Marcus Jainta

Calibration of a multi-phase field model with quantitative angle measurement

Over the last years, the phase-field method has been established to model capillarity-induced microstructural evolution in various material systems. Several phase-field models were introduced and different studies proved that the microstructure evolution is crucially affected by the triple junction (TJ’s) mobilities as well as the evolution of the dihedral angles. In order to understand basic mechanisms in multi-phase systems, we are interested in the time evolution of TJ’s, especially in the contact angles in these regions. Since the considered multi-phase systems consist of a high number of grains, it is not feasible to measure the angles at all TJ’s by hand. In this work, we present a method enabling the localization of TJ’s and the measurement of dihedral contact angles in the diffuse interface inherent in the phase-field model. Based on this contact angle measurement method, we show how to calibrate the phase-field model in order to satisfy Young’s law for different contact angles.

Massively parallel phase-field simulations for ternary eutectic directional solidification

Microstructures forming during ternary eutectic directional solidification processes have significant influence on the macroscopic mechanical properties of metal alloys. For a realistic simulation, we use the well established thermodynamically consistent phase-field method and improve it with a new grand potential formulation to couple the concentration evolution. This extension is very compute intensive due to a temperature dependent diffusive concentration. We significantly extend previous simulations that have used simpler phase-field models or were performed on smaller domain sizes. The new method has been implemented within the massively parallel HPC framework waLBerla that is designed to exploit current supercomputers efficiently. We apply various optimization techniques, including buffering techniques, explicit SIMD kernel vectorization, and communication hiding. Simulations utilizing up to 262,144 cores have been run on three different supercomputing architectures and weak scalability results are shown. Additionally, a hierarchical, mesh-based data reduction strategy is developed to keep the I/O problem manageable at scale.

Application of Large-Scale Phase-Field Simulations in the Context of High-Performance Computing

In material science, simulations became a common tool for the understanding of the underlying behaviour of different classes of materials. Due to the growing complexity of problems at hand, the simulation domains, and therefore the computational effort is steadily increasing. We presents various application of the phase-field method; ranging from the solidification of ternary eutectics and pure ice systems to the interaction of multiple liquid phases on fibers. All these topics have in common, that they need a large number of cores to investigate the decisive physical effects in adequate time. We show an overview of the results for this wide range of applications and the scaling behaviour of the used software frameworks.

Phase-field simulations of large-scale microstructures by integrated parallel algorithms

In this report, we present specific model extensions of the phase-field method [17] implemented in the software framework PACE3D and summarize the underlying parallelized algorithms. Three different applications of microstructure evolution processes are illustrated and the need of large representative volume elements and of efficient parallelization. Within a first application, a parallel connected component labeling algorithm, is optimized for a large number of computing units, and is used for the simulation of pore development in the sintering processes. The second topic discusses a brute force study of the Read-Shockley model, to investigate recrystallization and abnormal grain growth in anisotropic polycrystalline material systems. The third topic is focussed on heat transfer and fluid flow in metallic foam structures depending on the porosity as base material for new heat storage systems.