Fracture Toughness Testing of 316L Steel Manufactured by Laser Powder Bed Fusion

Abstract

Laser Powder Bed Fusion (LPBF) is a relatively new manufacturing technique that offers many benefits. However, the utilization of selective laser melting (SLM) manufactured components depends on the assurance of their integrity during operation. Samples manufactured through LPBF are prone to defects. Therefore, it is important to determine the fracture toughness of the materials. In this work, fracture toughness tests on single edge notched bend (SENB) samples have been performed and the results are presented. The samples have been manufactured in 3 orthogonal directions enabling the influence of defect orientation relative to the build direction on toughness to be determined. The crack growth has been monitored using both elastic compliance and the potential drop (PD) technique, and the crack tip strain fields have been imaged using digital image correlation techniques. It has been found that the toughness of samples with the crack plane parallel to the build layers (vertical) is greater than that of samples with the crack plane normal to the build layers (horizontal), contrary to expectations based on previous research. This behavior is likely to be a result of changes in porosity ahead of the crack tip due to inadvertent cooling effects during the build process, resulting in fewer build defects ahead of the crack tip in the “vertical” samples.