Abstract: As the cutting speed increases further, adiabatic shear localization fracture (ASLF) which is a fracture of adiabatic shear band (ASB) in serrated chip and makes segments separated completely inevitably. High speed machining experiment of hardened 45 steel (45 HRC) is carried out by using PCBN cutter with rake angle –10° at various speed up to 1 400 m/min and various feeds from 0.2 mm to 0.4 mm. The chip morphology, the cutting conditions and the corresponding changing regularity of energy in band are obtained. Combining gradient plasticity theory, the propagation model of thermo-plastic shear wave in serrated chip in high speed machining is established. Based on this theory, the expressions of adiabatic shear saturation limit (ASSL) and saturation degree (ASSD) are derived out, the fracture criterion of adiabatic shear localization is proposed and compare with the experimental results. The influences of shear band properties, material properties and loading conditions on ASLF are investigated. The shear band energy with cutting conditions can be described effectively by using ASSL derived from the propagation theory of thermo-plastic shear wave, which lays a theatrical and experimental foundation for the further study of predicting the occurrence of ASLF in serrated chip in the field of high speed machining.

Key words: Adiabatic shear localized fracture, Fracture criterion, High speed machining, Saturation limit, Thermo-plastic shear waves, Machining quality, Stack materials drilling, Titanium, Carbon fiber reinforced plastic