Finite element simulations on void closure behaviour inside the sheet during sheet rolling processes

The purpose of this paper is to explore the deformation mechanism of voids and stress-strain distributions around internal voids inside the sheet during sheet rolling processes. The plastic deformation and flow pattern of sheets during sheet rolling were simulated by the finite element method. The influences of various rolling conditions, such as the thickness reduction, the dimension of the internal void, friction factor, cross-sectional area of the void, etc., on the dimension of the void at the exit are discussed. The critical thickness reductions, over which the void would close completely, were also investigated. Furthermore, experiments on sheet rolling with an internal void inside the sheet were conducted. Theoretical predictions of the dimension of voids after rolling were compared with experimental results and relatively good agreement between them was found. Clearly, these analytical results can provide useful knowledge for designing the pass-schedule of sheet rolling processes for eliminating internal voids.