Material behaviour in deformation zones of machining operation

Abstract

A re-evaluation of the factors affecting the flow strength of materials in the metal-cutting operation has been made by comparing experimental machining data with results from the dynamic shear testing and punching of metals. An analysis of the primary shear zone, made on the assumption that all the plastic work is done in a discrete, parallel-sided region, has been used to calculate the values of n and σ_l in the schematic stress-strain relationship σ=σ_l(ε)ⁿ. Results are presented for commercially pure copper in the shear strain rate range 0·1–7 × 10⁴S⁻¹ and for low-carbon steel in the range 0·1–20 − 10⁴S⁻¹. It is also demonstrated that the flow strength of these materials in the secondary shear zone is considerably lower than the strength in primary shear and is comparable with the yield stress values. The physical significance of these results is qualitatively discussed in terms of the equivalent stress-strain relationships under warm-working conditions.