Experimental evaluation of the fatigue notch factor in as-built specimens produced by Wire and Arc Additive Manufacturing

Abstract

The notch Effects created by the rough surface of as-built Wire and Arc Additive Manufactured (WAAMed) products may negatively affect the fatigue resistance. This can be prevented by post-production treatments such as machining, but it implies an additional manufacturing step involving costs and time. There is a need to quantify the actual notch Effects of as-built surfaces of WAAMed parts, which can be accomplished via a parameter called fatigue notch factor. This paper focuses on the experimental evaluation of the fatigue notch factor in as-built WAAMed specimens made of AISI 308LSi stainless steel tested with a load ratio of 0.1. Two test series consisting of as-built and machined plain specimens, respectively, have been tested by applying the load perpendicularly to the deposition plane. In this loading configuration, the as-built surface can be regarded as made of periodic notches. A dedicated specimen geometry based on the indications given in the International Standard ASTM E466-21 has been used for the tests. This innovative design allows to induce crack initiation in the periodic notches of the as-built surface while preventing the final fatigue fracture at the first notch root. After the fatigue tests, the fracture surfaces resulting from some specimens have been analyzed using the Scanning Electron Microscope (SEM) to determine the location of crack initiation. As a result of the study, the S-N curves in terms of nominal stress range have been derived and the fatigue notch factor has been determined.