Abstract
Martensitic transformation is simulated in terms of computational micromechanics applying the finite-element method in order to study the effect of microstress and microstrain causing the unusual material behavior associated with stress-assisted martensitic transformation (MT). Both the preferred orientation of martensitic crystallographic variants (orientation effect) and microplastic deformation (accomodation effect) may lead to significant macroscopic deformations (transformation-induced plasticity, TRIP). The essential microstructural features of MT are described by stress-free transformation tensors ε T,J for martensitic variants emerging along habit plane variants j. Transformation-induced microstress and accomodation strain fields are analysed for inclusion-type, plate-shaped martensitic variants transforming within a representative volume element (RVE) under different levels of externally applied stress. The RVE is specified with respect to an average Schmid-factor for the transformation shear γ. The second homogenization step is carried out by a microfield approach coupling the RVEs with antisymmetric boundary conditions. In order to describe the thermodynamic state of the stressed phases we persue a thermodynamic field concept by introducing a thermomechanical potential applicable for martensitic transformation with plasticity effects. Transformation criteria for stress-assisted nucleation and stress-driven growth enable to clarify the role of plastic deformation arising from the progress of transformation. It will be shown that the hydrostatic microstress fields developing at the plate ends of transforming martensitic crystals alter the stress-assisted nucleation characteristics. Microplastic strain stabilizes the austenite thermodynamically. The applied modelling technique also allows to study the coupling between orientation- and accommodation effect. A incremental formulation ε TP for TRIP will be discussed compared to existing relations.
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