Towards an holistic account on residual stresses in full-forward extruded rods

Abstract

An holistic view is attempted towards prediction of the effect of residual stresses induced by full-forward extrusion on fatigue life of workpieces during operation. To study the effect of constitutive model on the accuracy of forming simulations, a combined nonlinear isotropic/kinematic hardening model as well as the isotropic hardening part of the same model are calibrated based on five compression-tension-compression uniaxial stress experiments. A full-forward extrusion finite element model is developed adapting both the aforementioned hardening plasticity models and the predicted residual stress states at the surface of the workpiece are compared against that of a corresponding forming experiment. Results show residual stress predictions of remarkable accuracy by the FE-models with the isotropic hardening model. The effect of residual stresses on fatigue life of the workpiece is qualitatively studied by uncoupled multiscale simulations featuring gradient crystal plasticity at the microscale. While the effective (homogenized) macroscale response indicates elastic response during a macroscopically cyclic loading, plasticity accompanying reduction of residual stresses is still present at the microscale within, e.g. grain boundaries.

Component residual stress control in forward rod extrusion by material flow and tribology—experiments and modeling

“…A 2D large strain axisymmetric FE-model for full forward extrusion in the commercial FE-analysis software MSC Marc [25] is further elaborated here using the model developed by the authors in [22] and optimized in [8] as a point of departure. The model is comprised of the continuum parts, shrink ring, die and workpiece, as well as the rigid parts, bottom plate, top plate, punch and ejector, see Fig.…”

“…More specifically, three FE-meshes are considered for the workpiece featuring 25,248 (coarse), 42,912 (fine) and 67,450 (finest) degrees-of-freedom. In contrast to [22] and [8], where a process-adapted mesh was used, a regular FE-mesh for the workpiece comprised mostly of rectangular elements is used here to resolve the full forward extrusion problem. Fixed and relatively coarse discretizations are considered for the shrink ring and the die with a finer mesh for the latter in the shoulder region.…”

“…Fixed and relatively coarse discretizations are considered for the shrink ring and the die with a finer mesh for the latter in the shoulder region. The built-in Marc Chaboche [5] combined nonlinear isotropic/kinematic hardening model is used as a constitutive model for the workpiece with the model parameters identified in [8] based on compression-tension-compression uniaxial stress experiments, see Table 1. This is an improved constitutive modeling approach compared to the pure isotropic hardening model used in [22].…”