*3.2. Lankford Value of Starting Materials*

*ε* Figures 5 and 6 show the stress-strain curves and Lankford values *r* of each starting material, respectively. The true strain εtrue in Figure 6 corresponds to that in Figure 5b. A drop in stress due to necking was not observed for all materials, as shown in Figure 5a. Necking was observed only on the fractured surface of the copper tube. It is considered that necking occurred immediately before the fracture. Therefore, the strain from necking to fracture was negligible. The measured fracture strain of the aluminum alloy tube was 0.31. Therefore, the Lankford values *r* of the aluminum alloy tube at the true strain of 0.34 and 0.41 could not be measured. The Lankford value decreased as the true strain increased for each material. The Lankford values decreased in the order of the aluminum alloy, the copper, and the stainless-steel tube at each true strain. *ε*

**Figure 5.** Results of the tensile test. (**a**) Nominal stress—nominal strain curves and (**b**) true stress—true strain curves. The symbol × indicates the fracture point.

**Figure 6.** Lankford value against true strain obtained by the tensile test of each material. The dotted lines indicate the eye guide.
