Thermo-mechanical simulation of L-PBF process at part-scale by coupling grain structure calculation and crystal viscoplasticity

Overview & Synopsis

An integrated numerical framework is proposed to perform a thermomechanical analysis of Laser Powder Bed Fusion (L-PBF) at the part scale, covering the entire construction process. The novelty lies in the fact that the thermomechanical analysis is driven by the evolving grain structure, also predicted at the part scale. The grain structure is first generated using a hybrid - Cellular Automaton (CA) method, which enables the generation of the grain structure on a CA grid at part-scale while incorporating the detailed scanning trajectories. For the thermo-mechanical simulation, a layer-by-layer thermal analysis includes the non-exposed powder, whereas the mechanical analysis only considers the substrate and the part under construction. A crystal plasticity model is employed for the nickel-based superalloy Inconel 718 (IN718), utilizing the CA grain structure referenced by Euler angles. A reduced grain approach is proposed, wherein Euler angles from the CA grid are projected onto the mechanical mesh. The mechanical mesh size is chosen appropriately to balance computational efficiency and accuracy. The calibration of the parameters of the crystal plasticity laws is conducted from room temperature up to 1100 C using tests performed on homogenized IN718 material. Tensile tests on the representative volume elements (RVEs) of grain structures with different laser scanning trajectories are performed to study the mechanical response for each specified texture. Finally, thermo-mechanical simulations are applied to the L-PBF construction of a propeller with single-crystal and polycrystalline grain structures. At each time increment, the temperature field is transferred to the mechanical mesh, and grains are activated according to the part under construction. The influence of local grain texture on anisotropic stress distribution and distortion is analyzed and discussed.