A New Approach to Determine Cutting Forces in Brittle Rock Under Hyperbaric Conditions

Merchant (1944), (1945A) and (1945B) derived a model for determining the cutting forces when machining steel. The model was based on elastic-plastic deformation and a continuous chip formation (ductile cutting). The model included internal and external friction and shear strength, but no adhesion, gravity, inertia and pore pressures. Later Miedema (1987 September) extended this model with adhesion, gravity, inertial forces and pore water pressures. These models however only describe the so called Flow Type of cutting process, which is the ductile cutting process. The ductile cutting process requires a relatively large tensile strength (BTS) compared to the compressive strength (UCS) or shear strength. If the tensile strength is not large enough, brittle failure based on tensile failure may occur. This paper describes a new method of determining the cutting forces resulting from brittle failure, still based on the original ductile models, but with a correction for the stresses. This new model can be used for Deep Sea Mining Applications. It is assumed that materials which behave brittle under atmospheric conditions will behave ductile under hyperbaric conditions.