SPP 1713: Strongly coupled thermo-chemical and thermo-mechanical states in applied materials
The objective of the overall program is to establish a new paradigm of physics-based material modeling that integrates the influence of process history and external chemical-mechanical loading and is applicable to optimize the production, properties, and lifetime of applied materials for a sustainable economy. This will be demonstrated on two technologically important classes of materials, metals and polymers. Cross-fertilization of the different approaches and material models used is also envisaged.
Individual sub-objectives of an overarching nature are:
- To demonstrate the superiority and technological potential of coupled thermo-chemical and thermo-mechanical modeling for key metallic and polymeric materials.
- To develop physically based material models with full coupling between chemistry and mechanics, taking into account the process history.
- Develop comprehensive computational tools by bringing together the expertise of different communities: Materials, Thermodynamics, Mechanics, Metals and Polymers.
- Integrate experimenters and simulation software developers to combine the best data with the best models and the best numerical techniques.
- To bring together the scientific communities from computational thermodynamics, continuum mechanics and materials science
TP M4: Modeling of bainitic transformation during press hardening
In the M4 project, which was carried out by IWT in cooperation with RWTH Aachen University and FZ Jülich, the chemo-mechanical coupling during bainitic press hardening was investigated on all relevant length scales both experimentally and theoretically and by means of simulations. Specific sub-objectives in the course of the project were:
- Investigation of the interplay between plastic deformation, external stresses, interfacial kinetics, precipitation formation and their influence on bainitic transformation.
- Linking the descriptions on microscopic, mesoscopic and macroscopic scales and interpreting them from the point of view of a consistent thermodynamic description.
The quantitative description of microstructure evolution in bainitic press hardening requires the development of novel modeling techniques to correctly capture the interplay of phase transformation kinetics and thermodynamics, elastic and plastic deformations, and chemical effects in the relevant alloys. They provide a basis for understanding phase transformation kinetics with full consideration of thermo-chemo-mechanical coupling at all length scales. Key results here are:
- Ab initio methods can be used at the lowest scale for parameter-free prediction of elastic parameters with an extension to large deformations. The scale-bridging comparison with classical density functional theory and phase-field crystal methods provides a fundamental understanding and quantitative analytical description of stress-strain relationships that can serve as the basis for higher-scale microstructure evolution modeling.
- The in-depth analyses of EBSD measured microstructure data on the crystallography of bainitic transformation allow us to extract mathematical descriptions of transformation plasticity as a result of orientation variant selection by applied stresses. In addition, the mechanisms of variant selection central to the formulation of mesoscopic descriptions have been determined.
- Proximity to interfaces, e.g., ferrite-austenite interfaces or grain boundaries, can influence the local thermodynamics of carbide precipitation via an elastic interaction. We have shown how these scale bridging effects can be effectively formulated to exploit the equilibrium properties and precipitation kinetics of carbides near surfaces and interfaces under the influence of external and internal stresses.
- Thermodynamically consistent phase field descriptions using nondiagonal interactions allow the descriptions to be quantitatively and consistently linked to sharp interfacial models even in the presence of finite diffusion contrasts in the phases.