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Although additive manufacturing (AM) has gained significant attention due to the advantages it offers and is currently a focus of much research, design of critical load carrying components utilizing such processes is still at its infancy. This is due to the fact that most of the load carrying components made by AM processes are subjected to cyclic loads, and fatigue behaviour of AM metals is far less understood as compared with those made by conventional methods, such as wrought and cast metals. To better understand the fatigue behaviour of AM metals, a wide range of issues that affect the behaviour in a synergistic manner must be considered. These include the effects of defects, residual stresses, surface finish, geometry and size, layer orientation, and heat treatment. Additionally, due to the multiaxial nature of the loading and/or complex geometries typically manufactured by AM processes, the stress state is often multiaxial including both normal and shear stresses. In this paper, the aforementioned effects influencing the fatigue resistance of AM parts, including torsion and multiaxial fatigue behaviour, are briefly discussed using some recently generated experimental data on Ti‐6Al‐4V by the authors.

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In this study, a simple approach for estimating the effect of surface roughness on the fatigue strength of additive manufactured Ti‐6Al‐4V is investigated. Surface roughness parameters are used to estimate the elastic stress concentration factor and the resulting fatigue stress concentration factor. The estimated fatigue strengths are then compared with experimentally obtained fatigue strengths for specimen batches with varying surface conditions. Results show that the estimated fatigue strengths are comparable with the experimental fatigue strengths, and the predicted stress‐life curves fit the experimental data reasonably well.