in face/butt cleat directions. General relationships between applied energy, bit geometry and damage zones on crater formation, fracture formation and fragment size distribution were studied. Bits with a narrow tip angle and a smooth body configuration exhibited better penetration at an optimum energy level. The dull and wider tip angled bits did not penetrate well into the specimen. Data collected from the experiments were used in building a statistical model to predict the relationship between input energy and damaged zone under a particular set of experimental conditions. The experimental results suggest that in coal cutting the trend should be toward using a sharper tip angled bit which consumes less energy for an optimum range of penetration depths, thus attaining maximum cutting efficiency and reducing fine fragments.