Coupled and uncoupled approaches for thin cold rolled strip buckling prediction

Severe thin strip cold rolling conditions usually induce heterogeneity of in-bite plastic deformation always translated to irregular stress field. This stress field may dwell sufficiently compressive in several out-of-bite areas to cause buckling (flatness defects) which generates stress reorganisation in rolled strip and probably affects the bite zone. Hence, out-of-bite buckling, in-bite elastic-(visco)plastic deformation and thermo-mechanical roll-stack/strip interaction may be strongly coupled. However, a completely coupled model providing realistic rolled strip shape specially when flatness defects occur is not easy to establish. This call for two ways of flatness defect modelling in thin strip rolling: with a completely coupled approach but using a simple buckling criterion, or using an uncoupled approach by chaining strip rolling model calculation with shell element models presenting good buckling computing capabilities. Our objective is the improvement of the flat product rolling - specialized FEM software Lam3/Tec3 [1] using Counhaye simple buckling criterion [3] and Asymptotic Numerical Method (ANM) for shell element model [9, 10] respectively with coupled and uncouple approaches detailed in the present paper. These two approaches bring computed stress profiles to very good agreement with experiments and the most important result at this stage is the weak influence of buckling on in-bite stress and strain fields providing a more rigorous justification of the traditional decoupled methods [2,5-8].