PhD in Computational Materials Science

Discrete Element simulation with Level Sets for sintering

The functional and structural properties of sintered products are highly dependent on microstructure, porosity, grain size and homogeneity - themselves determined by process conditions - temperature, holding time and atmosphere - and the properties of the powders - size, grain size distribution and composition. For nano-sized powders, the challenge is to limit grain growth during sintering in order to take full advantage of the unique properties conferred by small grains in the final material.

The SIMaP laboratory has recognized expertise in simulations of sintering using the discrete element method (DEM) [1,2]. In the model, each particle interacts with its neighbors through appropriate contact laws specially designed for high temperature contacts. Local constraints and defect evolution are simulated with realistic microstructures and grain size distributions. For example, the importance of the initial stacking of particles, with its intrinsically heterogeneous structure, is explicitly taken into account.

Up to recently, particles were simply modelled as spheres. This simplifying assumption has been overcome by the implementation in our in-house code https://simap.grenoble-inp.fr/fr/equipes/animations-discrete-element-method of a Level-Set approach that authorize the use of arbitrary shapes from e.g. X-ray tomography images. This exciting development requires further work to fully address realistic sintering modeling. For example, non-convex shapes are not yet feasible. Also, grain-growth, which is a key feature of sintering should be coupled to the Level-Sets. These developments would greatly improve the usefulness of discrete element simulations for understanding sintering mechanisms. In addition, Level-Sets are well adapted for dynamic reconfiguration of the shape of particles. Since particles continuously modify their topology during sintering to minimize surface energy, the implementation of deformable Level-Sets would significantly improve the realism of simulations.

The work will be mainly numerical and will deal with the implementation of the above developments. The doctoral student will work with the in-house DEM code dp3D and use it to perform sintering simulations. The proposed doctoral thesis will integrate initial microstructures obtained from already available nanotomography images into DEM simulations as an initial condition for realistic modelling and evaluation. New nanotomography images may be included during the duration of the thesis. The PhD candidate will thus work and interact with scientists and PhD students in charge of nanotomography imaging.

[1] Martin, C. L., Schneider, L. C. R., Olmos, L., & Bouvard, D. (2006). Discrete element modeling of metallic powder sintering. Scripta Mater., 55, 425–428.

[2] Paredes-Goyes, B., Jauffres, D., Missiaen, J.-M., & Martin, C. L. (2021). Grain growth in sintering: a discrete element model on large packings. Acta Materialia, 218, 117182.