Modeling of Anisotropy Evolution in Pearlitic Steel
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2013
In a pearlitic structure, large deformations lead to a re-orientation and alignment of cementite lamellae on the microscopic level. These changes in the microstructure of pearlitic steel under large plastic deformations induce
substantial degrees of anisotropy in certain mechanical properties of the material like yield limit, fracture toughness and fatigue threshold values. The alteration and induced directional dependence in these specific properties is equivalent to changes in resistance against initiation and growth of fatigue cracks and as the result influences the fatigue life of the components. In the present work a material model formulated for large strains has been utilized to predict the evolution of anisotropy and to obtain the altered state of stress in the heavily deformed pearlitic steel components. In the developed material model, the macroscopic anisotropy evolution is motivated from homogenization of an ideal pearlitic microstructure. The evolution of anisotropy is modelled via an areal-affine re-orientation. On the microscopic level, material yielding is assumed to be mainly caused by shearing of the ferrite between the cementite lamellae. This assumption motivates a macroscopic yield criterion that is influenced by the re-orientation of the cementite lamellae. The evolution of anisotropy, thereby, leads to a distortional hardening of the yield surface. Both kinematic and isotropic hardening are included in the model. The material model has been calibrated against some experimental results from both cold drawing of pearlitic steel wires and high pressure torsion tests. Model predictions are later utilized to verify the hardness profiles measured in pearlitic steel railway components which are typically subjected to simultaneous large compressive and shear loads. It is believed that such a model can be further used as a reliable base to develop a crack initiation model for pearlitic steel.