A study of strain localization in the fine-blanking process using the large deformation finite element method

In this paper, an updated Lagrangian large deformation finite-element metho d was developed for solving metal forming problems with an incrementally ob jective mid-interval integration algorithm. In order to avoid oscillatory b ehaviour, the Green-Naghdi stress rate was adopted in the finite-element pr ogramme, this stress rate being determined implicitly by means of the rotat ion tensor. A consistent tangent operator and the Newton-Raphson iterative method were employed to solve the incremental equilibrium equations. The hy poelastic constitutive equations have been integrated numerically by the pr ojection algorithm. The target material is assumed to be a low-carbon steel having a stress-strain relationship which exhibits strain hardening and da mage softening. With this model, a numerical computation of strain localiza tion in the fine-blanking process was conducted. The computed deformed mesh agrees with experimental observation. The calculated equivalent plastic st rain was high at the clearance zone and the plastic flow was localized in t his area. Thus, the localization of plastic flow may cause the initiation o f shear bands. Under the high hydrostatic stress of the fine-blanking proce ss, further increase in the strains within the shear band will not contribu te significantly to the overall deformation of the material. Hence, shearin g fracture will occur at the cutting edges and a good cutting surface can b e achieved. (C) 1999 Elsevier Science S.A. All rights reserved.