As noted in Fig. 7.16, the state of stress shifts from plane stress to plane strain as the ratio

of length-of-bend to sheet thickness increases.

Explain why. This situation is somewhat similar to rolling

of sheet metal where the wider the sheet, the

closer it becomes to the plane-strain condition.

In bending, a short length in the bend area

has very little constraint from the unbent regions,

hence the situation is one of basically

plane stress. On the other hand, the greater

the length, the more the constraint, thus event