Experimental Investigation and Modeling of Dynamic Recrystallization
Zusammenfassung der Projektergebnisse
In the past, several attempts were made to find a correct physical model for DRX. In the present research program, a variational model for DRX was developed which takes all the different facets of dynamic recrystallization into account. The mechanical aspects are formulated within the framework of rate-independent large-strain Cosserat plasticity. The model accounts for immobilized dislocations and incorporates partitioning into subgrains, grain movement and grain growth within the polycrystal as well as recovery. Softening is included by a stochastic rate equation. Dynamic recrystallization takes place during the plastic deformation. After severe difficulties, finally a L-BFGS quasi-Newton method based on finite differences could be implemented in 3D to solve the finite-strain Cosserat model. In the experimental part of the investigation we were able to validate a dislocation based mechanistic model for the initiation of DRX. Additionally to the common finding of a constant mean grain size in the steady state regime we proved that the distribution also remains invariant. By this we were able to replace the empirical power law relation between steady state flow stress and grain size with the physical concept and validated the respective relations with both strain rate and temperature jump tests on two different materials. This result yields a new approach for a prediction of the steady state flow stress. One main objective of this project was to provide a deeper understanding of the experimentally observed law σ ∼ d^−1 with σ denoting the flow stress and d the average cell or subgrain size. A partial answer to this question could be given. As was shown, due to the presence of Wc , i.e. since the Cosserat model is a gradient model, upon minimisation a natural partitioning of Ω into subsets may occur where Re is (approximately) constant. Recent numerical simulations show that these analytical results carry over to 3D. Yet, the effect of softening still needs to get analyzed. We expect softening (modeled by the Avrami equation) to counteract the generation of dislocations such that an equilibrium forms.
Projektbezogene Publikationen (Auswahl)
- ’Deformation patterning in Cosserat plasticity, Modelling Simulation Mater. Sci. Eng. 21(3) 2013
T. Blesgen
(Siehe online unter https://doi.org/10.1088/0965-0393/21/3/035001)
