Numerical estimation of the effects of microcavities on the plastic zone size ahead of the crack tip in aluminum alloy 2024 T3 B. Bachir Bouiadjra a, * , M. Elmeguenni a,b , M. Benguediab a , M. Belhouari a , M. Nait-Abdelaziz b a LMPM, Department of Mechanical engineering, University of Sidi Bel Abbes, BP 89, Cité Ben M’hidi, Sidi Bel Abbes, 22000, Algeria b Laboratoire de Mécanique de Lille (UMR CNRS 8107), USTL, Polytech’Lille, Avenue P. Langevin, 59655 Villeneuve d’Ascq Cedex, France article info Article history: Received 23 July 2007 Accepted 8 May 2008 Available online 17 May 2008 Keywords: Crack Microcavity Plastic zone FEM Plastic strain Stresses abstract In this study the non-linear finite element method is used to analyse the effect of presence of microcavity near a crack tip on the variation of the shape and the size of the plastic zone ahead of the crack tip in the case of confined plasticity. The FE Code Franc2D/L is used to carry out this objective. The effect of the interdistance crack tip-microcavity on the plastic zone size is highlighted. The obtained results show that the presence of the microcavity affects in very significant way the shape and the size of the crack plastic zone. The relative distance between the crack tip and the microcavity has a very important effect on the size of the confined plastic zone. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction It is commonly understood that fracture behaviour of ductile material depends on the plastic deformation created ahead of the crack tip. In understanding of fatigue properties of metallic alloys, of out most important is the precise characterization of the plastic deformation of the materials in the vicinity of the crack tip. The plastic behaviour near the tip of stationary crack in engineering materials has been intensively studied using classical plasticity theory based on the Von-Mises yield criterion and the associative flow rules [1–6]. The fatigue process and its mechanism are largely influenced by the presence of micro-defects that are inherent to the materials such as microcavities. The growth behaviour of a fatigue crack is a consequence of plastic deformation accommodated at its tip during the loading [7]. Thus, FCG rates should be analysed in terms of a parameter, which bears a relation to the appropriate mechanism of crack growth. In the literature, elastic–plastic fracture mechanics was the basis of different parameters developed and applied to charac- terise FCG behaviour in different crack regimes [8]. However, dif- ferent models have been proposed to predict the notch FCG behaviour in the three regimes of micro-structurally short, physi- cal short (PSC) and long cracks. Corresponding analyses were based on some strain intensity factors, J-integral, surface strain redistri- bution, crack tip plasticity and the interaction between notch and crack tip plasticity. The extent of the crack tip plastically de- formed zone was invoked to correlate the opening mode FCG [7]. This is not expected to work in cases where crack tip plastic zone can be large in relation to the crack length, e.g. short cracks in unnotched components. A study of interaction between cracks and micro defects in thin plate is important in providing a good understanding of mechani- cal behaviour of structures with defects and is helpful to the mate- rial and structural design. This type of problems has been studied by many authors [9–17]. Notice that most authors considered an elastic behaviour of materials. When cracks are analyzed, the behaviour of the material ahead of the crack tip is considered iso- tropic, i.e., plastic deformation occurs identically in all directions and there are no preferred directions for the plastic deformation. In this case, the plastic deformation can be mathematically formu- lated with the help of classical isotropic plasticity. This situation significantly differs when the crack tip is near a micro-defect, the plastic zone ahead of the crack tip is considered anisotropic. The aim of this study is to analyze the effect of presence of mi- cro cavity on the shape and size of the plastic zone ahead of the crack tip using the finite element method for the case of small scale plasticity. This case was selected because a microcavity cannot af- fect the plastic zone in large plastic deformation. Three configura- tions related to the position of the micro defect are analyzed (a) Microcavity in the prolongation of the crack tip. (b) Microcavity shifted perpendicularly to the crack. (c) Two microcavities located on both sides of the crack tips. 0261-3069/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2008.05.021 * Corresponding author. Tel./fax: +21348544100. E-mail address: bachirbou@yahoo.fr (B. Bachir Bouiadjra). Materials and Design 30 (2009) 752–757 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes