The former is similar to bulge, but the deforming mode of the latter is rolling in which the stress is tensile in generatrix direction and the wall thickness are mainly reduced in this zone.
前者的受力情况类似于胀形，后者为母线方向拉应力作用下的辗压变形，该区起主要减薄壁厚的作用。
2
The expressions of elastic deforming volume and plastic deforming volume in the plastic zone were presented together with the average plastic volumetric strain.