Issue 38

X. Yu et alii, Frattura ed Integrità Strutturale, 38 (2016) 148-154; DOI: 10.3221/IGF-ESIS.38.20 148 Focussed on Multiaxial Fatigue and Fracture Fatigue crack growth of aluminium alloy 7075-T651 under non-proportional mixed mode I and II loads Xiaobo Yu Aerospace Division, Defence Science and Technology Group, 506 Lorimer Street, Fishermans Bend, VIC 3207, Australia xiaobo.yu@dsto.defence.gov.au , http://www.dsto.defence.gov.au Ling Li, Gwénaëlle Proust School of Civil Engineering, Faculty of Engineering & IT, the University of Sydney, NSW 2006, Australia lili1626@uni.sydney.edu.au , gwenaelle.proust@sydney.edu.au A BSTRACT . This study aims to investigate fatigue growth behaviour in AA7075-T651 under non-proportional mixed mode I and II loads. Fatigue tests were performed under cyclic tension and torsion using a thin-walled tubular specimen with a key-hole style crack starter. After the generation of a single-side mode I pre-crack, varied forms of mixed mode loads were applied, which in most cases led to a short distance coplanar growth followed by a long and stable crack path deviation. It was found that under most of the non-proportional mixed mode load cases, the direction of the deviated crack path could not be reasonably predicted using the commonly accepted maximum tangential stress criterion. Meanwhile, in some cases, the crack path directions could be approximately predicted using the maximum shear stress criterion. It was also confirmed for the first time that a long, stable and non- coplanar shear mode fatigue crack growth could be produced in AA7075- T651 under non-proportional mixed mode I and II loads. ©2016 Commonwealth of Australia K EYWORDS . Fatigue crack growth; Non-proportional; Mixed mode; Aluminium alloy; 7075-T651. Citation: Yu, X., Li, L. Proust, G., Fatigue crack growth of aluminium alloy 7075-T651 under non-proportional mixed mode I and II loads, Frattura ed Integrità Strutturale, 38 (2016) 148-154. Received: 12.05.2016 Accepted: 15.06.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION atigue of aircraft structures is traditionally managed based on the assumption of uniaxial loads. This is a simplified and acceptable approach for most fatigue critical locations where the local stress field is predominantly uniaxial due to loading path restrictions. Nevertheless, as evidenced in recent durability analysis of a new type of F