ANALYSIS OF THE UNIQUE MECHANICS OF SHEAR LOCALIZATION IN METAL CUTTING PROCESSES

Recent experimental observations show that the frequency of stress and temperature fluctuations on the cutting tool's rake face and the frequency of residual stress fluctuation at the finished surface of the workpiece are equal to the shear band formation's frequency. In this article, new experimental observations of the shear band formation in cutting processes are presented. Then, the spacing between neighboring shear bands (which determines the shear band formation's frequency) is obtained from different theoretical methods and compared with the experimental results. It is shown that the shear band spacing in cutting processes cannot be obtained from the theories developed in other dynamic deformation applications, including dynamic compression and torsion tests and ballistic impacts, due to the unique mechanics of cutting. In addition, we show that due to the intense plastic deformation in the primary deformation zone, the cooling rate of the shear band formed during cutting processes is considerably higher than the workshop cooling rates (6.85x10(8) K center dot s(-1) for the cutting speed of 60 m center dot min(-1) compared to 50 K center dot s(-1)- 2x10(4) K center dot s(-1) for workshop cooling rate of Ti-6Al-4V). The rapid cooling rate indicates the considerable amount of heat transferred into the cutting tool and explains the ductile to brittle transition in the fracture mechanism of shear band formation in cutting processes.