In this paper the applicability of J2 deformation theory to the stamping of circular sheets is discussed through the comparison of various cases whose loading paths deviate from proportional loading paths to varying degrees. It is seen that the potential of deformation theory is not as great as has previously been supposed.
Zhang, L. C., Yu, T. X., & Wang, R. (1989). Investigation of sheet metal forming by bending--Part III: Applicability of deformation theory to stamping of circular sheets. International Journal of Mechanical Sciences, 31(5), 327–333. https://doi.org/http://dx.doi.org/10.1016/0020-7403(89)90057-X