ICAMS / Interdisciplinary Centre for Advanced Materials Simulation
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Constitutive model developing for bcc-iron based on atomistic analysis

Date: 27.08.2012
Place: Dislocations 2012, Budapest, Hungary

Aenne Köster
Anxin Ma
Alexander Hartmaier

The glide of screw dislocations with non-planar cores dominates the plastic deformation behavior in body centered cubic iron. This yields to a strong strain rate and temperature dependence of the flow stress, the breakdown of Schimd’s law and the dependence of the dislocation mobility on stress components that do not contribute to the mechanical driving force of the dislocation glide. A constitutive model in the framework of crystal plasticity was developed, which takes all these effects into consideration. The constitutive model is based on molecular statics simulations using a semi-empirical potential. The atomistic studies yielded to quantitative relations between the local stress tensor components and the dislocation mobility. The studies reveal that not only shear stresses parallel and perpendicular to the glide direction, but also tension and compression perpendicular to the glide plane influence the dislocation core and thus change the resistance to dislocation glide. The results from the atomistic studies were incorporated to the crystal plasticity model via an extended yield rule. Together with experimental data from the literature and an optimization procedure the remaining model parameters for the crystal plasticity model were determined. The developed multiscale model is validated by comparing numerical single crystal tension tests to equivalent data with respect to orientation, temperature and strain rate dependence. Finally, the numerical calculations of bcc single crystal confirm the atomistic and recent experimental results: Glide of screw dislocation in bcc iron takes place on the {110} glide systems. By exclusively using these glide systems and the extended yield rule it is possible to model the plastic behavior of a bcc single crystal in a proper way.

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