Numerical investigation of residual stresses in thin-walled additively manufactured structures from selective laser melting

Selective laser melting (SLM), a metal laser powder bed fusion additive manufacturing method, involves several cycles of very high temperature gradient heating and cooling during the solidification of each layer, which can cause the accumulation of detrimental residual stresses in the 3D printed structure. This work uses a thermo-mechanical computational modeling approach to investigate the formation of residual stresses in thin-walled structures and also investigates the effects of varying taper on the evolution of residual stress profiles of the build. Three material grades; namely, Titanium alloy (Ti64), Stainless steel (SS316L) and Inconel (IN718) have been used for this study. The results show that varying taper thickness up to a certain value has a considerable effect on residual stress evolutions in thin-wall structures, however, beyond a certain value of the taper level, the residual stresses are observed to converge. Also, it is observed that the tensile stresses at the edges of the wall are almost equal or exceed the yield stress of the materials. Among the three material grades considered, the magnitude of residual stress was higher in Ti64 and the stresses are dominant in the build direction. The simulation framework is also applied to analyze the effect of residual stresses on the mechanical properties of complex thin-wall structures such as TPMS (Triply Periodic Minimum Surfaces) lattice structure, using Schwarz Primitive (SP) as a case study. It is observed that the residual stresses lower the effective elastic properties of the lattice structures by 6% ∼ 10% for the three material grades but has no effect on the effective plastic behavior of the material.