International Journal of Fatigue 25 (2003) 949–954 www.elsevier.com/locate/ijfatigue Cold expansion effect on the initiation and the propagation of the fatigue crack A. Amrouche * , G. Mesmacque, S. Garcia, A. Talha UMR CNRS 8107, IUT A GMP, Le Recueil, Laboratoire de Me ´canique de Lille, Rue de la Recherche, BP 179, Villeneuve d’Ascq 59653, France Abstract In this study, an experimental and numerical investigation was carried out to quantify the effect of the cold expansion on the initiation and the propagation of the fatigue crack. The fatigue life improvement of the damaged structures after the cold expansion process was investigated with the single edge pre-cracked specimens of aluminium alloy which are used in land transport components. Three radii and three degrees of cold expansion were performed at the crack tip. The number of cycles to obtain a new crack initiation (life time), are analysed from the different cases. A numerical investigation with a numerical code (FEM ANSYS code) is conducted to determine the residual stress ﬁeld and the size of the plastic zone generated by the cold expansion and to establish the inﬂuence of the degree of cold expansion (DCE) on the different parameters. Three radii and six degrees of cold expansion were performed in this numerical investigation. It has been shown that the DCE has an inﬂuence on the size of the zone of compressive residual stresses (ZCRS) and on the size of the zone of plastic deformation (ZPD), but it appears that the DCE has no inﬂuence on the level of the maximum residual stresses in our case.  2003 Elsevier Ltd. All rights reserved. Keywords: Cold expansion; Life time; Crack initiation; Residual stresses 1. Introduction The fatigue crack can be stopped or delayed by a decrease in the notch sharpness and by residual com- pressive stresses at the crack tip. The usual technique to decrease the notch sharpness is the drilling at the crack tip and to induce residual compressive stresses is cold expansion [1–4]. The degree of cold expansion is deﬁned by the relation: DCE% = (D-d) d  100 where d is the hole drilling diameter and D diameter of rigid ball. Incidentally, crack propagation can be stopped for a * Corresponding author. Tel.: +33-3-20-67-73-28; fax: +33-3-20- 47-26-88. E-mail address: abdelwaheb.amrouche@univ-lille1.fr (A. Amrouche). 0142-1123/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0142-1123(03)00127-0 longer period, which is termed its ‘lifetime’. After a new crack initiation the crack propagation rate is lower than before drilling which contributes to safer working. In the present study, the hole drilling and cold expan- sion hole are investigated experimentally and numeri- cally. Three radii values and three degrees of cold expan- sion have been used. The hole radius, respectively, were r = 1.0, 2.5 and 3.0 mm. In this case, lifetime is con- trolled by the local radius and the local stress concen- tration factor [5]. Cold expansion was performed in order to achieve a ﬁnal radius of 3 mm. The initial radii were slightly smaller, so the cold expansion degrees vary from 0 to 4.3%. A numerical investigation is conducted to determine the residual stress ﬁeld and the plastic zone size gener- ated by the cold expansion and to analyse the inﬂuence of the degree of cold expansion (DCE) on the differ- ent parameters.