Effect of Microstructural and Morphological Parameters on the Formability of BCC Metal Sheets

Abstract

The determination of forming limit strains in sheet metal forming industry is a useful way for quantifying metals in terms of formability. However, such forming limit diagrams (FLDs) remain very difficult to obtain experimentally. Therefore, the numerical prediction of forming limit strains represents a convenient alternative to replace this time consuming and expensive experimental process. Moreover, a combined theoretical‐numerical model allows investigating the impact of essential microstructural aspects (e.g., initial and induced textures, dislocation density evolution, softening mechanisms, …) and deformation mechanisms on the ductility of polycrystalline aggregates. In this paper, the impact of microstructural and morphological parameters, particularly the mean grain size, on the formability limit of BCC materials is investigated. To this end, an elastic–plastic self‐consistent (EPSC) polycrystalline model, coupled with a bifurcation‐based localization criterion, is adopted to numerically simulate FLDs. The FLDs thus determined using the Bifurcation–EPSC model for an IF–Ti single‐phase steel are compared to the FLDs given by ArcelorMittal, demonstrating the predictive capability of the proposed approach in investigations of sheet metal formability. The role of the averaging scheme is also shown to be significant by comparing the critical limit strains predicted with the self‐consistent scale‐transition scheme to those obtained with the more classical full‐constraint Taylor model. Finally, numerical simulations for different values of mean grain size are provided in order to analyze the impact of mean grain size on the formability of BCC metal sheets.

Elastoplastic deformation and damage process in duplex stainless steels studied using synchrotron and neutron diffractions in comparison with a self-consistent model

“…More recently, this scale transition model was applied to study the influence of intragranular microstructure on ductility and forming limits in multiphase steels or single phase b.c.c. steel (Franz et al, 2014), and analysis of stress localization for polycrystalline material (Franz et al, 2013). The same model was also used for the interpretation of diffraction measurements performed for two-phase duplex steels (Baczma nski and Braham, 2004;Baczma nski et al, 2011;Wro nski et al, 2007).…”

Diffraction Methods and Scale Transition Model used to study Evolution of Intergranular Stress and Micro-Damage Phenomenon during Elasto-Plastic Deformation

“…The model developed by Berveiller and Lipinski describes the behaviour of a polycrystalline material for large strains, taking the rotation of the crystal lattice into account. The latter method was used by many authors to predict elastoplastic deformation and texture evolution in polycrystalline materials [8][9][10][11].…”

Stress distribution correlated with damage in duplex stainless steel studied by synchrotron diffraction during plastic necking

“…The self-consistent model of elastoplastic deformation elaborated by Lipinski and Berveiller [40,41,43,44] was used to interpret the experimental results as well as to determine the parameters of Voce law [29,42] in each phase of the studied duplex steel. In these calculations the initial orientations of crystallites, corresponding to the experimental textures [29], single crystal elastic constants given in Section 3.2 (the same as for the XEC calculation) and the initial stresses (listed in Table 2) were used as the input data for each phase.…”

“…C 11 [GPa] C 22 [GPa] C 33 [GPa] C 12 [GPa] C 13 [GPa] C 23 [GPa] C 44 [GPa] On the out-necking area, the mesh with free structured tetrahedral element was used and the element seeds were assigned every 0.5 mm along the edge of the model. The same type of element was applied for the mesh of the in-necking area, but the distance between the element nodes was reduced to 0.05 mm in order to acquire a more accurate result along the necking zone.…”