Analysis of crack propagation resistance of Al–Al2O3 particulate-reinforced composite friction stir.pdf

International Journal of Fatigue 31 (2009) 111–121Contents lists available at ScienceDirect International Journal of Fatigue journal homepage: www.elsevier .com/locate / i j fa t igueAnalysis of crack propagation resistance of Al–Al2O3 particulate-reinforced composite friction stir welded butt joints A. Pirondi *, L. Collini Department of Industrial Engineering, University of Parma, Viale G.P. Usberti 181/A, 43100 Parma, Italy a r t i c l e i n f o a b s t r a c tArticle history: Received 26 November 2007 Received in revised form 8 April 2008 Accepted 12 May 2008 Available online 17 May 2008 Keywords: Particulate metal–matrix composite Friction stir welding Fatigue crack growth Crack closure0142-1123/$ - see front matter  2008 Elsevier Ltd. A doi:10.1016/j.ijfatigue.2008.05.003 * Corresponding author. Tel.: +39 0521 905885; fax E-mail address: alessandro.pirondi@unipr.it (A. PirThis work is devoted to the analysis of fatigue crack propagation resistance of particulate metal-matrix composites butt joints obtained by friction stir welding. Two different aluminum alloy matrices rein- forced with alumina particles were examined. Tests were conducted on both parent material and welded joint for comparison. Fatigue crack propagation was carried out both within the weld nugget and in the thermo-mechanically altered zone at the side of the weld. The comparison between parent material and joint showed that the welding process affects fracture toughness and fatigue crack growth rate differently depending on the material. The analysis of crack path roughness helped to understand those differences in the fatigue crack growth rate. Therefore, roughness-induced crack closure arguments have been intro- duced to discuss data obtained under different testing conditions (parent material/joint, R-ratio, crack location, crack growth regime). Both the classical Elber’s approach and more recent approaches based on partial crack closure concept (adjusted compliance ratio, ACR, and 2/p me