Estimating the fatigue thresholds of additively manufactured metallic materials with consideration of defects

The fatigue limits of defective alloys can be estimated by using classical models which require the experimental evaluation of some material properties. In the case of the Atzori-Lazzarin-Meneghetti model (ALM), the experimental fatigue limit of the "defect-free" material, Ago, and the threshold stress intensity factor for long cracks, Delta Kth,(LC), are required to evaluate the transition of the Kitagawa-Takahashi diagram, i.e. the fatigue limits of small defects. Recently, by using data taken from the literature an empirical model has been calibrated for evaluating Delta Kth,(LC) of several wrought as well as additively manufactured (AM) alloys for different load ratios (-1, 0 and 0.5), where the sole parameters required are the hardness (HV) and a properly defined micro structural lengths, l. As to the "defect-free" plain material fatigue limit, i.e., Delta sigma(0(R)), for different load ratios, the fatigue limit estimation for R = -1 (Delta sigma(0(R-1)) = f(HV)) has been corrected by using a classical mean-stress-based model. As a result, the ALM model was defined and compared with short cracks/small defects fatigue tests results taken from the literature. A good correlation has been found between theoretical estimation and experimental results obtained from the fatigue tests on defective AM alloys with R = -1 and 0.1. (C) 2021 The Authors. Published by Elsevier B.V.