*3.1. R-Value Calculation*

The equation to calculate R-value is shown as Equation (8).

$$R = \frac{\varepsilon\_2}{\varepsilon\_3} \tag{8}$$

3 where *ε*2,*ε*<sup>3</sup> represent the true width strain and true thickness strain, respectively.

4

2 , <sup>3</sup> For sheet metals, the R-value is usually determined from three different directions of in-plane loading (0 ◦ , 45 ◦ , 90 ◦ in the rolling direction) and the normal R-value is calculated using the following equation:

$$R = \frac{1}{4}(R\_0 + 2R\_{45} + R\_{90})\tag{9}$$
