ORIGINAL CONTRIBUTION Fatigue life prediction of additively manufactured material: Effects of surface roughness, defect size, and shape A. Yadollahi 1 | M.J. Mahtabi 2 | A. Khalili 3 | H.R. Doude 2 | J.C. Newman Jr 4 1 Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Starkville, MS 39762, USA 2 Dynamic and Smart Systems Laboratory, Mechanical, Industrial and Manufacturing Engineering Department, The University of Toledo, Toledo, OH 43606, USA 3 Structural Engineer, Pure Technologies, Branchburg, NJ 08876, USA 4 Department of Aerospace Engineering, Mississippi State University, Starkville, MS 39762, USA Correspondence A. Yadollahi. Email: aref.yadollahi@gmail.com Abstract In this paper, the effects of process‐induced voids and surface roughness on the fatigue life of an additively manufactured material are investigated using a crack closure‐based fatigue crack growth model. Among different sources of damage under cyclic loadings, fatigue because of cracks originated from voids and surface discontinuities is the most life‐limiting failure mechanism in the parts fabricated via powder‐based metal additive manufacturing (AM). Hence, having the ability to predict the fatigue behaviour of AM materials based on the void features and surface texture would be the first step towards improving the reliability of AM parts. Test results from the literature on Inconel 718 fabri- cated via a laser powder bed fusion (L‐PBF) method are analysed herein to model the fatigue behaviour based on the crack growth from semicircular/ellip- tical surface flaws. The fatigue life variations in the specimens with machined and as‐built surface finishes are captured using the characteristics of voids and surface profile, respectively. The results indicate that knowing the statisti- cal range of defect size and shape along with a proper fatigue analysis approach provides the opportunity of predicting the scatter in the fatigue life of AM mate- rials. In addition, maximum valley depth of the surface profile can be used as an appropriate parameter for the fatigue life prediction of AM materials in their as‐ built surface condition. KEYWORDS additive manufacturing, crack growth, FASTRAN, fatigue life prediction, laser powder bed fusion Nomenclature: a, Crack depth, μm; a i , Initial crack depth, μm; B, Thickness of crack growth specimens, mm; C, Crack half‐length intersecting the free surface, μm; c i , Initial crack half‐length, μm; E, Modulus of elasticity, GPa; F, Stress intensity boundary correction factor; m, Fracture toughness ductility parameter; K, Stress intensity factor, MPa√m; K Ie , Elastic stress intensity factor at failure, MPa√m; K T , Stress concentration factor; K F , Elastic‐plastic fracture toughness, MPa√m; K max , Maximum stress intensity factor, MPa√m; da/dN, Crack growth rate, m/cycle; R, Stress ratio; R a , Surface roughness, μm; R t , Maximum profile height, μm; R v , Maximum valley depth, μm; S o , Crack‐opening stress from crack closure model, MPa; S max , Maximum applied remote stress, MPa; S min , Minimum applied remote stress, MPa; S n , Net‐section stress at failure, MPa; W, Width of crack growth specimens, mm; α, Constraint factor; ϕ, Parametric angle for surface crack, deg.; σ ut , Ultimate tensile strength, MPa; σ ys , Yield stress, MPa; ΔK, Stress intensity factor range, MPa√m; ΔK eff , Effective stress intensity factor range, MPa√m. Glossary: 3D, Three‐dimensional; AM, Additive manufacturing; AR, Aspect ratio; CP, Compression precracking; CT, Computed tomography; C(T), Compact tension; EIFS, Equivalent initial flaw size; H, Horizontally built; HCF, High cycle fatigue; HIP, Hot isostatic pressing; LCF, Low cycle fatigue; L‐PBF, Laser powder bed fusion; LSG, Low stress ground; RIFS, Real initial flaw size; TPFC, Two‐parameter fracture criterion; V, Vertically built Received: 4 December 2017 Revised: 8 February 2018 Accepted: 11 February 2018 DOI: 10.1111/ffe.12799 Fatigue Fract Eng Mater Struct. 2018;1–13. © 2018 Wiley Publishing Ltd. wileyonlinelibrary.com/journal/ffe 1