The effect of surface finish on tensile behavior of additively manufactured tensile bars

Additive Manufacturing (AM) has significantly increased the design freedom available for metal parts. Many novel designs rely on the existence of surfaces that are not accessible and therefore rely on the surface finish of the parts directly from the AM equipment. Work has been performed to characterize the difference between AM, then machined tensile samples and AM tensile samples with an unimproved surface finish. This work utilizes surface analysis, fractography, and finite element analysis (FEA) to expand on this by investigating the effects of the unimproved surfaces on local tensile behavior and fracture mechanics in AM materials. Results show that measurement error in cross-sectional area is the main source of variation between unfinished and machined strength measurements. Results also indicate that a ductile material may demonstrate the same tensile strength regardless of post processing. Fractography shows that stress concentration near the surface of the samples leads to changes in fracture behavior likely explaining the difference in elongation of the samples. Finally, FEA work did not successfully show a difference in fracture initiation, though this is likely due to inaccurate representation of the samples surface.