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.
Highlights
Forward rod extrusion is a well-established method for manufacturing metal components such as screws, bolts and axles in large series
To be able to more accurately model full-forward extrusion and arrive at improved prediction of forming induced residual stresses, a combined nonlinear isotropic/kinematic hardening model was calibrated for X6Cr17 (1.4016) steel, see Sect. 2.2
To study the effect of constitutive model on the predicted forming induced residual stresses on a workpiece made of X6Cr17 (1.4016) steel, a combined nonlinear isotropic/kinematic hardening model as well as the isotropic hardening part of the model were calibrated
Summary
Forward rod extrusion is a well-established method for manufacturing metal components such as screws, bolts and axles in large series. Process adopted mesh [15] and remeshing) and, ability of the employed constitutive model to accurately describe the Bauschinger as well as transient effects that are typically encountered in forming With regards to the latter, modeling of kinematic hardening at finite strains may have a significant effect on predicted residual stresses after forming, especially in cases of multistage forming [14]. Thereby, robust modeling of both the forming and the operation phases is a prerequisite for a correct numerical evaluation of the effect of different forming process parameters on fatigue life during operation In this regard, FE-modeling of a full-forward extrusion experiment with ejection of the workpiece is performed, adopting combined isotropic/kinematic as well as pure isotropic hardening models for the workpiece.
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