Forming Limits for Anisotropic Sheet Metals

Most failures of ductile materials in metal forming processes occurred due to material damage evolution-void nucleation, growth and coalescence. In this paper, modified version of Gurson-Tvergaard's yield function in conjunction with the Hosford's non-quadratic anisotropic yield criterion is studied to clarify the plastic deformation characteristic of voided anisotropic sheet metals. The void growth of an anisotropic sheet under biaxial tensile loading and damage effect of void growth on forming limits of sheet metals are investigated. Also the characteristic length defining the neck geometry is introduced in M-K model to incorporate the effect of triaxial stress in necked region on forming limits. The forming limits theoretically predicted are compared with some experimental data. Satisfactory agreement was obtained between the predictions and experimental data.