There's no requirement that the blank for a part be square.
The ratio of blank edge lengths is irrelevant.
In bending, whether by hand or by power brake, the material is caused to yield, typically to a small but finite radius. That's an intentional change of shape. The only distortion, meaning here unintended change of shape, is that the material swells a little at the inner radius where it contacts the punch, and also the width shrinks a little in the same area. Within the width of the material, a compressive stress is induced at the inner radius, and a tensile stress is induced at the outer radius. At the edges, there's no material to resist that stress, so it manages to produce a strain. That's a little simplified, but I think it answers your question as I understood it.
Mike Halloran
Pembroke Pines, FL, USA
