It was found that shearing forces on the shear plane were linear functions of the area on which they acted. This was observed for all materials investigated; for SAE 1112 steel, 2024-T4, and 6061-T6 aluminum alloys, and alpha-brass, and also is in agreement with data taken from the literature. Furthermore, all data examined showed that the straight line of shear force Fs versus area As intercepted the ordinate at a positive force value. This was interpreted to mean that the intercept part of the shearing force was used up in overcoming workpiece deformation or friction at the flank of the tool and was not available for chip deformation. Accepting this concept, it can then be shown that the average shearing stress on the shear plane for SAE 1112 is constant and is independent of normal stress, cutting speed, or strain rate, extent of deformation or finite strain, and extent of prior deformation. The shearing stresses for the other materials tested or examined were also constant for the limited range of variables available.
In contrast to the shearing stress, the normal stress on the shear plane was not constant and appears to be a yet unknown function of the mechanism of friction on the tool face.
The shearing stresses calculated from the metal-cutting data showed good correlation with flow stresses at the same finite strains which were obtained from static compression tests. The reason for the uniqueness of the finite strains at which correlation is achieved is not as yet clear.