Analysis of residual stress evolution during powder bed fusionprocess of AISI 316L stainless steel with experiment and numerical modeling

The stress development behavior during an additive manufacturing process was investigated by experiments and numerical finite element models. The particular manufacturing process examined was a laser powder bed fusion of AISI 316L stainless steel. In the experiment, estimation of residual stress was done by measuring distortions of beam-shaped specimens when cutting from baseplate. Cantilever beam-shaped specimens were used for the analysis and the results were compared with simple beam-shaped specimens. The cantilever beam-shaped specimens showed pronounced bending while detaching from the baseplate, whereas the simple beam-shaped specimens showed much fewer distortions. The resulted distortions were characterized by the curvature radii which decreased significantly when the beam thickness decreased. The experimental data was analyzed and compared with analytical and proposed numerical finite element models. Both the analytical and numerical models assumed sequential additions of thermally shrank layers to estimate the residual stress state and the distortion. The analytical model considered pure elastic deformation of each layer while the numerical model assumed elastoplastic behavior. A detailed characterization of the residual deformation in the specimens through macroscopic and microstructural observations indicated that there is a significant stress relaxation by annealing effect during the process. The numerical model used in this study was able to predict the distortions and the residual stress distributions observed in the experiments. Although there was generally good correlation between the model and the experiments with the model parameters used in the study, the model assumed many significant aspects of the material and process behavior. Additional model parameter calibrations shall be required if the object shape, scanning parameters, or material properties are changed significantly.