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Local Bifurcation and Instability Theory Applied to Formability Analysis
B.D. Buco,M.C. Oliveira,J.L. Alves,L.F. Menezes,K. Ito,N. Mori 한국소성가공학회 2010 기타자료 Vol.2010 No.6
Sheet metal forming components are typically studied with the aid of finite element method based virtual tryout tools, since they allow to save money, time and effort in the design, production and process set-up of deep drawn parts. In all these development phases the analysis of defects is performed with the aid of the material forming limit diagram (FLD), since it allows defining a safe region that reduces: (i) necking; (ii) wrinkling and (iii) large deformation occurrence. It is known that the FLD represented in the strain space presents some disadvantages. The local bifurcation criterion proposed by Ito and Goya defines the critical state for a local bifurcation to set in, as a function of the stress level to work-hardening rate ratio. Thus, the main advantage is that the FLD represented in the stress plane is completely objective [1]. In this work the Ito and Goya model is used to evaluate formability, as well fracture mode and direction along different strain paths: (i) uniaxial tension; (ii) equibiaxial stretch; and (iii) plane-strain. All numerical simulations are performed with the in-house code DD3IMP [2, 3] and NXT [4] in which the Ito and Goya model is implemented, is applied to analyze the results.