Analysis of Stretch-Forming Double-Curved Sheet-Metal Parts

Double-curved surfaces, typical in airplane design, are classified according to direction of curvature. A qualitative stress analysis is made of stretch-forming (process of clamping metal sheet at two opposite edges and forcing a punch into the taut sheet) each class of surface, with special reference to the stress transverse to the direction of restraint. It is shown that there are two distinctly different sources of transverse stress during stretching. The resultant stress may be tension or compression, depending upon the direction and amount of curvature. When the resultant transverse stress is compression, undesirable wrinkling of the sheet may occur.