The fracture mechanics of surface layer removal

A general solution is given for the removal of a surface layer either by a sharp tool or by a peeling force. The creation of the separated layer is treated as a fracture process and analysed using an energy approach. For the cutting case frictional work at the tool-layer interface is included. Elastic cutting is first analysed and then that involving plastic bending which results in the layer curling. The transition from elastic to elastic-plastic bending occurs when ({frac{sigma_y²h}{2EG_c}}) . For small values of this parameter and high cutting angles there is a further transition to plastic shearing in the layer which leads to lower cutting forces. It is shown that both in this, and in some bending cases, there can be touching of the tool at the fracture which changes the nature of the process. The peeling case is shown to be a special, zero friction, version of cutting in which both elastic and elastic-plastic bending can occur. However plastic shearing is shown not to occur as it is energetically less favourable. Some comments on crack veering in high thickness cuts from mode II effects are made. Such deviations in direction can lead to none steady propagation.