Project Details
Projekt
Multiscale thermoplastic analysis in the solidification zone
Subject Area
Mechanics
Joining and Separation Technology
Joining and Separation Technology
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 434946896
The aim of the planned research project is the further development of the multi-scale modeling approach to identify micromechanical effects that lead to the initiation of solidification cracks during laser beam welding. One main aspect is the analysis of the material stability on subareas of the microscale, which is carried out by means of an accompanying localization analysis. A loss of material stability is associated with the loss of rank-1 convexity and is based on an acoustic tensor that is not strictly positively definite. Evidence-based analysis is carried out on representative sections of the microscale, which, as a first working hypothesis, have at least a 90 percent share of solidified material. The subareas of the microscale to be investigated are initially based on simplified dendrite structures, in the sense of statistically similar representative volume elements, and are extended by microstructures obtained by high-resolution phase field simulations from TP6. High-resolution HPC simulations with integrated localization analysis are made possible in cooperation with TP5. The microstructural model serves as the basis of the homogenization scheme for implementing the multiscale approach. The coupling of the scales is implemented for mechanical and thermal variables using established approaches to describe the scale transitions. In addition, the material model is extended to an incremental variational formulation of finite thermoplasticity, which automatically leads to symmetric algebraic structures. The resulting symmetry of the equation systems is to be explicitly exploited in the numerical implementation within the framework of high-performance computing (HPC). This will be done in a specifically coordinated co-design with TP5. In addition, the extension of the FE^2 homogenization method in the FE2TI software package will be pursued in close cooperation. Operator split techniques based on isothermal and isentropic assumptions will be considered, which exploit the symmetry properties of the decoupled equation systems and enable improved time step width control by considering different time scales in the thermal and mechanical problem. Together with all sub-projects of the research group, this sub-project is dedicated to analyzing various indicators for the formation of solidification cracks. In particular, the local stability analysis on the microscale is considered as an indicator of the instability associated with crack formation and compared with other approaches in selected benchmark simulations of laser beam welding. The understanding of the relationship between the process parameters and mechanisms of solidification cracking developed in this way represents a key, overarching objective of the research group.
DFG Programme
Research Units
