In extrusion of metals, which of the following statement(s) is/are true?

In a tensile test of ductile material, necking starts at

A. lower yield stress

B. upper yield stress

C. ultimate tensile strength

D. just before fracture

A metallic sheet 1 m wide and 10 mm thick is to be rolled under a front tension force of 100 KN. A specimen from the sheet, tested under tension, shows a yield stress of 100 MPa. Assume plain strain condition during rolling and ignore the friction. If yielding is assumed to start at a roll pressure of σ3 MPa, then the stress in the width direction (where strain is zero) is

A. $$2 + \frac{{\sigma 3}}{2}$$

B. $$4 + \frac{{\sigma 3}}{5}$$

C. $$5 + \frac{{\sigma 3}}{2}$$

D. $$5 + \frac{{\sigma 3}}{3}$$

Match the forming methods in Group 1 with the defects in Group 2.

A. P-1, Q-2, R-3

B. P-4, Q-3, R-1

C. P-3, Q-1, R-4

D. P-2, Q-1, R-3

The maximum axial compression stress during cold upsetting of a cylindrical rod of radius, 'r', occurs at

A. the outer edges of the rod

B. $$\frac{r}{3}$$ from the centre

C. $$\frac{r}{2}$$ from the centre

D. the centre