When a sheet is bent and removed from the die, its bend angle partly recovers by elastic recovery (springback). Which is likely to show larger springback? Assume the same sheet thickness and bend radius.

Answer: C. A material with a high yield stress and a low Young's modulus

Even after plastic deformation, stresses of about the yield stress remain across the section of a bent sheet, and when the load is removed it springs back by the corresponding elastic strain (roughly σ/E). Springback is therefore larger the higher the yield stress and the lower the Young's modulus. High-strength steel sheet, with the same Young's modulus but higher strength, and aluminum alloy sheet, with a Young's modulus about one-third that of steel, show large springback and are harder to bring to shape. The option of a soft and stiff material is the reverse, and the option saying it is set only by the working speed is also wrong. Countermeasures include overbending by the amount of recovery and pressing the bend firmly in the die so that the bend region deforms plastically.