Strain analysis in machining using metallographic methods

Strain patterns in 4340 steel chips created during turning at speeds between 36 and 440 m/min (119 and 1442 sfpm) are examined metallographically. A new method, based on the grain elongation orientation in the chip, is developed for quantification of local strains created during plane strain deformation in the primary and secondary deformation zones. This method is applied to both continuous and to sawtooth type chips. Strains determined by this method compare well with strains computed from chip thickness measurements, but there appear to be systematic differences. Strain localization is evident in chips formed at the higher cutting speeds. This strain localization does not appear to extend to the rake face side of the chip. The shear angle calculated from the strain in the strain-localized regions compares favorably with the orientation of these regions.