Chip formation, acoustic emission and surface white layers in hard machining

In hard machining, sawtooth chip formation is due to initiation of adiabatic shear within the lower region of the primary shear zone. Catastrophic failure within the upper region of the shear zone occurs through either of two different mechanisms and results in the rapid release of elastic strain energy. This periodic release of strain energy is the dominant source of acoustic emission during sawtooth chip formation. In addition to adiabatic shearing in the primary and secondary shear zones, there is evidence to suggest that it occurs in the tertiary shear zone also; namely the surface white layer.