| Flatness defects in thin strip cold rolling are a consequence of roll thermo-elastic deformation and the resulting heterogeneous strip plastic deformation. But in the case of on-line, manifested flatness defects, buckling reorganizes the stress field in the pre- and post-bite areas, which might impact strain and stress fields in the bite or at its ends. Such effects have always been neglected in the past. The purpose of the present paper is to present two coupled approaches to examine to what extent such potential in-bite / out-of-bite feedback determines the in-bite fields and the flatness of the strip. Using both methods and comparing with the standard case where buckling is not accounted for, it has been shown that (i) taking buckling into account results in completely different stress fields and fits correctly the measured on-line residual stresses under tension ("stress-meter rolls"); (ii) coupling buckling in the post-bite area and the rolling model, whatever the technique, changes little the in-bite fields; differences, if any, concentrate in the immediate vicinity of the bite exit; (iii) but in the case where manifested flatness defects occur, these tiny interactions (namely, through the exit velocity transverse profile) are essential for the precise description of the residual stresses and for accurate flatness prediction. |
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