On theR-value measurements

Abstract

The plastic strain ratio,r, of a 1.2 mm (0.048 inch) thick AKDQ steel sheet has been determined by both the conventional indirect method and the direct method advanced in the present investigation. In the indirect method, the measured data were ε₁, and ε₂ and a linear relationship was observed between these two variables. By linear regression analysis of this relationship, the experimental scatter inr could thus be evaluated. In the direct method, the measured data were ε₂ and ε₃, the thickness strain, ε₃, being calculated from the measured weight difference of two identically prepared wafers “before” and after straining. It was also observed that ε₂ varied linearly with ε₃. To facilitate the experimental determination, a slightly tapered specimen capable of generating a set of experimental data was used in both methods. The experimental results showed that the strong dependence of r_m on ε₁ strain observed using the indirect method was greatly reduced or even eliminated within experimental scatter using the direct method. Experimental scatter inr could be reduced by a factor of 3 using the direct method in comparison with that using the indirect method. The determinedr-values are as follows: At ε₁ = 0.25 Direct Method Indirect Method 0 deg Orientation 1.76 ± 0.04 1.82 ± 0.12 45 deg Orientation 1.26 ± 0.02 1.24 ± 0.07 90 deg Orientation 2.17 ± 0.04 2.15 ± 0.19 •r_m 1.61 ± 0.03 1.61 ± 0.11