A new method for evaluating stress-strain properties of metals using ultra-microhardness technique

A new method for evaluating the yield stress σ_0.2 and the strain-hardening exponent n of metals is proposed through ultra-microhardness (UMH) technique with an application to fcc metals. UMH measurements with a triangular-base pyramidal indenter have been conducted on copper and copper-aluminum alloys under cold-rolled and annealed conditions at loads ranging from 0.05 g (4.9 × 10^-2 mN) to 50 g (49 mN), and their results are compared with those of the Vickers hardness (H_v) at 200 g (1.96 N) and of tensile tests. The method is based on Cahoon et al.'s relation that σ_0.2(MPa) = 3.27H_v (0.1)ⁿ and is composed of (i) the determination of the relationship between H_v and ultra-microhardness (H_um), (ii) the evaluation of n through analyzing the load dependence of H_um and (iii) the evaluation of σ_0.2 from Cahoon et al.'s relation together with the results on (i) and (ii). The value of n can be extracted through the UMH test, and the value of σ_0.2 evaluated from the present method, shows good coincidence with that obtained by tensile tests.