Fracture toughness, chip types and the mechanics of cutting wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Historical studies for predicting cutting forces in wood processing are based on the Piispanen/Ernst-Merchant theory employed in metal cutting where the offcut/chip is formed in shear. This analysis has been recently improved to include significant work of surface separation and formation (i.e., the fracture toughness of the workpiece, as well as the shear yield stress and friction). The new theory is applied here to wood cutting experiments. It is well known that chip formation and surface damage depend on grain orientation and chip thickness, but experiments reveal that chip formation alters with cutting speed as well. During the COST E35 action a series of experiments and special devices to orthogonally cut wood at high and low speed have been developed. In this paper, an overview of the cutting devices and the main results are given.