Improved fracture criterion to chain forming stage and in use mechanical strength computations of metallic parts – Application to half-blanked components

Abstract : Forming processes stages usually affect final components mechanical properties. Accounting for material processing effect is required to analyze final component's mechanical strength and optimize products design. Accounting for both the forming stage and the structural analysis of the final product requires dealing with complex multi-stages and non-proportional loading configurations. The development of improved material models and numerical methods is needed. In the present paper, in-use mechanical behavior of half-blanked components is modeled by means of the finite element method. The complete methodology to chain metal forming computations (Forge® software) and in-use parts mechanical loading computations (LS-Dyna® software) is described. An improved fracture criterion, suited for the non-proportional loading observed during products lifecycle, was developed and used to model fracture of high-strength low-alloy steel S420MC. Ductility is modeled by a damage variable which can grow during the forming stage allowing the modeling of the relative loss of ductility induced by this step. The proposed fracture criterion is based on the definition of stress state functions, by parts in the stress states space, which allows modeling fracture under a wide range of loading conditions. Laboratory tests and industrial case computations results are assessed by comparison with experiment. Influence of forming stage and ductile fracture is analyzed. It is shown that accounting for the manufacturing process and modeling fracture are mandatory if one wants to predict accurately the observed failure modes as well as the load-carrying capacity of half-blanked components.