۱٫ Introduction

۲٫ Important factors to consider in fatigue design with AM

۳٫ Multiaxial fatigue characterization

۴٫ Summary and perspective for future research

Acknowledgements

References

Additive manufacturing (AM) is a state of the art technology enabling fabrication of complex geometries, in addition to providing other advantages as compared to the traditional subtractive manufacturing methods. However, a wide variety of factors significantly influence fatigue behavior and structural performance of components made of AM metals. In addition to the fabrication process parameters, these include the effects of build direction, surface roughness, residual stresses, and heat treatment, and multiaxial stress states. At the microstructural level, defects such as pores and lack of fusion particles, as well as other microstructural features affect the behavior. In this paper, first a brief review of the aforementioned factors affecting the fatigue behavior will be presented. Then some experimental multiaxial fatigue data for selective laser melting (SLM), which is a powder bed fusion (PBF) metal AM process, of a common Ti alloy (Ti-6Al-4V) with applications in many industries are presented and discussed. The effects of surface finish, heat treatment, and stress state will be evaluated, as well as failure mechanisms in different life regimes and the role of defects. Finally, some additional factors that must be considered before wide acceptance of the AM technology in critical load bearing applications will be addressed.

Introduction

Additive Manufacturing (AM) is a state of the art process which enables fabrication of complex geometries and provides several advantages over the traditional subtractive manufacturing methods. Among the advantages of AM process is the possibility of fabricating complicated geometries which are difficult or impossible to build using traditional manufacturing. In contrast to subtractive manufacturing, in which a part is made by removing the material from a block, in AM the part is built with a close to final shape geometry with little or no need for material removal, therefore, there is much less material waste. On site fabrication is amongst the other advantages of AM technique. AM metallic parts are commonly fabricated via Powder Bed Fusion (PBF) and Directed Energy Deposition (DED) processes. In PBF, a metal powder is melted selectively via laser or electron beam over the previous layer, while in DED, both energy source which could be laser or electron beam, and the material which is powder or wire infuse simultaneously. For more information about the fabrication process of AM parts the reader is referred to review articles in the literature, for example to [1, 2]. Several process parameters such as laser power, scanning speed and strategy, and layer thickness are amongst the important parameters which could directly influence the material microstructure and, therefore, behavior.