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UBC Theses and Dissertations

Mesoscale modeling of stress and strain evolution in electron beam powder bed fusion additive manufacturing (EB-PBF) Chakraborty, Asmita


Components manufactured using the Electron Beam Powder Bed Fusion (EB-PBF) Additive Manufacturing method are often prone to deformation and residual stress caused by the repeated heating, melting, solidification, and cooling that occurs during the process. The presence of residual stress can reduce the service life of the parts. An estimation of the magnitude, state, and distribution of residual stress can aid in maintaining the dimensional accuracy of the component. Although effort has been made to understand the residual stress development in EB-PBF, understanding the complicated interaction between a newly deposited powder layer and the consolidated layer is still in its infancy. In this study, a coupled thermomechanical model was built to examine the buildup of stress and inelastic strain during the layer-by-layer processing of a part at the mesoscale level. A small mesoscale domain was developed to represent a volume extracted from within a much larger component. The sub-domain dimensions were chosen to include the total thickness of four powder layers and a section of previously deposited material equivalent to approximately eight consolidated layers. The model uses a novel approach to capture the transition in material response when the material changes from powder to liquid to solid. A user-defined subroutine was developed to correctly describe the evolution of thermal strain as the material solidifies and contracts. The mesoscale model developed in this work has been used to examine different scenarios. The effect of substrate temperature, electron beam power, and scan speed on the residual stress and deformation were examined. The numerical results show that a compressive plastic strain field forms in proximity to the melt pool. The model also indicates that within the temperature range of 630 ℃ to 730 ℃, a 50 ℃ increase in substrate temperature leads to a ~21% decrease in the in-elastic strain magnitude. Within the beam power range of 740 W to 940 W, the in-elastic strain decreased by ~9% with a 100 W increase in the beam power; and a ~23% increase in the in-elastic strain was observed with a 200 mm s⁻¹ increase in the beam speed.

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