Advanced Materials Research Vol 1099 (2015) pp 1-8 http://dx.doi.org/10.4028/www.scientific.net/AMR.1099.1 Fatigue behavior of aerospace Al-Cu, Al-Li and Al-Mg-Si sheet alloys Nikolaos D. Alexopoulos 1, a , Vangelis Migklis 1, b , Stavros K. Kourkoulis 2,c and Zaira Marioli-Riga 3,d 1 Department of Financial Engineering, University of the Aegean, 41 Kountouriotou str, 82100, Chios, Greece 2 National Technical University of Athens, Department of Mechanics, Laboratory of Testing and Materials, 5 Heroes of Polytechnion Ave., 15773 Athens, Greece 3 Hellenic Aerospace Industry, Research and Development Department, 32009 Schimatari, Greece a nalexop@aegean.gr, b vaggelis.migklis@gmail.com, c stakkour@central.ntua.gr, d zmarioli@haicorp.com Keywords: Abstract In the present work, an experimental study was performed to characterize and analyze the tensile and constant amplitude fatigue mechanical behavior of several aluminum alloys, namely 2024 (Al-Cu), 2198 (Al-Li) and 6156 (Al-Mg-Si). Al-Li alloy was found to be superior of 2024 in the high cycle fatigue and fatigue endurance limit regimes, especially when considering specific mechanical properties. Alloy 6156 was found to have superior constant amplitude fatigue performance that the respective 6xxx series alloys; more than 15% higher endurance limit was noticed against 6061 and almost 30% higher than 6082. Alloy 6156 presented only a marginal increase in fatigue life for the HCF regime. Introduction It is well known that fatigue is the most important design parameter when designing airframes and this is the main reason for selecting the proper engineering material for the perfect location of the aircraft. For many decades now, the most damage tolerant aluminum alloy is the Al-Cu 2024-T3 that is widely used in the wings and barrel sections. During the last decade, an effort has been assessed to replace the “traditional” 2024 sheets with innovative 2198 made from innovative, third generation Al-Li alloys [1]. The second generation of Al-Li alloys showed that these alloys have great damage tolerance potential and their next generation has the additional advantage to be efficiently welded, thus trying to make the traditional riveting process obsolete [2]. Aluminum alloys from the 6xxx series, e.g. 6056 were selected in belly fuselage sections where strength and damage-tolerance properties are required. However, future metallic airframes may contain laser beam welded structures to achieve lightweight integral airframes. Innovative 6156 fuselage sheets are particularly recommended for such a use as it is supposed to have higher damage tolerance capabilities than its predecessor [3]. So far the literature review on the aluminum alloy 6156 remains very limited; the effect of aging treatments on microstructure and hardness are reported in the literature [4-6] as well as the effects of Ag addition on the long thermal stability of the alloy [7]. The high cycle fatigue performance [8] as well as the quench sensitivity of toughness [9], [10] are probably the only articles in the open literature regarding the mechanical properties of this innovative aluminum alloy. To this end, the authors of the article suggested to compare the innovative Al-Mg-Si sheet alloy with the traditional alloys from the same alloy series, e.g. 6061 and 6082. This article will provide experimental test data on tensile and fatigue properties of the innovative 2198 and 6156 sheet aluminum alloys; though the direct comparison of alloys from different aluminum alloy series (e.g. 2xxx and 6xxx) does not reflect the true potential of the alloys by taking into account the individual characteristics of each aluminum series, nevertheless a