Bending Fatigue in Additively Manufactured Metals: A Review on Current Research and Future Directions

Metal additive manufacturing (MAM), also referred to as 3D printing, has proved remarkable in the fabrication of complex metal components in multiple sectors. But the assessment of this revolutionary process through bending fatigue is frequently impeded due to concerns about mechanical and physical conditions of the printed components. The unique layer-by-layer production process results in varied microstructures, anisotropy, and intrinsic defects that considerably differ from traditionally manufactured wrought metals. This review article aims to integrate and evaluate historical and contemporary research on the bending fatigue of additively manufactured materials. More specifically, the impact of process parameters, build orientation, surface conditions, and post processing techniques such as machining, surface treatments, and polishing on bending fatigue performance are summarized. Adopting prediction methodologies were emphasized to facilitate flaw detection and thereby ensuring the safe and reliable deployment of AM parts in dynamic load carrying applications. Some future research directions were proposed, including the i) Development of Standardized specimens and test protocols, ii) adaptation to miniaturization to overcome challenges in high throughput fatigue testing, iii) application of emerging geometries such as the Krouse specimen for mechanistic investigations, and iv) Possibility of developing correlation across different testing methods and materials to reduce experimental burden. By synthesizing the recent progresses and identifying unresolved challenges, this review outlines an organized and clear pathway towards future research for the deployment of advanced bending fatigue characterization in AM process. The novel idea of adapting miniaturized Krouse geometries in bending fatigue test of additively manufactured metals is a viable prospect for the feasible fabrication of AM fatigue coupons with reduced specimen preparation defects and enhanced fatigue strength.