The study of critical defects in selective laser melting material under very high cycle fatigue loading

This paper focuses on the fatigue behaviour of materials produced by selective laser melting. It highlights that internal defects or structural imperfections serve as potential fatigue crack initiation sites. The role of internal imperfections of microstructure becomes more pronounced in the very high cycle fatigue regime. The study is focused on the numerical simulations of the selected laser melting process to discover the nature, shape and distribution of typical defects based on laser beam parameters and scanning strategies. The non-linear heat conductivity problem with a moving phase boundary is solved for both single and multiple laser tracks. The problem is formulated in enthalpy terms. Two primary types of defects are discovered: not-melted zones and re-melted zones. These types of defects are simulated in the computer aided model of a very high cycle fatigue specimen. The not-melted zones are associated with localized regions of reduced elastic modulus, whereas the re-melted zones are associated with regions of slightly elevated values of elastic modulus. Fatigue life predictions, performed using multi regime fatigue fracture model, show a significant difference in fatigue life between specimens containing not-melted and re-melted defects. Under identical loading condition, the fatigue life of specimen with not-melted defects is about 10 times shorter compared to homogeneous material.