Careful finite element simulations of cold rolling with accurate through-thickness resolution and prediction of residual stress

In this paper, we carefully develop a finite element (FE) model that gives accurate through-thickness predictions of stress and strain distributions during the steady-state cold rolling process. These through-thickness predictions unveil an oscillatory pattern that is shown to have important consequences for residual stress in the rolled sheet. We believe this is the first time that through-thickness FE results have been accurately validated by comparison to non-FE results, in this case by comparison to a recent analytical model of through-thickness variation in cold rolling. While we use here the ABAQUS commercially available FE software, our observations are relevant to all FE simulations of cold rolling. Care is taken by considering both convergence in number of elements through thickness, convergence to a steady state, and the avoidance of other numerical artefacts such as shear locking and hourglassing. We find that previous FE models of cold rolling are usually woefully under-resolved through-thickness; e.g. using 10 elements through-thickness, while we require 60 here for convergence. Convergence of roll force and roll torque, used in previous studies to validate models, are shown to be poor indicators of through-thickness convergence. We also show that the through-thickness oscillatory pattern may have important consequences for predicting curvature during asymmetric rolling.