Effects of notch-load interactions on the mechanical performance of 3D printed tool steel 18Ni300

Abstract

The capability of additive manufacturing to produce parts with complicated geometrical features is one of the unique advantages of this technology over traditional production methods. However, the intricate interaction between concentrated stress fields imposed by various geometrical profiles, inherent defects, and external loads must be comprehensively recognized to leverage the aforementioned ability. Consequently, this study investigated the simultaneous effects of macroscopic notches and microscale defects on the performance of tool steel 18Ni300 under quasi-static and cyclic loading regimes. The specimens were manufactured using the laser-powder bed fusion technique, a common method for industrial applications that rely on metals. Eleven (horizontally built) sample designs, consisting of external or internal notches with different characteristics, were considered in this study to ensure a comprehensive comparison. The results showed that the surface quality was slightly higher along the notch roots than in the other areas. All the notches, regardless of their types, reduced ductility. Notch strengthening was generally observed in the notched samples under quasi-static loads. However, the degree of strengthening was directly related to the stress concentration factor, unlike for typical conventional metals. This unexpected behavior was attributed to the inherent defects in the manufacturing process. The surface defects at the notch roots played a dominant role in governing fatigue failures. A modification of the Murakami approach was proposed to estimate the fatigue life of notched components fabricated via additive manufacturing. Finally, the applicability of the Solberg–Berto diagram to predict the failure locations in horizontally manufactured samples was evaluated. The diagram largely agreed with the experimental data obtained from this study.