The Effect of Normal Pressure on Yielding During Sheet Forming

In most forming analyses, the stresses normal to the sheet surface are usually neglected, and the “plane stress problem” is the one being solved. Most FEA codes use shell elements in which the “third” stress component is not considered, or more properly, iterated until it goes to zero. This simplification yields accurate results for most cases. However, when high curvature bending under tension is present, the effect of the normal pressure on yielding is significant, and should be considered for more accurate results. This paper presents various analytical and numerical solutions that highlight and quantify such an effect.