Predicting the interfaces between fatigue crack growth regimes in 7150-T651 aluminium alloy using the fatigue damage map S.A. Curtis a , J. Solis Romero a , E.R. de los Rios a , C.A. Rodopoulos a, , A. Levers b a Department of Mechanical Engineering, Structural Integrity Research Institute of the University of Sheffield University (SIRIUS), University of Sheffield, Sheffield S1 3JD, UK b Airbus UK, Chester Road, Broughton, Chester CH4 0DR, UK Received 10 August 2001; received in revised form 14 May 2002 Abstract The fatigue damage map (FDM) is used to establish the domains of different crack growth regimes including microstructural dependent (short), microstructural independent (long) and non-propagating cracks. The FDM is applied over a wide range of applied stresses to determine the extent of each domain from crack instability to crack arrest. Two important boundaries of the FDM are examined in this paper */the crack arrest curve and the transition from short to long crack growth. The accuracy of the model predictions are evaluated through crack arrest experiments and fractographic examination of failure cracks. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Aluminium alloy; Fatigue damage map; Fatigue cracks 1. Introduction The growth of microstructurally dependent (MD) fatigue cracks has been a field of much concern in fatigue research for more than two decades [1,2]. Unfortunately, recognition of the role of MD fatigue cracks on the residual strength of aircraft structures, especially in the case of multiple site damage (MSD), came in 1988 after the Aloha 737 accident in Hawaii. Today the behaviour of short cracks is in the forefront of aeronautical fatigue research. The idea of a fatigue damage map was first introduced by Brown [3] who determined the interfaces between short, long and non-propagating cracks of a 0.4 wt.% C steel. This work was based on empirical modelling of fatigue crack growth in the microstructural crack growth (MCG) and elasto-plastic fracture mechanics (EPFM) regimes [4]. The concept of a fatigue damage map was later put into a more theoretical framework by Navarro and de los Rios who derived the conditions for crack arrest and crack instability from a physical based model of crack propagation [5]. In this model, the driving force for crack propagation is the crack tip plastic displacement (CTPD) the magnitude of which depends on the size of the crack tip plastic zone (CTPZ). The CTPZ is assumed to be constrained by microstructural features such as grain and phase boundaries [6]. According to the above, the crack arrests when the stress intensity ahead of the plastic zone is unable to overcome the constraint. In practical terms it means that the magnitude of the applied stress is below the fatigue limit at short crack lengths and below the threshold for crack propagation (Kitagawa  /Takahashi limit) at longer crack lengths. Similarly, the crack is assumed to reach instability when the combined effect of the material resistance, i.e. grain boundary constraint and resistance to crack tip plastic flow are unable to counteract the increasing crack tip stress intensity. In practical terms, it means that the stress-crack system produces general yielding or that the fracture toughness of the material is reached [5]. In [7] the FDM was extended to cover the conditions that characterised the transition from short to long crack growth considering changes in the number of slip  Corresponding author. Tel.:  /44-114-227-710; fax:  /44-114-222- 7890 E-mail address: c.rodopoulos@sheffield.ac.uk (C.A. Rodopoulos). Materials Science and Engineering A344 (2003) 79  /85 www.elsevier.com/locate/msea 0921-5093/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0921-5093(02)00416-1