Shear-Strain Rate in Metal Cutting and Its Effects on Shear-Flow Stress

Abstract

A relationship is derived from which the average shear-strain rate in the shear zone, during orthogonal as well as oblique cutting, may be calculated if the average shear-zone thickness is known. A method of determining the average shear-zone thickness is described, which involves the use of a mechanism that stops the cutting process practically instantaneously and thus “freezes” the process of chip formation. The variation of the shear-zone thickness and of the shear-strain rate with the normal rake angle, the inclination angle, the feed, and the cutting speed when dry-machining SAE 1015, 118 Bhn seamless-steel tubing is determined. The average shear-zone thickness is found to vary from 0.0007 to 0.007 in. and the average shear-strain rate from 2500 to 212,000 per sec. The shear-flow stress in the shear zone is calculated and found to be 2⅓ to 3¼ times the static shear-flow stress of approximately 26,000 psi. The effect of the shear-strain rate on the shear-flow stress in the shear zone is analyzed and it is found that an increase in the shear-strain rate is accompanied by a significant increase in the shear-flow stress.