Abstract: A theoretical model is proposed based on the Johnson-Cook law to predict the critical cutting speed for the onset of serrated chips in a high speed cutting process which takes into consideration the effect of the strain, strain rate and temperature on adiabatic shear. Critical cutting speeds are calculated for three workpiece materials of titanium alloy TC4, steel 45, and aluminum alloy 7050 with different space lattices. An analysis of the influence of material behavior parameters on the sensitivity of adiabatic shear is made by taking the critical cutting speed as the parameter and the sensitivity as the uniform criterion. Sensitivity of constitutive equation parameters is calculated and compared. Analytical results show that titanium alloy TC4 is the most sensitive of the three materials to adiabatic sheer. The hardening module and strain rate sensitivity coefficients have less effect on the adiabatic shear of steel 45 than on the other two materials. All J-C parameters have influence on adiabatic shear. Yield strength and hardening coefficient both play a significant part in the generation of serrated chips for all three materials studied in this paper. Except for TC4, the hardening module coefficient is the one factor which has less influence on the serrated chip, while the strain rate sensitivity and the thermal softening coefficients are located in a middle position.

Key words: adiabatic shear, cutting, strain rate, constitutive equation, sensitivity