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

A new method for evaluating the yield stress σ0.2 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 (4.9x10-2 mN) to 50 g (49 mN), and their results are compared with those of the Vickers hardness (Hv) at 200 g (1.96 N) and of tensile tests. The method is based on Cahoon et al.'s relation that σ0.2(MPa)=3.27 Hv(0.1)n and is composed on (i) the determination of the relationship between Hv and ultra-microhardness (Hum), (ii) the evaluation of n through analyzing the load dependence of Hum and (iii) the evaluation of σ0.2 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 σ0.2 evaluated from the present method, shows good coincidence with that obtained by tensile tests. (orig.)